Bausserman L L, Herbert P N
Biochemistry. 1984 May 8;23(10):2241-5. doi: 10.1021/bi00305a023.
We have investigated the protease activity, present in human serum, that digests the serum amyloid A (SAA) protein. SAA radiolabeled with 125I was incubated at 37 degrees C with serum and plasma and analyzed for degradation products by alkaline urea-polyacrylamide gel electrophoresis and gel filtration chromatography. Serum initially digested SAA to intermediates of 3000-5000 in molecular weight, and these were further degraded to smaller peptides with prolonged incubation. SAA was not degraded by plasma anticoagulated with ethylenediaminetetraacetic acid (EDTA) or heparin. Recalcification of plasma anticoagulated with EDTA led to the generation of protease activity against SAA whereas EDTA plasma defibrinated with thrombin was inactive. We employed both nonselective and selective protease inhibitors and synthetic substrates for kallikrein and plasmin to further characterize the serum protease. These studies demonstrated that degradation of SAA is not directly attributable to enzymes involved in coagulation, kinin formation, or fibrinolysis, but the unidentified protease may be activated by one of the clotting factors. The specificity of the SAA degradation was demonstrated in experiments with three of the well-characterized apolipoproteins. Apolipoproteins A-I, C-I, and C-III-1, which also associate with the plasma high-density lipoproteins, were not degraded by serum although they were good substrates for purified thrombin and plasmin.
我们研究了人血清中存在的可消化血清淀粉样蛋白A（SAA）的蛋白酶活性。将用¹²⁵I放射性标记的SAA与血清和血浆在37℃孵育，并用碱性尿素-聚丙烯酰胺凝胶电泳和凝胶过滤色谱法分析降解产物。血清最初将SAA消化为分子量为3000 - 5000的中间体，随着孵育时间延长，这些中间体进一步降解为更小的肽段。SAA不会被用乙二胺四乙酸（EDTA）或肝素抗凝的血浆降解。用EDTA抗凝的血浆重新钙化会导致产生针对SAA的蛋白酶活性，而用凝血酶去除纤维蛋白原的EDTA血浆则无活性。我们使用了非选择性和选择性蛋白酶抑制剂以及激肽释放酶和纤溶酶的合成底物来进一步表征血清蛋白酶。这些研究表明，SAA的降解并非直接归因于参与凝血、激肽形成或纤维蛋白溶解的酶，但这种未鉴定的蛋白酶可能被一种凝血因子激活。在对三种已充分表征的载脂蛋白进行的实验中证明了SAA降解的特异性。载脂蛋白A-I、C-I和C-III-1也与血浆高密度脂蛋白相关，尽管它们是纯化的凝血酶和纤溶酶的良好底物，但不会被血清降解。
