Na K J, Lee H J
Arch Biochem Biophys. 1983 Dec;227(2):580-6. doi: 10.1016/0003-9861(83)90487-3.
The nature of chloride ion as an activator of angiotensin-converting enzyme was studied by a series of kinetic experiments with hog plasma enzyme preparation. The enzyme required the presence of chloride ion for its full catalytic activity, but its requirement of monovalent anion was not absolute. The KA value for the enzyme-chloride binding was estimated to be about 150 mM in all cases regardless of the peptide substrates employed. In the presence of chloride ion, the activity of the enzyme was increased, but its optimum pH was shifted gradually to the alkaline region up to pH 8.2 depending on the concentration of chloride ion. In addition, in the presence of chloride ion, the apparent Km values were reduced markedly while the Vmax values were not much altered; for example, for the hydrolysis of angiotensin I decapeptide, the Km value decreased by a factor of 50 while only an 18% increase in Vmax was observed when the enzyme was saturated with chloride ion. The result suggests that chloride ion acts as a conformational modifier inducing the affinity of synergistic binding of substrate.
通过对猪血浆酶制剂进行一系列动力学实验，研究了氯离子作为血管紧张素转换酶激活剂的性质。该酶需要氯离子的存在才能发挥其全部催化活性，但其对单价阴离子的需求并非绝对。无论使用何种肽底物，在所有情况下酶与氯离子结合的KA值估计约为150 mM。在氯离子存在下，酶的活性增加，但其最适pH值根据氯离子浓度逐渐向碱性区域移动，直至pH 8.2。此外，在氯离子存在下，表观Km值显著降低，而Vmax值变化不大；例如，对于血管紧张素I十肽的水解，当酶被氯离子饱和时，Km值降低了50倍，而Vmax仅增加了18%。结果表明，氯离子作为一种构象修饰剂，诱导底物协同结合的亲和力。
