ABSTRACT
The functional significance of the carbohydrate is unknown however, removal of both sialic acid and galactose by exoglycosidases results in a decrease in insulin binding. The insulin receptor is synthesized as a single precursor which is post translationally modified by proteolysis into two distinct subunits. In the intact cell, insulin-binding subunit is sensitive to proteolytic cleavage, suggesting that it has a major extracellular domain The β subunit of the insulin receptor has a mol wt of 95,000 and, in contrast to the α subunit, appears to be a transmembrane protein. In addition, the β subunit of the insulin receptor is an insulin-sensitive protein kinase, suggesting that it contains the effector function of the insulin receptor. The substrate hypothesis has gained support recently by the discovery of a 185,000- dalton protein designated pp185 which undergoes tyrosine phosphorylation during insulin binding.
