Covalent glycoinositolphospholipid (GPI) binding to hemoglobin is associated with insulin-activation of erythrocyte membrane protease

Abstract

Recently, it was demonstrated that prolonged hyperinsulinism associated with hypoglycemia, both in vivo and in vitro, caused covalent glycoinositolpho- spholipid (GPI) binding to the C termini of both hemoglobin -chains, which re- sulted in the formation of a novel, hitherto unrecognized, minor hemoglobin fraction (GPI-Hb) (Niketi}et al., Biochem. Biophys. Res. Commun.239 (1997) 435). In this study it was demonstrated that exposure of erythrocyte membranes to insulin causes the activation of membrane protease as well as that the formation of GPI-Hb paral- lels its activity. It is suggested that the insulin-activated protease is able to catalyze, albeit slowly, the transpeptidation, i.e., the replacement of the carboxy-terminal amino acid(s) residues of the Hb-chains with GPI as an exogenous nucleophile. To our knowledge the present results show for the first time that insulin stimulates pro- tease activity in erythrocyte membranes, as well as that insulin-activated protease may be involved in post-translational GPI binding to proteins.