Monocarboxylate such as lactate and pyruvate play an important role in cellular metabolism. Lactic acid is produced as the end product of glycolysis. Some tissues, such as white skeletal muscle and, red blood cells, use this pathway to generate most of their ATP under normal physiological conditions. All tissues become dependent on this pathway during abnormal conditions such as hypoxia and ischaemia. Lactic acid, produced during normal glycolysis, must be transported out of cells to sustain maintain high rate of glycolysis. Failure to export lactic acid leads to accumulation of cellular lactic acid followed by an increase in pH and inhibition of glycolysis. Some tissues, such as brain, heart, and red skeletal muscle, readily oxidize lactic acid, and must import lactic acid into the cells. Lactic acid transport is mediated by a group of proton-linked membrane transporters called monocarboxylic acid transporters (MCTs). At least 9 MCT-related proteins (MCT1-9) have been identified in mammals that are expressed in a tissue specific manner. MCT2/MOT2 (mouse 484aa, rat 489aa, human 478aa, chromosome 12q13) is less widely distributed than MCT. It is associated with tissues that demonstrate a high uptake affinity for lactate and pyruvate such as the kidney and liver (for gluconeogenesis) and neurons (for oxidation). It may function in transporting lactate from intestine and erythrocytes. MCT1 is most closely related to MCT1 (~55% identity, whereas homolog with other MCT1-MCT8 isoforms is less (~35-53%). Both N and C-termini are predicted to be cytoplasmic.