[Interaction of the lactate dehydrogenase-NAD pyruvate complex with lung sarcoplasmic reticulum membranes].

Lactate dehydrogenase (LDH) from pig skeletal muscle can catalyse the reaction of covalent bond formation between pyruvate and NAD+. This process leads to the loss of the enzyme activity, since the abortive complex formed cannot dissociate under the reaction conditions. The formation of the LDH.NAD-pyruvate complex (LDH-adduct) can be followed both by measuring the adduct absorbance and the fluorescence of toluidinylnaphthalene sulfonate bond to LDH. The enzyme activity is recovered when light sarcoplasmic reticulum membranes are added to the abortive complex. The complete recovery takes about two hours at room temperature. After this the enzyme activity becomes equal to that measured in the samples which initially contained the native enzyme or in the samples contained LDH.NAD-pyruvate in different stoichiometries. The process of LDH activity recovery is a result of dissociation of the LDH-adduct complex in the presence of sarcoplasmic membranes. A di-cyclic derivative of the adduct was isolated by gel filtration and identified spectrophotometrically. Interaction of the inactive LDH.NAD-pyruvate complex with sarcoplasmic reticulum membranes may be a mechanism providing recovery of the enzyme activity in the cell.