Biochemical evidence for an endocytically inactive population of lysosomes

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Abstract
The peroxidase dependent, diaminobenzidine (DAB) density shift procedure was applied to the characterization of lysosomes from Chinese hamster ovary (CHO) cells. Peroxidase activity was localized in lysosomes by a 15-18 h internalization period. After treatment with DAB, the distribution of peroxidase activity in Percoll gradients was shifted, as a population, to a higher density. A bimodal distribution which included a low density population was observed for the native lysosomal enzyme .beta.-hexosaminidase after DAB treatment. A second lysosomal enzyme, .alpha.-fucosidase, was strongly inhibited by DAB treatment with the residual activity corresponding in distribution to the light .beta.-hexosaminidase population. The occurrence of a low density lysosomal population after the DAB procedure suggests the existence of an endocytically inactive lysosomal population in fibroblasts. Probable physiological candidates for such a population are discussed.