Magni G, Drewniak M, Santarelli I, Huang C Y
Biochem Int. 1986 Apr;12(4):557-65.
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.
有人提出，酵母蛋白酶B在pH 5时的激活是由于蛋白酶A对该酶的一种特异性抑制剂IB的降解。然而，我们发现，当在pH 5的激活混合物中加入完全抑制蛋白酶A的胃蛋白酶抑制剂时，仍观察到蛋白酶B出现同样的时间依赖性激活。此外，不含蛋白酶A活性的蛋白酶B制剂在pH 5下孵育时仍会被激活。我们发现，蛋白酶B在pH 5时的激活主要是由于IB抑制作用的不可逆丧失，IB通过等电聚焦可分离为四条不同的带，其等电点分别为4.6、6.1、6.8和7.6。这四种形式的IB在pH 5时表现出不同程度的稳定性，这可能解释了过去报道的一些不同观察结果。
