Formation of sucrose from malate in germinating castor beans. I. Conversion of malate to phosphoenol-pyruvate

Abstract

Phosphoenol-pyruvic carboxylase and phospho-enol-pyruvic carboxykinase were shown to be present in castor bean extracts. When ATP was provided the conversion of oxalacetate to phosphoenol-pyruvate was strongly stimulated. Mg ion is required as a cofactor in this reaction. P32 labeled phosphoenol-pyruvate was produced when cytoplasmic particles were provided with P32-labeled phosphate and a-ketoglutarate, and C14 labeled phosphoenol-pyruvate was detected when slices of castor bean endosperm were converting malate-C14 (produced in vivo from C14O2) to sugars. The results presented support the suggestion that phosphoenol pyruvic carboxykinase is one of the enzymes involved in the conversion of malate to carbohydrate which occurs in germinating castor beans.