Synthesis of a Dicyclohexylcarbodiimide‐Binding Proteolipid by Isolated Pea Chloroplasts

Abstract

1. A proteolipid ( M r 8000) has been purified to homogeneity from pea chloroplast membranes by extraction into butan‐1‐ol. 2. The proteolipid from chloroplasts that had been incubated in the light with [ 35 S]methionine or [ 3 H]leucine gave a single radioactive band, coincident with the staining protein band, when analysed by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. 3. In washed chloroplast membranes, or in the purified state, the proteolipid covalently bound [ 14 C]dicyclohexylcarbodiimide. The reaction produced two new forms of the proteolipid, with decreased mobility in polyacrylamide gels containing dodecylsulphate. 4. On analysis by dodecylsulphate/polyacrylamide gel electrophoresis, proteolipid purified from [ 35 S]methionine‐labelled chloroplasts and treated with non‐radioactive dicyclohexylcarbodiimide gave a pattern of protein stain and radioactivity similar to that obtained when purified proteolipid was labelled with [ 14 C]dicyclohexylcarbodiimide. 5. Incorporation of radioactivity into the proteolipid, during incubation of chloroplasts with [ 35 S]methionine, occurred in the light but not in the dark and was inhibited by D (–) threo ‐chloramphenicol but not by cycloheximide or ribonuclease. We conclude that intact isolated chloroplasts from pea synthesise a dicyclohexylcarbodiimide‐binding proteolipid.