Succinic Semialdehyde Dehydrogenase from a Pseudomonas Species

A molecular weight of 164,000 was determined for an NAD-specific succinic semialdehyde dehydrogenase from a Pseudomonas species by gel filtration, polyacrylamide electrophoresis with reference proteins, and ultracentrifugation. Electrophoresis in sodium dodecyl sulfate gave rise to a single subunit band with a molecular weight of 54,500, indicating that this enzyme is a three-subunit enzyme. Ultracentrifugal studies show that the enzyme dissociates into subunits at pH values of 9.7 or higher. Under conditions of low ionic strength and absence of sulfhydryl protective reagents, the enzyme reversibly associates to form a dimer with a molecular weight of about 320,000 as calculated from the Svedberg equation and from polyacrylamide electrophoresis with reference proteins. Immunodiffusion in the absence of NaCl gave one precipitin line corresponding to the monomer, while immunodiffusion in the presence of 0.15 m NaCl gave three precipitin lines which can be correlated to the subunit, the monomer, and the dimer. Antisuccinic semialdehyde dehydrogenase cross-reacts with other enzyme fractions from this Pseudomonas which are active toward 3-aminopropanal and 4-aminobutanal as well as succinic semialdehyde. It is suggested that these fractions represent hybrids of succinic semialdehyde dehydrogenase and aminoaldehyde dehydrogenases.