title: Reexamination of the activation of yeast proteinase B at pH 5: loss of inhibition effect of proteinase B inhibitors.
abstract: The activation of yeast proteinase B at pH 5 has been suggested to be due to the degradation of a specific inhibitor for the enzyme, IB, by proteinase A. However, we found that when pepstatin, which completely inhibits proteinase A, was included in the pH 5 activation mixture, the same time-dependent activation of proteinase B was observed. Furthermore, proteinase B preparations that were void of proteinase A activity were still activated by incubation at pH 5. We found that the activation of proteinase B at pH 5 was due primarily to the irreversible loss of inhibitory effect of IB, which can be resolved by isoelectrofocusing into four distinct bands with isoelectric points of 4.6, 6.1, 6.8 and 7.6. These four forms of IB showed varying degrees of stability at pH 5, which may explain some of the differing observations reported in the past.
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D011480:Protease Inhibitors; D012697:Serine Endopeptidases; D013997:Time Factors; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D010450:Endopeptidases; D011480:Protease Inhibitors; D012697:Serine Endopeptidases; C023302:yeast proteinase B; D029701:Saccharomyces cerevisiae Proteins