The existence in Saccharomyces cerevisiae of a protective mechanism in response to methylglyoxal: the role of D.lactate movement across the inner mitochondrial membrane and its function on gluconeogenesis

Methylglyoxal (MG), an intrinsic intermediate of glycolysis, is an extremely toxic compound, able to react with, and modify, different molecular targets. In yeast a established pathway for MG detoxification by the action of the glyoxalase system converts, in the cytosol, MG into D-Lactate in the presence of glutathione (Aguilera et al; 2004). Previous studies have already reported that isolated Saccharomyces cerevisiae mitochondria (SCM) can take up and oxidise D-lactate externally added to them and shown the existence of two carriers for D-lactate mitochondrial metabolism: D-lactate/H+ symporter and D-lactate/pyruvate antiporter (see Pallotta et al; 2004). Moreover, the role of the two mitochondrial enzymes (Dld1p and Dld2p) that accomplish D-lactate oxidation was studied. Here, a novel aspect the occurrence of a D-lactate/L-malate antiporter activity is highlighted. This activity differs from that of the D-lactate/pyruvate carrier in (a) kinetics (Km and Vmax values are about 20 μM and 5.8 nmol min(-1) mg protein(-1) and 30 μM and 400 nmol min(-1) mg protein(-1), respectively), (b) sensitivity to inhibitors, (c) for the inhibitor α-CCN- which inhibits in a competitive manner the pyruvate appearance (Ki about 0.1 mM) and in a non-competitive manner the malate appearance (Ki about 0.3 mM) outside SCM and, finally (d) pH profiles. D-lactate translocators, Dld1p and Dld2p could account for the removal of the toxic methylglyoxal as well as to supply pyruvate and malate, in the cytosol, for gluconeogenesis. References Aguilera J. Prieto JA. 2004. Yeast cells display a regulatory mechanism in response to methylglyoxal. FEMS Yeast Res. 4(6):633-41. Pallotta ML, Valenti D, Iacovino M, Passarella S. 2004. Two separate pathways for d-lactate oxidation by Saccharomyces cerevisiae mitochondria which differ in energy production and carrier involvement. BBA-Bioenergetics 1608:104-13. PDF created