Department of Biology, University of Patras, Patras, Greece.
Plant Physiol. 1985 Feb;77(2):300-2. doi: 10.1104/pp.77.2.300.
Photoactivation of phosphoenolpyruvate carboxylase in C(4) plants is detected more efficiently when activity is assayed at suboptimum pH (e.g. 7.2); the magnitude of the light effect is often larger at low phosphoenolpyruvate concentration.Darkness and low assay pH induce an allosteric behavior (positive cooperativity with phosphoenolpyruvate) which is relieved in light or by higher pH; thus, normal Michaelis-Menten kinetics are exhibited only when the enzyme is extracted during the day and assayed at pH 8.2.Light activation, pH, and substrate level appear to be components of a regulatory device suppressing the activity in darkness and enhancing it under light.
在 C(4) 植物中,当在亚最佳 pH(例如 7.2)下测定时,磷酸烯醇丙酮酸羧化酶的光激活更容易被检测到;在低磷酸烯醇丙酮酸浓度下,光效应的幅度通常更大。黑暗和低测定 pH 值诱导变构行为(与磷酸烯醇丙酮酸的正协同作用),这种作用在光照或更高 pH 值下得到缓解;因此,只有当酶在白天提取并在 pH 8.2 下测定时,才会表现出正常的米氏动力学。光激活、pH 值和底物水平似乎是一种调节装置的组成部分,该装置在黑暗中抑制酶的活性,在光照下增强其活性。