Formation of Oxalacetate and Aspartate from Phospho-Enol-Pyruvate in Spinach Leaf Chloroplast Extract

Abstract

WHILE investigating the ability of water extracts¹ of spinach leaf chloroplasts to catalyse ‘dark’ carb-oxylation reactions, we have found that the addition of phospho-enol-pyruvate and ¹⁴CO₂ to the colourless chloroplast extract causes the accumulation of labelled oxalacetate and labelled aspartate in the reaction mixture. Bandurski and Greiner² using spinach leaves, Tchen and Vennesland³ using wheat germ and spinach leaves, and Utter et al. ⁴ using bird liver, have described enzyme preparations which catalyse irreversible and reversible carboxylations of phospho-enol-pyruvate to oxalacetate. The formation of oxalacetate in our experiments indicates the presence of a phospho-enol-pyruvate carboxylase in the chloroplast. Aspartate can then be formed by transamination of oxalacetate. The rate of carbon fixation was increased when, in addition to phospho-enol-pyruvate, either alanine, glutamine or aspartic acid was added to the reaction mixture.