Tryptic activation of the insulin receptor. Proteolytic truncation of the alpha-subunit releases the beta-subunit from inhibitory control.

摘要: Trypsin exerts insulin-like effects in intact cells and on partially purified preparations of insulin receptors. To elucidate the mechanism these insulinomimetic effects, we compared structures insulin- trypsin-activated receptor species with their functions, including binding, autophosphorylation, tyrosine kinase activity. In vitro treatment wheat germ agglutinin-purified trypsin resulted proteolysis both alpha- beta-subunits. The activated form had an apparent molecular mass 110 kDa under nonreducing conditions, to 400-kDa receptor, was separated following reduction into 85-kDa beta-subunit related fragment a 25-kDa alpha-subunit fragment. Treatment whole prior isolation proteolytic modification only. this case, total 116 kDa, comprised 92-kDa again Values Km for peptide substrate phosphorylation Ki inhibition sites autophosphorylation within beta-subunits were similar receptors either by or trypsin. Insulin no additional effect rate truncated binding detected direct assay cross-linking bifunctional reagents. Based deduced amino acid sequence structural studies presented here concluded that from tryptic cleavage at dibasic site Arg576-Arg577. This accompanied loss separation alpha-beta heterodimers. As truncation results activation, it appears is constitutively function inhibit beta-subunit.