Two minor NAD+-specific aldehyde dehydrogenase fractions have been isolated from a Pseudomonas species grown on putrescine as the sole source of C and N. The chromatographic, enzymic, and electrophoretic behavior of these two fractions indicate that they are hybrids at the subunit level of two trimeric enzymes (succinic semialdehyde dehydrogenase and 4-aminobutanal dehydrogenase) previously purified from this organism. The molecular weights of these two fractions agree with the theoretical values for the hybrids. Immunodiffusion and inhibition of activity experiments conducted with antibodies to the two purified enzymes show antigenic similarities between either of the purified enzymes and the hybrids, but not between the purified enzymes themselves. Finally, electrophoresis in the presence of sodium dodecyl sulfate of the immunoprecipitate of one of the hybrids reveals the presence of subunits of both of the pure dehydrogenases. These results represent an unusual situation with no known precedent and indicate an evolutionary relationship between these enzymes.
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