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Estimation of pyruvate,phosphate dikinase activity in maize leaf tissue by (phosphoenolpyruvate plus pyrophosphate)-dependent phosphorylation of AMP
Authors:Colin G. Hocking  John W. Anderson
Affiliation:Botany Department, La Trobe University, Bundoora, Victoria 3083, Australia
Abstract:
Crude extracts of maize leaf tissue catalysed the phosphorylation of AMP by 32PPi in the presence of phosphoenolpyruvate (PEP). The reaction was enhanced by F? and NH4+. The optimum concentrations of AMP, PEP and PPi were 0.3, 10 and 1 mM, respectively. Under these conditions, ca75% of the AMP phosphorylated by 32PPi was present as ATP and ca25 % as ADP. The activity was reversibly cold labile. The specific activity of crude extracts in the presence of F? was proportional to enzyme concentration only at protein concentrations < 25,μg/ml. Partially purified pyruvate, phosphate dikinase (PPD) from maize leaf quantitatively phosphorylated AMP to ATP in a (PEP plus PPi)-dependent reaction with the concomitant production of 0.9 mol of pyruvate per mol of AMP phosphorylated. It was concluded that (PEP plus PPi)-dependent phosphorylation of AMP provides a reliable method for estimating PPD activity in crude extracts of maize. Crude maize extracts also catalysed 32Pi-ATP and 32PPi-ATP exchange but these activities were not specific for PPD.
Keywords:Gramineae  maize  pyruvate  phosphate dikinase  pyrophosphate metabolism  phosphorylation of AMP  phosphoenolpyruvate metabolism  pyruvate metabolism.
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