Uridine-diphospho-sulfoquinovose: diacylglycerol sulfoquinovosyltransferase activity is concentrated in the inner membrane of chloroplast envelopes

Abstract

In experiments on the assembly of the sulfolipid sulfoquinovosyl diacylglycerol in envelope membranes of chloroplasts, UDP-sulfoquinovose (UDPS) was used with highest efficiency, and the corresponding enzyme, UDP-sulfoquinovose:diacylglycerol sulfoquinovosyltransferase, was partially characterized (E. Heinz et al., 1989, Eur J Biochem 184: 445–453). Here, we identified 35S- and 33P-labelled UDPS from various photosynthetically active organisms, suggesting that the sulfosugar nucleotide used for sulfolipid biosynthesis throughout the plant kingdom, including phototrophic bacteria, may indeed be UDPS. For attribution of the 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 envelopes, 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.