ACETYLCHOLINESTERASE ACTIVITY OF NORMAL AND DIABETIC HUMAN ERYTHROCYTE-MEMBRANES - THE EFFECT OF OXIDATIVE AGENTS

The activity characteristics of membrane acetylcholinesterase from red blood cells of diabetic patients are very different from those of hea lthy donors: the limiting enzyme reaction rate is 17.2 +/- 0.8 mu mol acetylthiocholine per ml packed cells per min compared with 13.1 +/- 0 .8 mu mol for control cells. The Michaelis constants for substrate are the same: 0.061 +/- 0.007 mM for diabetic and 0.061 +/- 0.004 mM for control cells. Cell exposure to oxidative agent (t-butyl hydroperoxide ) significantly changes the enzyme activity parameters. The limiting e nzyme reaction rate increases but the affinity for the substrate decre ases at lower oxidant concentrations (up to 0.1 mM for the ''diabetic' ' erythrocytes and up to 0.4 mM for the control ones). At higher oxida nt concentrations both the limiting reaction rate and the Michaelis co nstant decrease. The susceptibility of erythrocyte membranes of diabet ic patients to oxidative stress is much higher in comparison with cont rol erythrocyte membranes.