Kinetics of Formation and Dissociation of Metallocarboxypeptidases

E.J. Billo, K.K. Brito, R.G. Wilkins
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引用次数: 19

Abstract

The rates of formation of a number of metallocarboxypeptidases from metal ions and bovine apocarboxypeptidase A (CPA) have been measured directly and by a competitive method. Rates were determined within pH = 6–8 by utilising the pH change attending metal-ion incorporation, employing indicator and stopped-flow. Second-order rate constants (kf, M−1 s−1 at 25°C, I = 1 M NaCl, pH = 7, Tris = 25 μM) were 1.7 × 105 (Mn2+), 3 × 104 (Co2+), 5 × 103 (Ni2+), 7 × 105 (Zn2+), and 9 × 105 (Cd2+). Relative incorporation rate constants were determined at 25°, pH = 7.0, Tris = 0.1 M, by competing two metal ions for a deficiency of apoprotein and analyzing the products by differential enzyme activity. Agreement between the two methods was reasonable. Rate constants for dissociation of CoCPA, NiCPA, and ZnCPA were measured by loss of enzyme activity on addition of the metal ion scavenger EDTA. Values of kd at 25°, I = 1.0 M NaCl, pH = 7.0 were 8 × 10−3, 3 × 10−5, and 4 × 10−4 s−1, respectively, Values of K obtained kinetically (kf/kd) were in good agreement with those determined by activity measurements of equilibrated solutions. Results are compared with those of bovine apocarbonic anhydrase, where generally significantly slower rates are encountered.

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金属羧肽酶的形成和解离动力学
本文用竞争法直接测定了金属离子与牛伪羧基肽酶a (CPA)合成金属羧基肽酶的速率。在pH = 6-8范围内,利用金属离子掺入引起的pH变化,采用指示剂和停流来测定速率。二阶速率常数(kf, M−1 s−1,25℃,I = 1 M NaCl, pH = 7, Tris = 25 μM)分别为1.7 × 105 (Mn2+), 3 × 104 (Co2+), 5 × 103 (Ni2+), 7 × 105 (Zn2+)和9 × 105 (Cd2+)。在25°,pH = 7.0, Tris = 0.1 M条件下,通过两种金属离子竞争载脂蛋白缺失,并通过差异酶活性分析产物,确定了相对掺入速率常数。两种方法的一致性是合理的。CoCPA、NiCPA和ZnCPA的解离速率常数是通过添加金属离子清除剂EDTA时酶活性的损失来测定的。在25°、I = 1.0 M NaCl、pH = 7.0条件下,kd值分别为8 × 10−3、3 × 10−5和4 × 10−4 s−1,动力学得到的K值(kf/kd)与平衡溶液活度测量结果吻合较好。结果与牛脱碳酸酐酶的结果进行了比较,后者的速率通常要慢得多。
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Chapter III. Complexes containing carbon monoxide: synthesis, reactivity, structure, bonding and therapeutic aspects of carbon monoxide–releasing molecules (CORMs) in human beings and plants Frontmatter Chapter IV Advantageous role of gaseous signalling molecule, H2S: hydrogen sulphide and their respective donors, in ophthalmic diseases and physiological implications in plants Chapter I. Coordination chemistry of chlorophylls/ bacteriochlorophylls and its functional aspects in photosynthesis Index
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