大鼠心脏腺苷激酶的特性
Properties of rat heart adenosine kinase.
作者信息
Fisher M N, Newsholme E A
出版信息
Biochem J. 1984 Jul 15;221(2):521-8. doi: 10.1042/bj2210521.
Adenosine kinase was purified 870-fold from rat heart by a combination of gel filtration and affinity chromatography. The preparation was free of purine-metabolizing enzymes that could interfere in the assay of the kinase. A study of the properties of the purified enzyme showed that it is activated by Na+ and K+, it possesses a broad pH optimum between 6 and 8, MgATP is the nucleotide substrate, free Mg2+ is an inhibitor with respect to both MgATP and adenosine, and the enzyme is subject to substrate inhibition by adenosine. The severity of this inhibition increases as the concentration of free Mg2+ increase. The Km for MgATP was calculated to be 0.8 mM and that for adenosine, at likely physiological concentrations of MgATP and free MgCl2, was about 0.2 microM. In vivo the enzyme is likely to be saturated with both MgATP and adenosine. Indeed, the adenosine concentration in rat heart in vivo is probably sufficient to cause substrate inhibition, and this would be increased by an increase in free Mg2+ concentration. Changes in the concentrations of adenosine and free Mg2+ may play a role in modifying the activity of the enzyme in vivo.
通过凝胶过滤和亲和层析相结合的方法，从大鼠心脏中纯化出腺苷激酶，纯化倍数达870倍。该制剂不含可干扰激酶测定的嘌呤代谢酶。对纯化酶性质的研究表明，它被Na⁺和K⁺激活，在6至8之间具有较宽的最适pH值，MgATP是核苷酸底物，游离Mg²⁺对MgATP和腺苷均为抑制剂，且该酶受到腺苷的底物抑制。随着游离Mg²⁺浓度的增加，这种抑制的严重程度也增加。MgATP的Km值经计算为0.8 mM，在MgATP和游离MgCl₂的可能生理浓度下，腺苷的Km值约为0.2 μM。在体内，该酶可能被MgATP和腺苷饱和。实际上，大鼠心脏中体内腺苷浓度可能足以引起底物抑制，而游离Mg²⁺浓度的增加会加剧这种抑制。腺苷和游离Mg²⁺浓度的变化可能在体内调节该酶的活性中起作用。
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