Waxman L, Krebs E G
J Biol Chem. 1978 Sep 10;253(17):5888-91.
Low salt extracts from homogenates of bovine cardiac muscle contain two protease inhibitors, one specific for the calcium-activated protease from this tissue and the other for trypsin and chymotrypsin, but no other serine proteases, including plasmin, thrombin, and subtilisin. The former, which can be separated from the protease by chromatography on DEAE-cellulose, is a protein with a molecular weight of 270,000. Its action is not based on the sequestering of calcium, and it is present in large excess over the amount of calcium-activated protease in this tissue. The trypsin inhibitor, which has a molecular weight of 70,000, is estimated to be present at approximately 300 microgram/g, wet weight, of tissue. The identification of inhibitors such as these in the cytoplasm may explain why nonlysosomal proteolytic activity has been thought to be insignificant in the overall turnover of intracellular protein and suggests that a re-evaluation of this possibility is necessary.
牛心肌匀浆的低盐提取物含有两种蛋白酶抑制剂，一种对该组织中的钙激活蛋白酶具有特异性，另一种对胰蛋白酶和糜蛋白酶具有特异性，但对包括纤溶酶、凝血酶和枯草杆菌蛋白酶在内的其他丝氨酸蛋白酶没有抑制作用。前者可通过在DEAE - 纤维素上进行色谱分离与蛋白酶分开，是一种分子量为270,000的蛋白质。其作用并非基于对钙的螯合，且在该组织中其含量大大超过钙激活蛋白酶的量。分子量为70,000的胰蛋白酶抑制剂估计在组织湿重中约为300微克/克。在细胞质中鉴定出这样的抑制剂可能解释了为什么非溶酶体蛋白水解活性在细胞内蛋白质的整体周转中被认为是微不足道的，并表明有必要重新评估这种可能性。
