URIDINE-DIPHOSPHO-SULFOQUINOVOSE - DIACYLGLYCEROL SULFOQUINOVOSYLTRANSFERASE ACTIVITY IS CONCENTRATED IN THE INNER MEMBRANE OF CHLOROPLAST ENVELOPES

In experiments on the assembly of the sulfolipid sulfoquinovosyl diacy lglycerol in envelope membranes of chloroplasts, UDP-sulfoquinovose (U DPS) was used with highest efficiency, and the corresponding enzyme, U DP-sulfoquinovose:diacylglycerol sulfoquinovosyltransferase, was parti ally characterized (E. Heinz et al., 1989, Fur J Biochem 184. 445-453) . Here, we identified S-35- and P-33-labelled UDPS from various photos ynthetically active organisms, suggesting that the sulfosugar nucleoti de used for sulfolipid biosynthesis throughout the plant kingdom, incl uding phototrophic bacteria: may indeed be UDPS. For attribution of th e sulfolipid synthase to one of the two plastidial envelope membranes, these membranes were isolated from pea and spinach chloroplasts. The sulfoquinovosyltransferase was localized in the inner membrane of enve lopes, which also contains the competing UDP-galactose:diacylglycerol galactosyltransferase. In contrast to the sulfoquinovosyltransferase, a substantial proportion of the galactosyltransferase was found in the outer membranes of envelopes from pea chloroplasts.