Autophagy-related changes of arylsulphatases A and B in rat liver lysosomes

Abstract

The total arylsulfatase activity and the relative activities of lysosomal arylsulfatase A and B [EC 3.1.6.1] were measured in the liver of control rats and rats subjected to treatments that provoke hepatic autophagocytosis. The total liver arylsulfatase activities were increased in starved and starved glucagon-treated rats, but not in sham-operated and hepatectomized rats. Arylsulfatases A and B in the mitochondrial-lysosomal (M-L) fraction were separated by polyacrylamide-gel electrophoresis at pH 8.8. They were made visible by incubating the gels with p-nitrocatechol sulfate as substrate, and measured by quantitative densitometry. In untreated controls, arylsulfatases A and B comprised 41.4 .+-. 0.5% and 58.6 .+-. 0.5% of the total arylsulfatase activity, respectively; the arylsulfatase A/arylsulfatase B activity ratio was 0.71. All experimental treatments produced a significant decrease in the percentage of lysosomal arylsulfatase present as the A form and an increase in that present as the B form, and the activity ratio of arylsulphatase A/arylsulfatase B declined. The magnitude of these changes increased in the following direction: starvation for 24 h = sham hepatectomy < glucagon + starvation < subtotal hepatectomy. The arylsulfatase A/arylsulfatase B activity ratio in liver lysosomes of normal rats is maintained within rather narrow limits, and this ratio declines during enhanced autophagocytosis. These findings, together with observations that arylsulfatase B may be a partially degraded form of arylsulfatase A, are consistent with the A form being more rapidly converted into the B form during autophagy, due to the digestive activity of other lysosomal hydrolases present in autophagic vacuoles.