Galactosylation of different monogalactosyldiacylglycerols by cell-free preparations from pea leaves.

The formation of digalactosyldiglycerol (DGD) from monogalactosyldiglycerol (MDG) was studied in cell-free preparations from pea leaves. Under optimized conditions UDP-[U-14C]galactose was incorporated into a single lipid which was shown to be DGD by cochromatography before and after deacylation and by cocrystallization of the acetyl derivative. Seven MGD species were prepared which had different fatty acids and from zero to eight double bonds. These substrates were dispersed at identical overall concentrations by sonication in Triton X-100 solution and galactosylation rates were measured under optimized conditions. Galactosylation rates increased with the number of double bonds up to a total of six, beyond which the rate decreased again. These galactosylation rates cannot be related to difference in the diglyceride moieties of natural MGD and DGD.