Transfer of label from aspartate to malate by the cell-free extract of Sedum mexicanum leaves

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Abstract
The cell-free extract from leaves of Sedum mexicanum, a typical CAM plant, formed 14C-malate from 14C-aspartate in the presence of NAD. No reduction of NAD was observed during the reaction. Analysis of this reaction revealed that the transfer of label from l4C-aspartate to malate takes place by the action of malate dehydrogenase and aspartate aminotransferase, and the reaction was reversible in model experiments with commercial enzymes. Pitfalls in assessing data on dark 14CO2 fixation in CAM are discussed with reference to the transfer of label between malate and aspartate without actual synthesis.