This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (23) Citing Articles via Google Scholar Google Scholar Articles by Wedding, R. T. Articles by Black, M. K. Search for Related Content PubMed PubMed Citation Articles by Wedding, R. T. Articles by Black, M. K. Agricola Articles by Wedding, R. T. Articles by Black, M. K.

Metabolism and Enzymology

Kinetic Studies of the Form of Substrate Bound by Phosphoenolpyruvate Carboxylase ¹

Department of Biochemistry, University of California, Riverside, California 92506

Phosphoenolpyruvate carboxylase isolated from maize (Zea mays L.) leaves was assayed with varying concentrations of free phosphoenolpyruvate at several fixed-varying concentrations of free magnesium higher than required to saturate the enzyme reaction. These assays produced velocity data which were found to form a family of individual lines when plotted against free phosphoenolpyruvate or against total phosphoenolpyruvate, but not when plotted against the concentration of the complex of phosphoenolpyruvate with magnesium. In this latter case, the points from all the fixed-varying concentrations fell on the same line, which can be fitted to a modified Michaelis-Menten equation with a multiple correlation coefficient R² = 0.995. Similar results were obtained when the enzyme from the C₄ plant maize was assayed with manganese rather than magnesium and when phosphoenolpyruvate carboxylase from leaves of the C₃ plant wheat (Triticum vulgare Vill.) was assayed with magnesium. However, at pH 7.0 the enzyme from the Crassulacean acid metabolism plant Crassula argentea did not produce a satisfactory single line when plotted against the complex of metal ion and substrate, but did so when the assay pH was raised to 8.0. It is concluded that in general the preferred form of substrate for phosphoenolpyruvate carboxylase is the complex of phosphoenolpyruvate with the metal ion.

¹ Supported in part by National Science Foundation grant PCMB 85-15181.

This article has been cited by other articles:

				A. Tovar-Méndez, C. Mújica-Jiménez, and R. A. Muñoz-Clares Physiological Implications of the Kinetics of Maize Leaf Phosphoenolpyruvate Carboxylase Plant Physiology, May 1, 2000; 123(1): 149 - 160. [Abstract] [Full Text]