Katewa Subhash D, Katyare Surendra S
Department of Biochemistry, Faculty of Science, M. S. University of Baroda, Vadodara, 390 002, India.
Indian J Biochem Biophys. 2003 Aug;40(4):252-9.
The kinetic properties of the rat liver microsomal ATPase, with respect to Na(+), K(+) and AT P requirements were examined. Presence of Na(+) and K(+), or both hardly caused any stimulation of the enzyme activity. The Km values for Na(+) and K(+) were substantially low (0.32 and 0.05 mM, respectively), compared to those reported for the Na(+), K(+) ATPasesfrom different tissues. Substrate kinetics studies revealed that in the absence of Na(+) and K(+), ATP is an activator of the enzyme. The enzyme displayed increased activity with increase in the energy of activation in the absence of Na(+) and K(+). The activity was partially inhibited by ouabain only in the presence of Na(+) and K(+). The results suggest that the liver microsomal enzyme is not a Na(+), K(+) ATPase, but has requirement of monovalent cations for the regulation of its activity. Also, the beta3 subunit of the enzyme has a Km lowering effect.
研究了大鼠肝微粒体ATP酶在钠、钾和ATP需求方面的动力学特性。钠和钾或两者的存在几乎不会对酶活性产生任何刺激。与不同组织中报道的钠钾ATP酶相比，钠和钾的米氏常数相当低（分别为0.32和0.05 mM）。底物动力学研究表明，在没有钠和钾的情况下，ATP是该酶的激活剂。在没有钠和钾的情况下，随着激活能的增加，该酶的活性增强。只有在存在钠和钾的情况下，哇巴因才会部分抑制该活性。结果表明，肝微粒体酶不是钠钾ATP酶，但需要单价阳离子来调节其活性。此外，该酶的β3亚基具有降低米氏常数的作用。
