Stimulation of cephalosporin production by methionine peptides in a mutant blocked in reverse transsulfuration.

The previously reported inability of methionine to stimulate cephalosporin C production in a cysteine auxotroph is due to cysteine interference with methionine uptake. In such a cse, "illicit transport" of alanylmethionine can be used to demonstrate the efficacy of methionine in such mutants blocked in the path from methionine to cysteine. This result supports the hypothesis that the stimulatory activity of methionine is not due to its ability to donate sulfur to the caphalosporin C molecule.