Biological potency of covalently linked insulin-receptor in rat adipocytes: Comparison with the potency of reversible complexes

Abstract

Irradiation of photoreactive insulin derivatives in the presence of isolated rat adipocytes produces a prolonged stimulation of lipogenesis in the cells even after exogenous and reversibly bound derivative has been removed by extensive washing. The quantitative nature of this response has now been studied using 125I-B2(2-nitro-4-azidophenylacetyl)des-Phe B1-insulin. This derivative possesses nearly full biological potency and binding affinity prior to irradiation. After covalent linkage to adipocytes the efficacy of the derivative is reduced to 25 ± 4% of the reversibly bound derivative, viz. 4-times as much needs to be covalently associated as reversibly bound to induce the same level of stimulation of lipogenesis. This reduced relative molar potency is due to a reduced ability of specific covalent insulin-receptor complexes to trigger a response.