Aminopeptidase from Sphingomonas capsulata

A novel aminopeptidase with unique substrate specificity was purified from a culture broth of Sphingomonas capsulata, This is the first reported amino peptidase to demonstrate broad substrate specificity and yet release glycin e and alanine with the highest efficacy. On a series of pentapeptide amides with different N-terminal amino acids, this enzyme efficiently releases gl ycine, alanine, leucine, proline, and glutamate with the lowest turnover va lue of 370 min(-1) for glutamate, At pH 7.5 (pH optimum) and 25 degreesC, t he kinetic parameters for alanine para-nitroanilide were found to be k(cat) = 7600 min(-1) and K-m = 14 mM. For alanine beta -naphthylamide, they were k(cat) = 860 min(-1) and K-m = 6.7 mm, Polymerase chain reaction primers w ere designed based upon obtained internal sequences of the wild type enzyme . The subsequent product was then used to acquire the full-length gene from an S, capsulata genomic library. An open reading frame encoding a protein of 670 amino acids was obtained. The translated protein has a putative sign al peptide that directs the enzyme into the supernatant, A search of the am ino acid sequence revealed no significant homology to any known aminopeptid ases in the available data bases.