INTERMOLECULAR PHOSPHORYLATION BETWEEN INSULIN HOLORECEPTORS DOES NOTSTIMULATE SUBSTRATE KINASE-ACTIVITY

We photocoupled benzoylphenylalanine(B25), B29(epsilon)-biotin insulin (BBpa-insulin) to native insulin receptors to obtain a uniform recept or population with covalently bound, non-dissociable ligand. We employ ed BBpa-insulin-bound and autophosphorylated (activated) receptor to p hosphorylate substrate insulin receptor under conditions where the sub strate receptor never interacts with insulin. The substrate receptor b ecomes phosphorylated in this inter-receptor fashion and reaches a pho sphorylation state 50% of the maximal obtainable by autophosphorylatio n. However, this phosphorylation does not activate the substrate recep tor to any measurable degree. We conclude that intermolecular phosphor ylation of the insulin holoreceptors is unlikely to be of physiologica l significance.