Purification and characterisation of a serine peptidase from the marine psychrophile strain PA-43

An extracellular serine peptidase, purified from the culture supernatant of the sub-Arctic psychrophilic bacterium strain PA-43, is monomeric, with a relative molecular mass of 76 000, and an unusually low pI of 3.8. The pept idase is active towards N-succinyl AAPF p-nitroanilide and N-succinyl AAPL p-nitroanilide, indicating a chymotrypsin-like substrate specificity. It is inhibited by the serine peptidase inactivator phenylmethylsulfonyl fluorid e, but not by EDTA or EGTA, suggesting that added metal ions are not necess ary for activity. The enzyme is most active at pH 8.3 and at 55-60 degreesC , although it is unstable at 60 degreesC. It is nevertheless remarkably sta ble for an enzyme from a psychrophilic microorganism, remaining active afte r I week at 20 degreesC and after five freeze-thaw cycles. Comparison of th e N-terminal 40 amino acid residues with other archived sequences revealed highest similarity to the alkaline serine protease (aprx) from Bacillus sub tilis. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.