Lopina O D, Sarvazyan N A, Askari A, Boldyrev A A
Department of Biochemistry, School of Biology, Moscow State University, Russia.
Arch Biochem Biophys. 1995 Aug 20;321(2):429-33. doi: 10.1006/abbi.1995.1414.
Highly purified preparations of duck salt gland and canine kidney Na+/K(+)-ATPases with comparable specific activities were used to clarify the causes of previously reported differences between the substrate-velocity curves of these enzymes. When assays were done under identical conditions (pH 7.4; 37 degrees C), and a wide range of closely spaced ATP concentrations were used, the curves of both enzymes exhibited intermediary plateaus, as noted before for the salt gland enzyme. The two enzymes also had the same numbers of phosphorylation and ouabain binding sites, and their catalytic subunits were of the alpha 1 isoform type as revealed by immunostaining with specific antibodies. The findings suggest that the substrate-velocity curves of all widely used Na+/K(+)-ATPases may contain an intermediary plateau which is diagnostic of reaction mechanisms that generate rate equations containing powers of substrate concentration greater than two, e.g., a mechanism involving an oligomer with more than two protomers.
使用具有可比比活性的鸭盐腺和犬肾Na+/K(+)-ATP酶的高度纯化制剂，以阐明先前报道的这些酶底物-速度曲线之间差异的原因。当在相同条件下（pH 7.4；37℃）进行测定，并使用广泛的紧密间隔的ATP浓度时，两种酶的曲线均显示出中间平台，如之前盐腺酶所观察到的那样。两种酶还具有相同数量的磷酸化和哇巴因结合位点，并且如用特异性抗体免疫染色所揭示的，它们的催化亚基为α1同工型。这些发现表明，所有广泛使用的Na+/K(+)-ATP酶的底物-速度曲线可能都包含一个中间平台，这是反应机制的诊断指标，该反应机制产生的速率方程包含大于二的底物浓度幂次，例如，涉及具有两个以上原体的寡聚体的机制。
