Vanadate stimulated NADH oxidation in sarcoplasmic reticulum membrane.

Vanadate stimulated NADH oxidation was detected in sarcoplasmic reticulum membrane preparations. The reaction showed enzymatic character, with half maximal activating concentration of 1.2 mM vanadate and maximal NADH oxidation 50 nmol/mg protein/minute. Acidic pH, micromolar free Ca2+ concentration and decavanadate addition increased the rate of NADH oxidation. The described enzyme activity is similar to the ones observed in erythrocyte liver and cardiac plasma membranes. The vanadate stimulated NADH oxidation in sarcoplasmic reticulum preparations does not seem to originate from other contaminating membrane elements. The presence of this enzyme activity in the sarcoplasmic reticulum should be taken into consideration when planning experiments with vanadate, especially when measuring ATPase activity through NADH oxidation with coupled enzymatic assay.