CONCERNING THE NATURE OF THE α- AND β-LYTIC PROTEASES OF SORANGIUM SP.

Abstract

The α-lytic protease is readily inhibited by diisopropyl phosphorofluoridate (DFP) and the yield of serine phosphate from acid-hydrolyzed, DFP-inhibited enzyme indicates that DFP esterifies one serine residue of the enzyme. Acid digests of enzyme treated with isopropyl methylphosphonofluoridate-32P (sarin) show much the same electrophoretic patterns of 32P-labelled peptides as similar digests of sarin-treated trypsin and chymotrypsin; amino acid analyses and N-terminal amino acid analyses of peptides isolated from the digest confirm that the α-enzyme has the same sequence (Asp-Ser*-Gly-Gly) around the reactive serine residue as the pancreatic enzymes. At present, the α-enzyme is the only microbial "serine protease" which is known to have this sequence. It is also unique as a serine protease in that it has only one histidine residue.The β-lytic enzyme is not inhibited by DFP and shows no evidence of reactivity towards sarin. Its zinc atom can be removed by o-phenanthroline without loss of lytic activity. At present, it cannot be classed in any of the major groups of proteases.