Carbohydrate mediated recognition of lysosomal enzymes by cell surface receptors.

The recognition of lysosomal enzymes by various carbohydrate specific cell surface receptors is reviewed. In particular the biosynthesis of mannose 6-phosphate residues in lysosomal enzymes and their role for targeting of lysosomal enzymes to lysosomes are discussed.

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.