Oxalate production from glyoxylate by lactate dehydrogenase in vitro: inhibition by reduced glutathione, cysteine, cysteamine.

Lactate dehydrogenase is known to act as a dismutase converting glyoxylate to oxalate and glycolate. LDH (sources: human erythrocytes, human plasma; rabbit muscle; rat liver) activity was assayed at 340 nm using glyoxylate (5.0 mmol/l) and NADH. The LDH activity (approx. % of control) in all the cases decreased respectively in the presence of 5.0 and 10.0 mmol/l of cysteine (45 and 20), cysteamine (45 and 20), and GSH (55 and 30). This decrease in LDH activity resulted in decreased oxalate production from glyoxylate (0.5 mmol/l). A 50% inhibition in oxalate production was observed in presence of 0.3 mmol/l cysteine, 0.35 mmol/l cysteamine, and 2.0 mmol/l GSH. The results suggest that the net LDH activity towards oxalate production may be regulated by the free SH-groups in the cell. This possibility needs evaluation as a tool to lower endogenous oxalate production and the associated risk of stone formation.