Pseudomonas 3β‐hydroxysteroid dehydrogenase

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Abstract
The 3β‐hydroxysteroid dehydrogenase of Pseudomonas testosteroni commercially available was purified by an FPLC step and submitted to sequence determination by peptide analysis. The structure obtained reveals a 253‐residue polypeptide chain, with an N‐terminal, free α‐amino group, and a low cysteine content. Comparisons with other hydroxysteroid dehydrogenases recently characterized reveal distant similarities with prokaryotic and, to some extent, also eukaryotic forms of separate specificities. Residue identities with a Streptomyces 20β‐hydroxysteroid dehydrogenase are 35% and distributed over the entire molecule, whereas residue identities with the mammalian 17β‐hydroxysteroid dehydrogenase only constitute 20%, and are essentially limited to the N‐terminal and central parts, Nevertheless, all these enzymes exhibit a conserved tyrosine residue (position 151 in the present enzyme) noted as possibly having a functional role in some members of this protein family. Combined, the results establish the prokaryotic 3β‐hydroxysteroid dehydrogenase as belonging to the family of short‐chain alcohol dehydrogenases, reveal that the hydroxysteroid dehydrogenases are no more closely related than dehydrogenases with other enzyme activities within the family (e.g. glucose, ribitol, hydroxyprostaglandin dehydrogenases), show several of the mammalian hydroxysteroid dehydrogenases to have subunits of longer size with different patterns of similarity than those of the prokaryotic family members characterized, and define important segments of the coenzyme‐binding region for this enzyme group.

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