Effect of a Low-Sulphur-Containing Diet on Lysosomal Arylsulfatase Activity in Weanling Rats

Abstract

The effect of a low-sulphur-containing diet on the hepatic level of lysosomal arylsulfatase activity was studied in weanling rats. Weanling rats fed on a 10% soybean-protein-isolate diet, which has a low sulphur amino acid content (cystine and methionine, 1.3g and 1.4g/kg diet, respectively) about 75% that of a 10% casein diet, showed 2.0-fold increased hepatic lysosomal arylsulfatase activity (total combined activities of arylsulfatases A and B) at 3 weeks and 2.8-fold at 5 weeks, compared with those of rats maintained on an ordinary laboratory chow diet. Weanling rats fed on the casein diet showed a 1.6-fold increased in the total combined activities of arylsulfatases A and B at 5 weeks, compared with those of rats fed on the laboratory chow diet. These increases were suppressed by addition of cystine or methionine to the soybean-protein-isolate diet. On the other hand, liver lysosomal arylamidase activities were not altered significantly by either diet. Therefore, the elevated lysosomal arylsulfatase activities in liver of rats fed on the soybean-protein-isolate diet might be attributable to insufficiency of sulphur-containing amino acids in the diet. The elevation of arylsulfatase activities was not due to changes in arylsulfatase-specific mRNA, as revealed by Northern blot and slot-blot hybridization analysis, since the changes in mRNA content were only marginal. We conclude that induction of lysosomal arylsulfatase activity by a soybean-protein-isolate diet is brought about by an increase in the amount of translation of arylsulfatase mRNA.