[Study of spin-labeled microsomal membrane proteins by their reaction with ascorbic acid]

Kinetics of the reduction of nitroxyl radicals bound to SH-groups of microsome membrane proteins by ascorbic acid was investigated. The reduction involves two steps. During the first quick step mainly the radicals with weak immobilization located on the membrane surface are reduced. At the second slow step more immobilized radicals located in hydrophobic membrane regions take part in the reaction. A kinetic analysis of the process showed that the slow step is not determined by the slow movement of protein or its fragments, for instance, from the membrane depth to its surface, and apparently is conditioned by lower ascorbic acid concentration in the membranes.