Analysis of the kinetic characteristics of lactate dehydrogenase from the rat brain during ischemia and reperfusion

We studied the activity and kinetic characteristics of lactate dehydrogenase (LDH) during partial global ischemia and reperfusion of rat brain. We found that occlusion of carotid arteries for 1 hour results in an increase in the LDH activity within the entire range of pyruvate concentrations that we used in our study. The character of the concentration dependence of the enzyme activity did not change and Ki for the area of inhibition by pyruvate excess did not significantly increase. The increase in the efficacy of LDH catalysis during ischemia is determined by an increase in Vmax associated with an insignificant decrease in Km. During postischemic brain reperfusion, LDH activity at all studied pyruvate concentrations decreased. The optimum point on the plot of concentration dependence shifts to the area of higher pyruvate concentrations, which is related to a decrease in Ki. A dramatic decrease in the efficacy of catalysis is determined by a considerable increase in Km and a decrease in Vmax. Possible mechanisms of changes in the activity and kinetic characteristics of LDH during ischemia and reperfusion of the brain are discussed.