Glutathione formation in Penicillium chrysogenum: stimulatory effect of ammonium

Penicillium chrysogenum produced glutathione after growth in a defined medium containing 10 mM-NH4Cl as the sole source of nitrogen. The use of higher ammonium concentrations (100 mM) resulted in stimulation of growth and glutathione formation. In addition, increases in the intracellular pools of glutamate, alanine and glutamine, proportional to the amount of ammonium present in the medium were observed. Resting cell systems, prepared from cells previously grown with ammonium, were able to produce glutathione when incubated with ammonium or the amino acids glutamate, alanine and glutamine. A mutant lacking NADP-dependent glutamate dehydrogenase activity (which has a leaky phenotype on ammonium as sole nitrogen source) required glutamate to synthesize glutathione. Resting cell systems of this mutant, prepared from cells previously grown with ammonium, did not produce glutathione even when incubated with glutamate or glutamine. On the other hand, resting cell systems of this mutant produced glutathione if prepared from cells previously grown with glutamate. The addition of glutamate to resting cell systems of the wild-type strain stimulated the synthesis of gamma-glutamylcysteine synthetase, the first enzyme of glutathione biosynthesis.