Purification and some properties of two extracellular proteolytic enzymes produced by Vibrio SA1

The purification and characterisation of an extracellular endo and amino-peptidase of the marine Vibrio SA1 is described. The endopeptidase was purified by ammonium sulphate precipitation, gel filtration and affinity chromatography. It had a molecular weight of approximately 31,000, a pH optimum at 7.8 and a temperature optimum at 50 C. The enzyme was rapidly inactivated at 65 C. The aminopeptidase was purified by ammonium sulphate precipitation, gel filtration and preparative polyacrylamide gel electrophoresis. This enzyme had a molecular weight of approximately 21,000, a pH optimum at 8.6 and a temperature optimum at 60 C. Both proteases were inactivated by EDTA while reactivation occurred by Ca2+, Zn2+ and Mg2+ ions. The endopeptidase hydrolysed several peptide bonds in the oxidized B-chain of insulin, particularly those involving amino groups of hydrophobic amino acid residues with bulky side chains. It was unable to hydrolyse synthetic dipeptides, but a number of tripeptides were hydrolysed at a low rate. The aminopeptidase hydrolysed leucinamide and di- and tripeptides containing hydrophobic bulky amino acids as the N-terminal residue. It was concluded that the endopeptidase and the aminopeptidase of Vibrio SA1 possess complementary specificities.