Lysosomal release defect

Lysosomal enzymes are glycosylated and modified in a characteristic way. Most importantly, when they arrive in the Golgi apparatus, specific mannose residues in their oligosaccharide chains are phosphorylated. This phosphorylation is the critical event that removes them Corn the secretion pathway and directs them to lysosomes. Genetic defects affecting this phosphorylation produce I-ceU disease in which lysosomal enzymes are released into the ejctracellular space, and inclusion bodies accumulate in the cell, compromising its function. 

Mendla, K. Baumkotter, J. Rosenau, C. Ulrich-Bott, B. Cantz, M. Defective Lysosomal Release of Glycoprotein-Derived Sialic Acid in Fibroblasts from Patients with Sialic Acid Storage Disease. Biochem. J. 1988, 250, 261-267. 

TCII plays a major role in transport of cobalamins to tissues. A receptor for the TCII-B12 complex has been tentatively identified in vitro on HeLa cells,Ehrlich ascites cells,and human fibroblasts. The bound complex is transferred into the cell, where the cobalamin is released and the TCII is degraded in lysosomes (Figure 38-18). An inborn error of vitamin Bj2 metabolism has been attributed to a defect in vitamin B12 release from lysosomes. A congenital... 

Another possible defect would be failure to esterify retinol by the RPE. Reading (1966) suggested that this could lead to an accumulation of free retinol which might cause breakdown of lysosomes and release of their potentially damaging contents. Although there has been some support for this view in studies on the... 

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