Properties of Purine Nucleoside Phosphorylases from Spores and Vegetative Cells of Bacillus cereus and Their Modification by Orthophosphate

The purine nucleoside phosphorylases (PN-phosphorylase) from spores and vegetative cells of Bacillus cereus were each purified to electrophoretic homogeneity.The turnover numbers for the spore and vegetative cell enzymes were 145 and 181 moles of inosine cleaved per mole of enzyme per set, respectively.The PN-phosphorylase from vegetative cells was more anionic than that from the spores during gel electrophoresis in low concentrations of phosphate buffer.The Stokes' radii and sedimentation constants of the vegetative cell enzyme were constant over a wide range of phosphate concentrations.However, these parameters of the spore enzyme were concentration-dependent with respect to phosphate ion.The spore and vegetative cell enzymes were identical in mobility in acrylamide gel electrophoresis and heat resistance only at phosphate concentrations above the Michaelis constants for orthophosphate (7.3 X 10e3 M and 5.1 x 10Va M, respectively).The molecular weight of the spore enzyme increased from 87,000 to 123,000 while that of the vegetative cell enzyme remained at 107,000 over the phosphate concentration range 0 to 0.05 M. The half-life of spore PN-phosphorylase at 60" was 25 min in the absence of phosphate, but decreased to 5 min in 0.05 M phosphate, the value characteristic of the vegetative cell PN-phosphorylase.Purine nucleoside phosphorylase of Bacillus cereus is repressed in exponentially growing vegetative cells but appears with the onset of sporulation.Gardner and Kornberg (1) have shown that the synthesis of vegetative cell and spore forms is under the control of a single cistron.Although the enzymes should be identical, they have reported slight differences be-