Ivanova K, Heim J M, Gerzer R
Labor. für klinische Pharmakologie, Medizinische Klinik Innenstadt der Universität, München, F.R.G.
Eur J Pharmacol. 1990 Oct 30;189(4-5):317-26. doi: 10.1016/0922-4106(90)90125-h.
The present investigation describes kinetic characteristics of membrane-bound and Triton X-100-solubilized atrial natriuretic factor (ANF)-sensitive guanylate cyclase from bovine adrenal cortex. The kinetic analysis of both enzyme forms suggests that in the presence of manganese, ANF induces or stabilizes at least two apparent GTPMn2(+)- and in addition two Mn2(+)-binding sites. Addition of the natriuretic drug amiloride favors this state. ATP increases the vmax in the presence of ANF for GTPMg2+, but not for GTPMn2+ as a substrate. With GTPMg2+, amiloride has no effect on basal or ANF-stimulated activity, but slightly reduces the effect of ATP. Under all conditions tested, the enzyme follows regular Michaelis-Menten kinetics in the presence of Mg2+ and exhibits positive cooperativity with Mn2+. Positive cooperativity is also retained after Triton extraction. The results indicate that Triton extraction has no major influence on the kinetic properties of particulate guanylate cyclase when the extraction procedure is done carefully. The data also support the suggestion that multiple interactions of subunits might occur upon activation of the enzyme by ANF in the presence of Mn2+.
本研究描述了来自牛肾上腺皮质的膜结合型和经曲拉通X-100增溶的心房利钠因子（ANF）敏感型鸟苷酸环化酶的动力学特性。对这两种酶形式的动力学分析表明，在锰存在的情况下，ANF诱导或稳定了至少两个明显的GTPMn2(+)结合位点，此外还有两个Mn2(+)结合位点。添加利钠药物氨氯地平有利于这种状态。ATP在存在ANF的情况下会增加以GTPMg2+为底物时的最大反应速度，但对以GTPMn2+为底物时则无此作用。对于GTPMg2+，氨氯地平对基础活性或ANF刺激的活性没有影响，但会略微降低ATP的作用。在所有测试条件下，该酶在Mg2+存在时遵循常规的米氏动力学，并且与Mn2+表现出正协同性。经曲拉通提取后，正协同性也得以保留。结果表明，当小心进行提取过程时，曲拉通提取对颗粒状鸟苷酸环化酶的动力学性质没有重大影响。这些数据还支持这样的观点，即在锰存在的情况下，ANF激活酶时亚基之间可能会发生多种相互作用。
