The conversion of leucine to alpha-ketoisocaproic acid and its metabolic consequences for Escherichia coli K12.

The amino acid L-leucine serves as a good auxiliary nitrogen source for Escherichia coli K12, and in so doing is converted to alpha-ketoisocaproic acid which is excreted into the medium. L-Leucine does not serve as sole nitrogen source. Cells incubated with L-leucine as sole nitrogen source do not grow, although they do metabolize leucine, and accumulate ketoisocaproic acid in the medium. Where glycine is the only other nitrogen source, the presence of L-leucine greatly increases the growth rate even at concentrations so low that its contribution as nitrogen donor is unlikely to be important.