Figure 2.

Visualization of the valine degradation pathway and the interaction with LDH. Abbreviations of enzyme names are shown in boldface BCAT: branched-chain aminotransferase; BCKDH: branched-chain alpha-keto acid dehydrogenase; LDH: lactate dehydrogenase. LDH can convert 3-methyl-2-oxobutanoate, which is the product of valine after transamination, into alpha-hydroxyisovalerate to balance the redox potential under hypoxic conditions. Under aerobic conditions, 3-methyl-2-oxobutanoate can be further degraded by the enzymes of branched-chain amino acid catabolism. In contrast, alpha-hydroxyisovalerate cannot be metabolized any further and is excreted in urine.