Tu S I, Sliwinski B J
Arch Biochem Biophys. 1985 Sep;241(2):348-55. doi: 10.1016/0003-9861(85)90556-9.
The kinetics of corn root plasma membrane-catalyzed Mg-ATP hydrolysis may be satisfactorily described by a simple Michaelis-Menten scheme. It was found that the Km of the process was relatively insensitive to changes in temperature. This property allowed us to conveniently estimate the activation energy of the enzyme turnover process as approximately 14 kcal mol-1 in the temperature range of 10 to 45 degrees C. The enzyme activity was inhibited by the presence of diethystilbestrol (DES), miconazole, vanadate, and dicyclohexylcarbodiimide (DCCD). The inhibition caused by DES and miconazole was strictly uncompetitive and inhibition by vanadate was noncompetitive. The inhibition by DCCD showed a substrate concentration dependence, i.e., competitive at high and uncompetitive at low concentrations of Mg-ATP. The 1/V vs [I] plots suggested that there were different but unique binding sites for DES, vanadate, and miconazole. However, the modification of the plasma membrane by DCCD exhibited interaction with multiple sites. Unlike yeast plasma membrane ATPase, the enzyme of corn root cells was not affected by the treatment with N-ethylmaleimide. Although the enzyme activity was regulated by ADP, a product of the reaction, the presence of inorganic phosphate showed no inhibition to the hydrolysis of Mg-ATP.
玉米根细胞质膜催化的Mg-ATP水解动力学可以用简单的米氏方程得到满意的描述。研究发现，该过程的米氏常数（Km）对温度变化相对不敏感。这一特性使我们能够方便地估算出在10至45摄氏度温度范围内酶周转过程的活化能约为14千卡/摩尔。己烯雌酚（DES）、咪康唑、钒酸盐和二环己基碳二亚胺（DCCD）的存在会抑制该酶的活性。DES和咪康唑引起的抑制作用是严格的非竞争性抑制，钒酸盐引起的抑制作用是非竞争性抑制。DCCD引起的抑制作用表现出底物浓度依赖性，即在高浓度Mg-ATP时为竞争性抑制，在低浓度时为非竞争性抑制。1/V对[I]作图表明，DES、钒酸盐和咪康唑存在不同但独特的结合位点。然而，DCCD对质膜的修饰表现出与多个位点的相互作用。与酵母质膜ATP酶不同，玉米根细胞的该酶不受N-乙基马来酰亚胺处理的影响。尽管酶活性受反应产物ADP的调节，但无机磷酸盐的存在对Mg-ATP的水解没有抑制作用。
