Phosphorylation of glyoxysomal malate synthase from castor oil seeds Ricinus communis L.

Abstract
When glyoxysomes isolated from endosperm of 3‐day germinated Ricinus communis L. seedlings were incubated with [γ‐32P]ATP, phosphorylation of a small number of endogenous glyoxysomal proteins occurrred. A 64 kDa glyoxysomal matrix protein was predominately phosphorylated. Based upon results of immunoprecipitation, 2D‐polyacrylamide gel electrophoresis and Western blotting, the 64 kDa phosphorylated protein is identified as the subunit of malate synthase (EC 4.1.3.2). Phosphorylation of malate synthase was completed within 5 min and the amino acid residue phosphorylated was serine. Phosphorylation was inhibited by EDTA, EGTA and NaF, but enhanced by Triton X‐100.