Lactate dehydrogenase: Lactate oxidation and role of ROS

Abstract

Lactate dehydrogenase is a well-studied nonspecific biomarker with profound implications in diseases like cancer.
In vitro investigations into the mechanism of lactate dehydrogenase action described herein are based on our group’s earlier reported thermodynamic calculations. While the reverse (pyruvate to lactate) reaction is thermodynamically favourable, the forward (lactate to pyruvate) reaction is unfavourable at physiological conditions. NADH consumption (lactate formation) rates were high, in the range of 2000-3000 M^-1 s^-1 contrary to the NADH formation (pyruvate formation) rates that were low (50 to < 300 M^-1 s^-1) under classical reaction conditions. Interestingly, the lactate to pyruvate reactions driven with ROS (peroxide, hydroxyl radical or superoxide) alone demonstrated strikingly high reaction rates (~ 700-2500 M^-1 s^-1). However, inclusion of lactate dehydrogenase into such reactions rapidly lowered the NADH formation rates. GC-MS and FT-IR results supported the superoxide-assisted oxidation of lactate to pyruvate in KO₂ containing reaction mixtures. DFT analysis further demonstrated the strong thermodynamic viability of ROS mediated oxidation of lactate. Comprehensively, the findings suggest an alternate route of lactate oxidation, i.e., ROS mediated catalysis of lactate to pyruvate. The findings support the murburn concept because the observed ROS-dependent lactate oxidation is consistent with a central prediction of the murburn framework.