Metabolism of the Plant Sulfolipid-Sulfoquinovosyldiacylglycerol: Degradation in Animal Tissues

Metabolism of the plant sulfolipid—sulfoquinovosyldiacylglycerol (SQDG)—was studied in animal tissues. In vivo experiments with $[^{35}S]$SQDG in guinea pigs showed that this lipid is not absorbed intact in the gastrointestinal tract. In these experiments, 3 h after administration of $[^{35}S]$SQDG, the intestinal mucosa contained 1 to 5% of the radioactivity as SQDG, while the remainder was in a water-soluble form. Analysis of the water-soluble components showed that about 60% of the radioactivity was present as sulfoquinovosylglycerol (SQG) and the remainder was present as free $SO^{2−}_4$. In the blood, 99% of the radioactivity was present as $SO^2_4$, SQG was not observed. In liver, only very little radioactivity was observed and appeared to be mainly in the form of $SO^{2−}_4$. Experiments with everted intestinal sacs of guinea pigs confirmed the formation of SQG, $SO^{2−}_4$, and, in addition, sulfoquinovosylmonoacylglycerol (SQMG) in this tissue. In vitro experiments with saline extracts of acetone powders of pancreas and intestinal mucosa of guinea pig, sheep, and rat showed that $[^{35}S]$SQDG was deacylated to SQMG (sulfolipase A activity) and SQG (sulfolipase B activity). It is concluded that animal tissues deacylate SQDG in a stepwise manner to SQG. It is further metabolized to yield free $SO^{2−}_4$ by cleavage of the C-S bond which appears to be brought about by the intestinal microflora. Sheep pancreatic sulfolipases were characterized. Bile salts, sodium dodecyl sulfate, and Triton X-100 inhibited the pancreatic sulfolipases, while $CaCl_2$ activated them. Substrate competition experiments and investigations on substrate specificity with a partially purified preparation indicated that relatively specific sulfolipase(s) may exist in pancreas. Among the species tested, guinea pig tissues showed the highest sulfolipase A and B activities followed sheep and rat tissues. Pancreatic enzymes were 18 to 60 times more active than intestinal enzymes