Fig 9.

Pyruvate overflow pathway through branched-chain amino acid metabolism. The metabolism of carbohydrates leads to the generation of pyruvate, which results in the generation of lactic acid, the major acidic end product responsible for tooth demineralization and caries formation. Pyruvate can be rerouted to the synthesis of branched-chain amino acids by the action of the ilv biosynthetic pathway. CcpA aids in the activation of ilv when cells are exposed to an acidic environment. Branched-chain amino acids, in turn, are important molecules for genetic regulation via their role as coeffectors for CodY transcriptional regulation. As branched-chain amino acid synthesis increases, CodY-dependent repression of the ilv genes also increases, resulting in repression of these gene transcripts when bcAAs are in excess.