H. Miziorko, H. Miziorko, Thomas Nowak
Jul 1, 1974
Citations
1
Influential Citations
68
Citations
Quality indicators
Journal
Archives of biochemistry and biophysics
Abstract
Abstract Spinach leaf phosphoenolpyruvate carboxylase has been purified to homogeneity using salt fractionatjon, chromatography, and immunologie procedures to remove contaminating ribulose diphosphate carboxylase. From gel filtration and isoelectric focusing, the molecular weight (~560,000) and isoelectric point (pI = 4.9) are indistinguishable from those of ribulose diphosphate carboxylase. The subunit molecular weight of phosphoenolpyruvate carboxylase (130,000) suggests that the native enzyme is a tetramer. Kinetic studies using Mg2+ or Mn2+ as the activator indicate that the divalent cation lowers the Km of the substrate phosphoenolpyruvate by an order of magnitude and conversely, that the presence of the substrate similarly lowers the Km of the metal ion, suggesting an enzyme-metal-substrate bridge complex. Three analogs of phosphoenolpyruvate, l phospholactate, d -phospholactate, and phosphoglycolate are potent competitive inhibitors. The inhibitor constant (Ki) of l -phospholactate (2 μ m ) is 49-fold lower with Mn2+ as the activator than with Mg2+. An analysis of the competitive inhibition by portions of the l -phospholactate molecule (i.e., l -lactate, methyl phosphate, and phosphite) indicates this 49-fold lowering is due to increased interaction of the phosphoryl group and, to a lesser extent, of the carboxyl and C-O-P bridge oxygen of l -phospholactate with the enzyme metal complex. The results provide indirect evidence for phosphoryl coordination by the enzyme-bound divalent cation.