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

The cell-free extract from leaves of Sedum mexicanum, a typicalCAM plant, formed ¹⁴C-malate from ¹⁴C-aspartate in the presenceof NAD. No reduction of NAD was observed during the reaction.Analysis of this reaction revealed that the transfer of labelfrom ^l4C-aspartate to malate takes place by the action of malatedehydrogenase and aspartate aminotransferase, and the reactionwas reversible in model experiments with commercial enzymes.Pitfalls in assessing data on dark ¹⁴CO₂ fixation in CAM arediscussed with reference to the transfer of label between malateand aspartate without actual synthesis. (Received June 2, 1979; )