FIG. 8.

Schematic drawing of the hypothetical metabolic routes (glycolysis, Krebs, and glyoxylate cycles), modified from Tabak et al. (46), involved in succinate accumulation in the Klsdh1Δ mutant. The major sources of NAD(P)H production during growth on glucose and lactate are indicated. The pentose phosphate shunt has been included because in K. lactis this pathway is probably constitutively operative. The NADPH produced in this pathway can be reoxidized directly via mitochondrial membrane dehydrogenase; ACS, PDC, MLS, and ICL indicate the genes coding for the following activities, respectively: acetyl-coA synthetase, pyruvate decarboxylase, malate synthase, and isocitrate lyase. LDH indicates the mitochondrial activities responsible for lactate oxidation encoded by the KlCYB2 and KlDLD1 genes. PDH, pyruvate dehydrogenase complex. To indicate the block in the SDH route, SDH has been crossed out (×).