Fibroblast galactosidase assimilation

Evidence has been obtained that supports the suggestion of Kaplan, Achord, and Sly (35) that phosphate residues contribute to the assimilation of lysosomal enzymes by fibroblasts. The strong inhibition of 6-galactosidase assimilation by mannose-6-phosphate may not be explained solely on the basis of the compound s mannose content. Experiments in our laboratories designed to detect the presence of mannose-6-phosphate in e-galactosidase have demon-... 

Several laboratories have studied the assimilation of specific lysosomal enzymes using as model systems skin fibroblasts deficient in the enzyme under study. The underlying mechanism for the translocation of lysosomal enzymes was hypothesized to involve binding of carbohydrate-containing recognition markers to specific cell surface receptors (1 5). In support of this hypothesis Hickman, Shapiro, and Neufeld (16J found that treatment of N-acetyl-B-hexosaminidase with periodate under conditions that dTd not affect enzymatic activity prevented the efficient assimilation of this enzyme by Sandhoff fibroblasts. Additionally, Kresse and von Figura (1 7) found that treatment of f -acetyl-a-hexosaminidase with B-galactosidase reduced the assimilation of this enzyme by San-filippo B fibroblasts. 

Figure 1. Hypothetical mechanism for the selective assimilation of bovine testicular fi-galactosidase by generalized gangliosidosis fibroblasts...

Figure 3. Effect of the concentration of ff-galactosidase in the medium on the rate of assimilation of ff-galactosidase by generalized gangliosidosis fibroblasts. The different symbols represent experiments performed at different times using the same enzyme preparation and fibroblast cell strain. The specific activity of the enzyme was approximately 4000 units/mg protein. One unit of enzyme is that amount which catalyzes the hydrolysis of 1 nmole p-nitrophenyl ff-galactopyrano-side per minute at pH 4.3 and 37° (18,).

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