Effect of temperature on endocytosis and degradation of sulphated proteoglycans by cultured skin fibroblasts.

Temperature up to 16°C reduced endocytosis of [35S]-proteoglycans by human skin fibroblasts to less than 15% of that at 37°C. At temperatures between 20-26°C endocytosis was more than 50%. At temperatures below 26°C, the relative rate of degradation of endocytosed [35S]-proteoglycans was several fold less than the rate of endocytosis. Codistribution of endocytosed [35S]-proteoglycans and the lysosomal marker enzyme b- hexosaminidase upon subcellular fractionation indicated that endocytotic vesicles containing [35S]-proteoglycans had fused with lysosomes at 37°C and at 16°C. The prolonged halflives of endocytosed [35S]-proteoglycans at 16-26°C could not be explained merely by a temperature dependent reduction of catalytic activity of lysosomal enzymes participating in the degradation of sulphated proteoglycans.