Genetics and Regulation of the Major Enzymes of Alanine Synthesis inEscherichia coli

Genetic analysis of alanine synthesis in the model genetic organism Escherichia coli has implicated avtA, the still uncharacterized alaA and alaB genes, and probably other genes. We identified alaA as yfbQ. We then transferred mutations in several transaminase genes into a yfbQ mutant and isolated a mutant that required alanine for optimal growth. For cells grown with carbon sources other than pyruvate, the major alanine-synthesizing transaminases are AvtA, YfbQ (AlaA), and YfdZ (which we designate AlaC). Growth with pyruvate as the carbon source and multicopy suppression suggest that several other transaminases can contribute to alanine synthesis. Expression studies showed that alanine modestly repressed avtA and yfbQ but had no effect on yfdZ. The leucine-responsive regulatory protein (Lrp) mediated control by alanine. We purified YfbQ and YfdZ and showed that both are dimers with K(m)s for pyruvate within the intracellular range of pyruvate concentration.