Selman B R, Selman-Reimer S
J Biol Chem. 1981 Feb 25;256(4):1722-6.
The steady state kinetics of phenazine methosulfate-catalyzed, photosystem I-driven photophosphorylation with spinach thylakoid membranes has been measured. The Km for ADP is 85 +/- 20 microM and the Km for phosphate is 0.58 +/- 0.11 mM. Adenosine-5'-O-(thiodiphosphate) (beta-ThioADP) is a competitive inhibitor with respect to ADP at high phosphate concentrations (Kis = 105 +/- 14 microM), but is a noncompetitive inhibitor with respect to phosphate (at all ADP concentrations) and ADP at low phosphate concentrations. Thiophosphate is a competitive inhibitor with respect to phosphate (Kis = 95 +/- 9 microM), but an uncompetitive inhibitor with respect to ADP. ADP also inhibits the rate of phosphorylation at high ADP to phosphate ratios. An ordered Bi Uni mechanism with ADP preceding the binding of phosphate is proposed to explain the kinetic data.
已测定了硫酸吩嗪甲酯催化的、光系统I驱动的菠菜类囊体膜光磷酸化的稳态动力学。ADP的米氏常数为85±20微摩尔，磷酸盐的米氏常数为0.58±0.11毫摩尔。在高磷酸盐浓度下，腺苷-5'-O-(硫代二磷酸)(β-硫代ADP)是ADP的竞争性抑制剂(Kis = 105±14微摩尔)，但在低磷酸盐浓度下，它是磷酸盐(在所有ADP浓度下)和ADP的非竞争性抑制剂。硫代磷酸盐是磷酸盐的竞争性抑制剂(Kis = 95±9微摩尔)，但对ADP是反竞争性抑制剂。在高ADP与磷酸盐比例时，ADP也会抑制磷酸化速率。提出了一种有序的双底物单产物机制，其中ADP在磷酸盐结合之前，以解释动力学数据。
