title: The substrate specificity of proteinase B from baker's yeast.
abstract: The substrate specificity of proteinase B (EC 3.4.22.9) from Baker's yeast was studied. Experiments with unblocked synthetic peptides indicated that the enzyme has no aminopeptidase activity. The proteinase cleaves trypsin substrates like Bz-Arg-OEt, Bz-Arg-pNA and Bz-Ile-Glu-Gly-Arg-pNA and chymotrypsin substrates like Ac-Tyr-OEt and Bz-Tyr-pNA. The Km value for Ac-Tyr-OEt is similar to that of chymotrypsin A, but the catalytic activity per mol proteinase B amounts to only 1/20 that of chymotrypsin A. Km and kcat for Bz-Arg-OEt are 1/50 and 1/7 as high as the corresponding values determined for trypsin. Proteinase B cleaved the oxidized insulin B chain with an initial rapid cleavage step at Leu(15)-Tyr(16) and Phe(24)-Phe(25). Slower hydrolysis was observed at Gln(4)-His(5), Leu(11)-Val(12) Tyr(16)-Leu(17), Leu(17)-Val(18), Arg(22)-Gly(23) and Phe(25)-Tyr(26). These results suggest that the specificity of proteinase B is comparable to the specificity of porcine chymotrypsin C as well as of trypsin. When the hexapeptide Leu-Trp-Met-Arg-Phe-Ala was used as a substrate for proteinase B, the enzyme preferentially attacked at Arg-Phe and more slowly at Trp-Met.
mesh_terms: D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D007328:Insulin; D009842:Oligopeptides; D010446:Peptide Fragments; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D012697:Serine Endopeptidases; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D002918:Chymotrypsin; D010450:Endopeptidases; D007328:Insulin; D009842:Oligopeptides; D010446:Peptide Fragments; D012697:Serine Endopeptidases; D014357:Trypsin; C023302:yeast proteinase B; D029701:Saccharomyces cerevisiae Proteins