title: A study of the in-vitro regulation of phosphoenolpyruvate carboxylase from the epidermis of Commelina communis by malate and glucose-6-phosphate.
abstract: Phosphoenolpyruvate (PEP) carboxylase activity in epidermal extracts of Commelina communis has been compared in the presence of malate and glucose-6-phosphate. The activity of PEP carboxylase was inhibited by increasing malate concentrations at several substrate (PEP) concentrations and changes in both the apparent K m (PEP) and V max values in the presence of malate suggested the occurence of mixed-type inhibiton. In the presence of glucose-6-phosphate no increase in enzyme activity was observed, although there was a slight decrease in the K m (PEP). However, glucose-6-phosphate appeared to alleviate the inhibition caused by malate. The possible implications of these properties in the control of malate production in guard cells is discussed.
authors.affiliation: Department of Biological Sciences, Faculty of Science, Plymouth Polytechnic, Drake Circus, Plymouth, Devon, UK.
authors.forename: M E
authors.initials: ME
authors.lastname: Donkin
authors.forename: J
authors.initials: J
authors.lastname: Taffs
authors.forename: E S
authors.initials: ES
authors.lastname: Martin