Title: Receptors for Lysosomal Enzymes and Glycoproteins
Abstract: Lysosomes are found in all eukaryotic cells, where they function principally in the disposal of macromolecules derived from uptake or from the turnover of cellular structures. Lysosomal enzymes catalyze hydrolytic reactions and operate invariably at acid pH. They are glycosylated enzymes. The glycosylation play a dual role: it serves as a protective role (glycosylated macromolecules are more resistant to denaturation), and second, it provides recognition signals required for the transport of both newly synthesized and preexisting lysosomal enzymes within and between cells. Studies on storage-disease cells and I-cell disease have provided support for the concept of receptor- mediated transfer of newly synthesized lysosomal hydrolases to lysosomes via recognition signals attached to the enzymes. These recognition signals are carbohydrate in nature. There are at least two recognition signals (and, correspondingly, two cellular receptors) found on lysosomal enzymes which mediate transfer to lysosomes: (1) mannose 6-phosphate-terminated oligosaccharides and (2) mannose-terminated oligosaccharides. Very little is known about the intracellular movement, but intracellular mannose 6-phosphate-specific receptors are found. Most of the receptors are found within cells, with only a small fraction on the cell surface. Most plasma glycoproteins have complex oligosaccharides terminated in sialic acid. The presence of sialic acid as the terminal sugar on the oligosaccharide chain protects plasma glycoproteins from being recognized in vivo.
Publication Year: 1983
Publication Date: 1983-01-01
Language: en
Type: book-chapter
Indexed In: ['crossref']
Access and Citation
Cited By Count: 20
AI Researcher Chatbot
Get quick answers to your questions about the article from our AI researcher chatbot