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Plant Physiology 91:954-960 (1989)
© 1989 American Society of Plant Biologists

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Metabolism and Enzymology

Malate-Induced Hysteresis of Phosphoenolpyruvate Carboxylase from Crassula argentea1

Apinya Ngam-ek, Thomas A.P. Seery, Eric J. Amis and Scott D. Grover

Department of Chemistry and Biochemistry, California State University, Los Angeles, California 90032, Department of Chemistry, University of Southern California, Los Angeles, California 90089

The hysteretic behavior of phosphoenolpyruvate (PEP) carboxylase from Crassula argentea has been investigated. Incubation of the purified enzyme with the inhibitor malate prior to starting the reaction by the addition of PEP resulted in a kinetic lag of several minutes duration. The length of the lag was inversely proportional to the enzyme concentration, suggesting subunit association-dissociation as the hysteretic mechanism, rather than a mechanism based on a slow conformational change in the enzyme. Dynamic laser light scattering measurements also support this conclusion, showing that the diffusion coefficient of malate-incubated enzyme slowly decreased after the reaction was started by the addition of PEP. Lags were observed only at pH values of 7.5 or lower. Maximum lags were observed after 10 min of preincubation with malate. Fumarate and succinate, which like malate caused mixed inhibition, also caused lags. In contrast, no lag was induced by malate in the presence of PEP or by the competitive inhibitor phosphoglycolate. The activators glucose 6-phosphate and malonate decreased the malate-induced lag.

1 Supported in part by Public Health Service grant RR-08101 from the MBRS program, Division of Research Resources, National Institutes of Health and grant DMB-8707046 from the National Science Foundation.






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