Acid Metabolism in Atriplex II. Oxalate Synthesis During Acid Metabolism in the Dark

Abstract

Malate and aspartate, labelled in the C-4 position, were the only stable products of short-term dark 14C02 fixation in Atriplex spongiosa leaves. Label was subsequently transferred to citrate, glutamate, and other amino acids. Oxalate was slowly labelled during dark fixation and was a major labelled product after 18 hr. The accumulation of label in oxalate and other acids was inhibited by 20 Mm malonate suggesting that oxalate stemmed from tricarboxylic acid cycle intermediates. Oxalate was slowly labelled during metabolism of [U-14C]glucose and [1,5- 14C]citrate, but [1_14C]glyoxylate was readily oxidized to oxalate. These data are consistent with oxalate production from glyoxylate derived from isocitrate during dark acid metabolism. Phosphoenol pyruvate carboxylase, isocitrate lyase, and glycolate oxidase activity in cell-free extracts of A. spongiosa leaves provided further evidence for this pathway.