Sakai H, Suzuki K, Imahori K
J Biochem. 1986 Apr;99(4):1157-67. doi: 10.1093/oxfordjournals.jbchem.a135579.
Pyruvate kinase was purified to homogeneity from a moderate thermophile, Bacillus stearothermophilus. The molecular weight of the enzyme was found to be 250,000 on gel filtration and 242,000 on sedimentation analysis. The enzyme consisted of four identical subunits of a molecular weight of 62,000-64,000. There were no remarkable differences between the thermophilic enzyme and mesophilic enzymes in amino acid composition, secondary structure, mono- and di-valent cation requirements for activity or specificity for nucleoside diphosphates. But the thermophilic enzyme was stable at high temperature and for a longer period of storage at lower temperature. Its specific activity was relatively high even at a low temperature (30 degrees C). The enzyme exhibited homotropic positive cooperativity for phosphoenol-pyruvate, but not for ADP. It was allosterically activated by AMP, ribose 5-phosphate and nucleoside monophosphates, but not by fructose 1,6-bisphosphate. Activation by AMP and ribose 5-phosphate, and inhibition by inorganic phosphate were also observed even at the physiological temperature (60 degrees C) for the thermophile.
丙酮酸激酶是从嗜热脂肪芽孢杆菌这种中度嗜热菌中纯化至同质的。通过凝胶过滤法测得该酶的分子量为250,000，沉降分析法测得为242,000。该酶由四个分子量为62,000 - 64,000的相同亚基组成。嗜热酶与嗜温酶在氨基酸组成、二级结构、活性所需的一价和二价阳离子以及对核苷二磷酸的特异性方面均无显著差异。但嗜热酶在高温下稳定，且在低温下能储存更长时间。即使在低温（30摄氏度）下，其比活性也相对较高。该酶对磷酸烯醇丙酮酸表现出同向正协同性，但对ADP则不然。它受到AMP、5 - 磷酸核糖和核苷单磷酸的变构激活，但不受1,6 - 二磷酸果糖激活。即使在嗜热菌的生理温度（60摄氏度）下，也观察到了AMP和5 - 磷酸核糖的激活作用以及无机磷酸盐的抑制作用。
