α-Ketoglutaric Semialdehyde Dehydrogenase of Pseudomonas

In Pseudomonas putida, two induced catabolic pathways, from hydroxyproline and from d-glucarate, converge at a common step, dehydrogenation of α-ketoglutaric semialdehyde to α-ketoglutarate. The dehydrogenases respectively induced by hydroxyproline or glucarate were both purified to homogeneity and compared. In contrast to an earlier, more limited comparison, which revealed no reliable difference between them, detailed electrophoretic, structural, immunological, and genetic studies now show them to be distinct proteins, although closely similar in most kinetic properties studied, as well as in molecular weight, subunit status, and amino acid composition. An unexpected finding was the presence of enzymatic activity for the preceding step in the hydroxyproline pathway (Δ1-pyrroline-4-hydroxy-2-carboxylate deaminase) associated with both the glucarate-induced and hydroxyproline-induced dehydrogenases. In each enzyme, the finding of a 4- to 5-fold lower number of separable tryptic peptides compared with the number expected from subunit size and amino acid composition suggests possible sequence redundancy but needs further investigation.