Galactolipid formation in chloroplast envelopes. II. Isolation-induced changes in galactolipid composition.

Spinach envelopes were isolated at pH 8.5, which is inhibitory to interlipid galactosyl transfer, and at pH 7.2, which is close to values used in most recent work on chloroplast envelopes. Peptide patterns were identical, but galactolipid compositions differed markedly. These changes are such as could be explained by interlipid galactosyl transfer during isolation at pH 7.2, i.e. a strong decrease in monogalactolipid and a corresponding increase in tri- and tetragalactolipids and diacylglycerol. Digalactolipid was little affected. It was further observed that the interlipid galactosyl transfer was restricted to lipids rich in hexadecatrienoic acid. Arguments are presented that the lipid composition of envelopes in vivo is better represented by the results obtained at high pH. The results will be discussed in relation to previous data on galactolipid composition and biosynthesis in envelopes.