Characterization of the Saccharomyces cerevisiaeCytosine Transporter Using Energizable Plasma Membrane Vesicles

The purine-cytosine permease is a carrier localized in the plasma membrane of the yeast Saccharomyces cerevisiae. The energetics of cytosine transport catalyzed by this permease has been studied in an artificial system obtained by fusion between proteoliposomes containing beef heart cytochromec oxidase and plasma membrane-enriched fractions of aS. cerevisiae strain overexpressing the permease. Upon addition of an energy donor, a proton-motive force (inside alkaline and negative) is created in this system and promotes cytosine accumulation. By using different phospholipids, it is shown that cytosine uptake is dependent on the phospholipids surrounding the carrier. It was demonstrated that the purine-cytosine permease is able to catalyze a secondary active transport of cytosine. By using nigericin and valinomycin, the ΔpH component of the proton-motive force is shown to be the only force driving nucleobase accumulation. Moreover, transport measurements done at two pH values have shown that alkalinization of intravesicular pH leads to a significant increase in cytosine uptake rate. Finally, no specific role of K+ ions on cytosine transport could be demonstrated in this system. The purine-cytosine permease is a carrier localized in the plasma membrane of the yeast Saccharomyces cerevisiae. The energetics of cytosine transport catalyzed by this permease has been studied in an artificial system obtained by fusion between proteoliposomes containing beef heart cytochromec oxidase and plasma membrane-enriched fractions of aS. cerevisiae strain overexpressing the permease. Upon addition of an energy donor, a proton-motive force (inside alkaline and negative) is created in this system and promotes cytosine accumulation. By using different phospholipids, it is shown that cytosine uptake is dependent on the phospholipids surrounding the carrier. It was demonstrated that the purine-cytosine permease is able to catalyze a secondary active transport of cytosine. By using nigericin and valinomycin, the ΔpH component of the proton-motive force is shown to be the only force driving nucleobase accumulation. Moreover, transport measurements done at two pH values have shown that alkalinization of intravesicular pH leads to a significant increase in cytosine uptake rate. Finally, no specific role of K+ ions on cytosine transport could be demonstrated in this system. Living cells have to take up various ions and metabolites from extracellular medium. Recent reviews have listed many hydrophobic proteins of the yeast Saccharomyces cerevisiae plasma membrane involved in specific transport of a large array of molecules, such as hexoses and amino acids, as well as potassium and sulfate ions (1Van der Rest M.E. Kamminga A.H. Nakano A. Anraku Y. Poolman B. Konings W.N. Microbiol. Rev. 1995; 59: 304-322Crossref PubMed Google Scholar, 2André B. Yeast. 1995; 11: 1575-1611Crossref PubMed Scopus (207) Google Scholar). Many of these proteins have been reported to work as secondary active carriers. Most of them are symports coupling the utilization of the proton gradient, built up by the H+-ATPase of the plasma membrane, to the uptake of different kinds of molecules (1Van der Rest M.E. Kamminga A.H. Nakano A. Anraku Y. Poolman B. Konings W.N. Microbiol. Rev. 1995; 59: 304-322Crossref PubMed Google Scholar).Purine-cytosine permease from S. cerevisiae is one of these plasma membrane carriers (3Weber E. Rodriguez C. Chevallier M.R. Jund R. Mol. Microbiol. 1990; 4: 585-596Crossref PubMed Scopus (63) Google Scholar, 4Schmidt R. Manolson M.F. Chevallier M.R. Proc. Natl. Acad. Sci. U. S. A. 1984; 81: 6276-6280Crossref PubMed Scopus (25) Google Scholar). In vivo, this permease seems to mediate the co-transport of proton and purine bases (adenine, hypoxanthine, and guanine) or a pyrimidine base (cytosine) (5Polak A. Grenson M. Eur. J. Biochem. 1973; 32: 276-282Crossref PubMed Scopus (75) Google Scholar, 6Chevallier M.R. Jund R. Lacroute F. J. Bacteriol. 1975; 122: 629-641Crossref PubMed Google Scholar), the energy source of this active transport being the proton electrochemical gradient built up by the H+-ATPase (7Goffeau A. Slayman C.W. Biochim. Biophys. Acta. 1981; 639: 197-223Crossref PubMed Scopus (334) Google Scholar, 8Serrano R. Biochim. Biophys. Acta. 1988; 947: 1-28Crossref PubMed Scopus (337) Google Scholar). By measuring simultaneously hypoxanthine uptake and H+and K+ fluxes, it has been proposed that purine translocation through the S. cerevisiae plasma membrane is an electroneutral base/H+ symport with a K+antiport (9Reichert U. Forêt M. FEBS Lett. 1977; 83: 325-328Crossref PubMed Scopus (28) Google Scholar). In contrast to this, it has been proposed in other experiments carried out on a S. cerevisiae strain (lacking cytosine deaminase and overexpressing the purine-cytosine permease) in ATP-depletion conditions, that the pump works as an electrogenic proton symport (10Hopkins P. Chevallier M.R. Jund R. Eddy A.A. FEMS Microbiol. Lett. 1988; 49: 173-177Crossref Scopus (31) Google Scholar) with a H+/base stoichiometry close to 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar).In addition, studies have been carried on S. cerevisiaepurine-cytosine permease proficient strains carrying plasmid-encoded multiple copies of either wild type or mutated FCY2 gene, encoding the purine-cytosine permease. We have analyzed the effects of pH on in vivo uptake and in vitro equilibrium binding of nucleobases, and have shown a key role played by a protonable group of the permease the binding of the translocation C. E. Chevallier J. Eur. J. Biochem. 1992; PubMed Scopus Google studies of uptake in cells be analyzed in close the the the be the of the the of the be no specific of the of on transport be it is to the transport in a well with an in vitro system obtained by membrane fusion between plasma membrane fractions and proteoliposomes containing a a system that a proton-motive force has been the of various transport in Konings W.N. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar) and of carriers of yeast plasma membrane a der Rest M.E. Kamminga A.H. Nakano A. Anraku Y. Poolman B. Konings W.N. Microbiol. Rev. 1995; 59: 304-322Crossref PubMed Google Scholar).In this have this to the energetics of the transport catalyzed by the purine-cytosine permease of the plasma membrane of S. cerevisiae. uptake has been analyzed in artificial obtained by fusion between proteoliposomes containing beef heart oxidase and plasma membrane-enriched fractions of a S. cerevisiae strain overexpressing the permease. of the transport to in have been with these this it is demonstrated that the purine-cytosine permease is a secondary active transport only by the ΔpH component of the proton-motive In addition, it is shown that the of uptake the pH is and that the carrier is able to cytosine at the of accumulation. The of the on the uptake is this cytosine transport was analyzed in artificial obtained by fusion of plasma membrane-enriched fractions of S. cerevisiae containing the purine-cytosine permease and proteoliposomes containing an to that obtained by other E. J. J. PubMed Google Scholar, M. Eur. J. Biochem. PubMed Scopus Google Scholar, F. C. Yeast. PubMed Scopus Google Scholar). The cytochromec oxidase in specific by and addition to that with beef heart C. L. J. 1975; PubMed Google Scholar). of that The equilibrium binding values and cytosine the as with plasma membrane-enriched of a in oxidase at pH values the experiments done at pH or pH conditions, the purine-cytosine permease nucleobase uptake on cells and equilibrium binding on plasma membrane fractions at these pH C. E. Chevallier J. Eur. J. Biochem. 1992; PubMed Scopus Google energy containing purine-cytosine permease able to transport in a and The of cytosine uptake was different to that of and The uptake from values in this was a that cells is close to C. F. Chevallier J. Eur. J. Biochem. 1990; PubMed Scopus Google Scholar). of a carrier is in and to effects of and plasma membrane and and to the of the of the carrier in the artificial in that cytosine uptake is a secondary active transport on the of a proton-motive force at one of The cytosine was only the was have been done to this by the of of the other carriers E. J. J. PubMed Google Scholar, M. Eur. J. Biochem. PubMed Scopus Google Scholar). In addition, in the fusion the the of the and the of through the The obtained from these the or of the of the carrier have been by with phospholipids from various from E. was the other phospholipids, and the phospholipids from plasma membrane fractions of S. cerevisiae. has been secondary active carriers E. J. J. PubMed Google Scholar, Konings W.N. 1988; PubMed Scopus Google Scholar). Moreover, from E. was shown to the carrier the well amino permease of in vivo in a membrane this Konings W.N. 1988; PubMed Scopus Google Scholar). work is to yeast phospholipids uptake and of cytosine in of either the ΔpH or the component of the that the cytosine active transport was by the ΔpH component and that the with the ΔpH In the the shown in in the of valinomycin, the a of a by a was to the energy source by the of a of the to the of a stoichiometry of 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar) and the system was to one ΔpH to a of In the various uptake experiments values from to of that could these in the fusion was a large of oxidase proteoliposomes as with the plasma membrane in the the purine-cytosine permease. it was to the of as done containing other the from to of E. J. J. PubMed Google Scholar, F. C. Yeast. PubMed Scopus Google Scholar, R. J. Bacteriol. PubMed Google Scholar). of the of the carrier in the nucleobases, and of the specific of the a to be to the uptake In such conditions, as it the to values the large such a hydrophobic is shown by uptake done at cytosine of and to of and has been and other carriers Konings W.N. J. PubMed Google Scholar). this it to the with the stoichiometry of 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar). Moreover, of K+ by ions in the uptake the of the transport this is with the of (10Hopkins P. Chevallier M.R. Jund R. Eddy A.A. FEMS Microbiol. Lett. 1988; 49: 173-177Crossref Scopus (31) Google Scholar). the nucleobase transport is K+ or the permease through system in the plasma an to this be that the cytosine transport is electroneutral by that the carrier take of the cytosine at the pH the a of cytosine is with a this be in with the that the cytosine only on the ΔpH component of the proton-motive the other was the role played by the pH on the uptake alkaline values to of the of cytosine uptake In this it is to be that was a of the of cytosine uptake on the is to be this by be in the active translocation alkalinization of the leads to an increase in the of of the permease. a this increase the of the carrier involved in the of the as the of cytosine transport (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar) and of transport S. Konings W.N. J. Bacteriol. PubMed Scopus Google Scholar). It be to a only on these are with the cells cytosine the cytosine was close to and the was C. F. Chevallier J. Eur. J. Biochem. 1990; PubMed Scopus Google Scholar). these conditions, was a ΔpH close to pH the was pH pH C. and pH values are the in vivo cytosine active to equilibrium between ΔpH and the cytosine a stoichiometry of in vivo ΔpH could be in experiments at the of have shown that no by cytosine and that the of was the of and has been in other transport system Biochem. J. PubMed Scopus Google Scholar). In it has been shown that yeast and are M. Eur. J. Biochem. PubMed Scopus Google Scholar, Biochem. J. PubMed Scopus Google Scholar). is the permease By using plasma membrane it was shown that the transport was E. A. J. PubMed Google Scholar). by using a the group it to be and by J. PubMed Scopus Google Scholar). in from plasma membrane is the of cytosine and the to that be obtained by the system in this work is a in the of the purine-cytosine permease. It has to the the carrier a transport the ΔpH component of the is the driving force the pH a role in the uptake and the purine-cytosine permease K+ the of the system of the translocation and that of the transport a system. Living cells have to take up various ions and metabolites from extracellular medium. Recent reviews have listed many hydrophobic proteins of the yeast Saccharomyces cerevisiae plasma membrane involved in specific transport of a large array of molecules, such as hexoses and amino acids, as well as potassium and sulfate ions (1Van der Rest M.E. Kamminga A.H. Nakano A. Anraku Y. Poolman B. Konings W.N. Microbiol. Rev. 1995; 59: 304-322Crossref PubMed Google Scholar, 2André B. Yeast. 1995; 11: 1575-1611Crossref PubMed Scopus (207) Google Scholar). Many of these proteins have been reported to work as secondary active carriers. Most of them are symports coupling the utilization of the proton gradient, built up by the H+-ATPase of the plasma membrane, to the uptake of different kinds of molecules (1Van der Rest M.E. Kamminga A.H. Nakano A. Anraku Y. Poolman B. Konings W.N. Microbiol. Rev. 1995; 59: 304-322Crossref PubMed Google Scholar). permease from S. cerevisiae is one of these plasma membrane carriers (3Weber E. Rodriguez C. Chevallier M.R. Jund R. Mol. Microbiol. 1990; 4: 585-596Crossref PubMed Scopus (63) Google Scholar, 4Schmidt R. Manolson M.F. Chevallier M.R. Proc. Natl. Acad. Sci. U. S. A. 1984; 81: 6276-6280Crossref PubMed Scopus (25) Google Scholar). In vivo, this permease seems to mediate the co-transport of proton and purine bases (adenine, hypoxanthine, and guanine) or a pyrimidine base (cytosine) (5Polak A. Grenson M. Eur. J. Biochem. 1973; 32: 276-282Crossref PubMed Scopus (75) Google Scholar, 6Chevallier M.R. Jund R. Lacroute F. J. Bacteriol. 1975; 122: 629-641Crossref PubMed Google Scholar), the energy source of this active transport being the proton electrochemical gradient built up by the H+-ATPase (7Goffeau A. Slayman C.W. Biochim. Biophys. Acta. 1981; 639: 197-223Crossref PubMed Scopus (334) Google Scholar, 8Serrano R. Biochim. Biophys. Acta. 1988; 947: 1-28Crossref PubMed Scopus (337) Google Scholar). By measuring simultaneously hypoxanthine uptake and H+and K+ fluxes, it has been proposed that purine translocation through the S. cerevisiae plasma membrane is an electroneutral base/H+ symport with a K+antiport (9Reichert U. Forêt M. FEBS Lett. 1977; 83: 325-328Crossref PubMed Scopus (28) Google Scholar). In contrast to this, it has been proposed in other experiments carried out on a S. cerevisiae strain (lacking cytosine deaminase and overexpressing the purine-cytosine permease) in ATP-depletion conditions, that the pump works as an electrogenic proton symport (10Hopkins P. Chevallier M.R. Jund R. Eddy A.A. FEMS Microbiol. Lett. 1988; 49: 173-177Crossref Scopus (31) Google Scholar) with a H+/base stoichiometry close to 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar). In addition, studies have been carried on S. cerevisiaepurine-cytosine permease proficient strains carrying plasmid-encoded multiple copies of either wild type or mutated FCY2 gene, encoding the purine-cytosine permease. We have analyzed the effects of pH on in vivo uptake and in vitro equilibrium binding of nucleobases, and have shown a key role played by a protonable group of the permease the binding of the translocation C. E. Chevallier J. Eur. J. Biochem. 1992; PubMed Scopus Google Scholar). studies of uptake in cells be analyzed in close the the the be the of the the of the be no specific of the of on transport be it is to the transport in a well with an in vitro system obtained by membrane fusion between plasma membrane fractions and proteoliposomes containing a a system that a proton-motive force has been the of various transport in Konings W.N. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar) and of carriers of yeast plasma membrane a der Rest M.E. Kamminga A.H. Nakano A. Anraku Y. Poolman B. Konings W.N. Microbiol. Rev. 1995; 59: 304-322Crossref PubMed Google Scholar). In this have this to the energetics of the transport catalyzed by the purine-cytosine permease of the plasma membrane of S. cerevisiae. uptake has been analyzed in artificial obtained by fusion between proteoliposomes containing beef heart oxidase and plasma membrane-enriched fractions of a S. cerevisiae strain overexpressing the permease. of the transport to in have been with these this it is demonstrated that the purine-cytosine permease is a secondary active transport only by the ΔpH component of the proton-motive In addition, it is shown that the of uptake the pH is and that the carrier is able to cytosine at the of accumulation. The of the on the uptake is this cytosine transport was analyzed in artificial obtained by fusion of plasma membrane-enriched fractions of S. cerevisiae containing the purine-cytosine permease and proteoliposomes containing an to that obtained by other E. J. J. PubMed Google Scholar, M. Eur. J. Biochem. PubMed Scopus Google Scholar, F. C. Yeast. PubMed Scopus Google Scholar). The cytochromec oxidase in specific by and addition to that with beef heart C. L. J. 1975; PubMed Google Scholar). of that The equilibrium binding values and cytosine the as with plasma membrane-enriched of a in oxidase at pH values the experiments done at pH or pH conditions, the purine-cytosine permease nucleobase uptake on cells and equilibrium binding on plasma membrane fractions at these pH C. E. Chevallier J. Eur. J. Biochem. 1992; PubMed Scopus Google energy containing purine-cytosine permease able to transport in a and The of cytosine uptake was different to that of and The uptake from values in this was a that cells is close to C. F. Chevallier J. Eur. J. Biochem. 1990; PubMed Scopus Google Scholar). of a carrier is in and to effects of and plasma membrane and and to the of the of the carrier in the artificial in that cytosine uptake is a secondary active transport on the of a proton-motive force at one of The cytosine was only the was have been done to this by the of of the other carriers E. J. J. PubMed Google Scholar, M. Eur. J. Biochem. PubMed Scopus Google Scholar). In addition, in the fusion the the of the and the of through the The obtained from these the or of the of the carrier have been by with phospholipids from various from E. was the other phospholipids, and the phospholipids from plasma membrane fractions of S. cerevisiae. has been secondary active carriers E. J. J. PubMed Google Scholar, Konings W.N. 1988; PubMed Scopus Google Scholar). Moreover, from E. was shown to the carrier the well amino permease of in vivo in a membrane this Konings W.N. 1988; PubMed Scopus Google Scholar). work is to yeast phospholipids uptake and of cytosine in of either the ΔpH or the component of the that the cytosine active transport was by the ΔpH component and that the with the ΔpH In the the shown in in the of valinomycin, the a of a by a was to the energy source by the of a of the to the of a stoichiometry of 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar) and the system was to one ΔpH to a of In the various uptake experiments values from to of that could these in the fusion was a large of oxidase proteoliposomes as with the plasma membrane in the the purine-cytosine permease. it was to the of as done containing other the from to of E. J. J. PubMed Google Scholar, F. C. Yeast. PubMed Scopus Google Scholar, R. J. Bacteriol. PubMed Google Scholar). of the of the carrier in the nucleobases, and of the specific of the a to be to the uptake In such conditions, as it the to values the large such a hydrophobic is shown by uptake done at cytosine of and to of and has been and other carriers Konings W.N. J. PubMed Google Scholar). this it to the with the stoichiometry of 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar). Moreover, of K+ by ions in the uptake the of the transport this is with the of (10Hopkins P. Chevallier M.R. Jund R. Eddy A.A. FEMS Microbiol. Lett. 1988; 49: 173-177Crossref Scopus (31) Google Scholar). the nucleobase transport is K+ or the permease through system in the plasma an to this be that the cytosine transport is electroneutral by that the carrier take of the cytosine at the pH the a of cytosine is with a this be in with the that the cytosine only on the ΔpH component of the proton-motive the other was the role played by the pH on the uptake alkaline values to of the of cytosine uptake In this it is to be that was a of the of cytosine uptake on the is to be this by be in the active translocation alkalinization of the leads to an increase in the of of the permease. a this increase the of the carrier involved in the of the as the of cytosine transport (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar) and of transport S. Konings W.N. J. Bacteriol. PubMed Scopus Google Scholar). It be to a only on these are with the cells cytosine the cytosine was close to and the was C. F. Chevallier J. Eur. J. Biochem. 1990; PubMed Scopus Google Scholar). these conditions, was a ΔpH close to pH the was pH pH C. and pH values are the in vivo cytosine active to equilibrium between ΔpH and the cytosine a stoichiometry of in vivo ΔpH could be in experiments at the of have shown that no by cytosine and that the of was the of and has been in other transport system Biochem. J. PubMed Scopus Google Scholar). In it has been shown that yeast and are M. Eur. J. Biochem. PubMed Scopus Google Scholar, Biochem. J. PubMed Scopus Google Scholar). is the permease By using plasma membrane it was shown that the transport was E. A. J. PubMed Google Scholar). by using a the group it to be and by J. PubMed Scopus Google Scholar). in from plasma membrane is the of cytosine and the to that be obtained by the system in this work is a in the of the purine-cytosine permease. It has to the the carrier a transport the ΔpH component of the is the driving force the pH a role in the uptake and the purine-cytosine permease K+ the of the system of the translocation and that of the transport a system. In this cytosine transport was analyzed in artificial obtained by fusion of plasma membrane-enriched fractions of S. cerevisiae containing the purine-cytosine permease and proteoliposomes containing an to that obtained by other E. J. J. PubMed Google Scholar, M. Eur. J. Biochem. PubMed Scopus Google Scholar, F. C. Yeast. PubMed Scopus Google Scholar). The cytochromec oxidase in specific by and addition to that with beef heart C. L. J. 1975; PubMed Google Scholar). of that The equilibrium binding values and cytosine the as with plasma membrane-enriched of a in oxidase at pH values the experiments done at pH or pH conditions, the purine-cytosine permease nucleobase uptake on cells and equilibrium binding on plasma membrane fractions at these pH C. E. Chevallier J. Eur. J. Biochem. 1992; PubMed Scopus Google Scholar). Upon energy containing purine-cytosine permease able to transport in a and The of cytosine uptake was different to that of and The uptake from values in this was a that cells is close to C. F. Chevallier J. Eur. J. Biochem. 1990; PubMed Scopus Google Scholar). of a carrier is in and to effects of and plasma membrane and and to the of the of the carrier in the artificial system. in that cytosine uptake is a secondary active transport on the of a proton-motive force at one of The cytosine was only the was have been done to this by the of of the other carriers E. J. J. PubMed Google Scholar, M. Eur. J. Biochem. PubMed Scopus Google Scholar). In addition, in the fusion the the of the and the of through the The obtained from these the or of the of the carrier have been by with phospholipids from various from E. was the other phospholipids, and the phospholipids from plasma membrane fractions of S. cerevisiae. has been secondary active carriers E. J. J. PubMed Google Scholar, Konings W.N. 1988; PubMed Scopus Google Scholar). Moreover, from E. was shown to the carrier the well amino permease of in vivo in a membrane this Konings W.N. 1988; PubMed Scopus Google Scholar). work is to yeast phospholipids uptake and of cytosine in of either the ΔpH or the component of the that the cytosine active transport was by the ΔpH component and that the with the ΔpH In the the shown in in the of valinomycin, the a of a by a was to the energy source by the of a of the to the of a stoichiometry of 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar) and the system was to one ΔpH to a of In the various uptake experiments values from to of that could these in the fusion was a large of oxidase proteoliposomes as with the plasma membrane in the the purine-cytosine permease. it was to the of as done containing other the from to of E. J. J. PubMed Google Scholar, F. C. Yeast. PubMed Scopus Google Scholar, R. J. Bacteriol. PubMed Google Scholar). of the of the carrier in the nucleobases, and of the specific of the a to be to the uptake In such conditions, as it the to values the large such a hydrophobic is shown by uptake done at cytosine of and to of and has been and other carriers Konings W.N. J. PubMed Google Scholar). this it to the with the stoichiometry of 1 (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar). Moreover, of K+ by ions in the uptake the of the transport this is with the of (10Hopkins P. Chevallier M.R. Jund R. Eddy A.A. FEMS Microbiol. Lett. 1988; 49: 173-177Crossref Scopus (31) Google Scholar). the nucleobase transport is K+ or the permease through system in the plasma an to this be that the cytosine transport is electroneutral by that the carrier take of the cytosine at the pH the a of cytosine is with a this be in with the that the cytosine only on the ΔpH component of the proton-motive the other was the role played by the pH on the uptake alkaline values to of the of cytosine uptake In this it is to be that was a of the of cytosine uptake on the is to be this by be in the active translocation alkalinization of the leads to an increase in the of of the permease. a this increase the of the carrier involved in the of the as the of cytosine transport (11Hopkins P. Shaw R. Acik L. Oliver S. Eddy A.A. Yeast. 1992; 8: 1053-1064Crossref PubMed Scopus (8) Google Scholar) and of transport S. Konings W.N. J. Bacteriol. PubMed Scopus Google Scholar). It be to a only on these are with the In cells cytosine the cytosine was close to and the was C. F. Chevallier J. Eur. J. Biochem. 1990; PubMed Scopus Google Scholar). these conditions, was a ΔpH close to pH the was pH pH C. and pH values are the in vivo cytosine active to equilibrium between ΔpH and the cytosine a stoichiometry of in vivo ΔpH could be in Finally, experiments at the of have shown that no by cytosine and that the of was the of and has been in other transport system Biochem. J. PubMed Scopus Google Scholar). In it has been shown that yeast and are M. Eur. J. Biochem. PubMed Scopus Google Scholar, Biochem. J. PubMed Scopus Google Scholar). is the permease By using plasma membrane it was shown that the transport was E. A. J. PubMed Google Scholar). by using a the group it to be and by J. PubMed Scopus Google Scholar). in from plasma membrane is the of cytosine and the to that be obtained by In the system in this work is a in the of the purine-cytosine permease. It has to the the carrier a transport the ΔpH component of the is the driving force the pH a role in the uptake and the purine-cytosine permease K+ the of the system of the translocation and that of the transport a system. We on the and R. the