The intensity of
free radical processes and the regulation of
NADP-isocitrate dehydrogenase (EC 1.1.1.42;
NADP-IDH) activity have been studied in the cytoplasmic fraction of normal and ischemized rat myocardium. Chemiluminescence parameters, such as the light sum (S) of slow flash and the tangent of the kinetic curve slope angle (tanalpha1), which characterize the intensity of
free radical processes, were increased in
ischemia 2.1- and 20.0-fold, respectively. The slow flash intensity (Imax) was increased 22-fold. The contents of lipid peroxidation products--diene conjugates and malonic dialdehyde--were increased 11.9- and 4.7-fold, respectively, suggesting pronounced oxidative stress. Using homogenous
enzyme preparations of
NADP-IDH isolated from the normal and experimentally ischemized rat myocardium, a number of catalytic properties of the
enzyme were characterized for normal and pathologic conditions.
NADP-IDH from the normal and ischemized myocardium had the same electrophoretic mobility and was regulated similarly by Fe2+, Cu2+, Zn2+, and also with
succinate and
fumarate. However, under normal and pathologic conditions
NADP-IDH was different in the affinity for substrates and in the sensitivity to inhibitory effects of
hydrogen peroxide,
reduced glutathione, and of Ca2+. The degree of synergy in the
enzyme inhibition with Fe2+ and H2O2 was less pronounced in
ischemia. The inhibitory effect of the reaction product
2-oxoglutarate was higher under normal conditions than in
ischemia (the Ki values were 0.22 and 0.75 mM, respectively). The specific features of the
NADP-IDH regulation in
ischemia are suggested to promote the stimulation of the
enzyme functioning during increased level of
free radical processes, and this seems to be important for
NADPH supplying for the
glutathione reductase/
glutathione peroxidase antioxidant system of cardiomyocytes.