Synthesis of Proteins by Isolated Euglena gracilis Chloroplasts

Abstract

Intact Euglena gracilis chloroplasts, which had been purified on gradients of silica sol, incorporated [(35)S]methionine or [(3)H]leucine into soluble and membrane-bound products, using light as the only source of energy. The chloroplasts were osmotically shocked, fractionated on discontinuous gradients of sucrose, and the products of protein synthesis of the different fractions characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The soluble fraction resolved into three zones of radioactivity, the major one corresponding to the large subunit or ribulose diphosphate carboxylase. The thylakoid membrane fraction contained nine labeled polypeptides, the two most prominent in the region of 31 and 42 kilodaltons. The envelope fraction contained a major radioactive peak of about 48 kilodaltons and four other minor peaks. The patterns of protein synthesis by isolated Euglena chloroplasts are broadly similar to those observed with chloroplasts of spinach and pea.