Abstract

Autonomous ultradian metabolic oscillation (T~=50 min) was detected in an aerobic chemostat culture of Saccharomyces cerevisiae. A pulse injection of GSH (a reduced form of glutathione) into the culture induced a perturbation in metabolic oscillation, with respiratory inhibition caused by H_2S burst production. As the production of H_2S in the culture was controlled by different amino acids, we attempted to characterize the effects of GSH on amino acid metabolism, particularly with regard to branched chain and sulfur-containing amino acids. During stable metabolic oscillation, concentrations of intracellular glutamate, aspartate, threonine, valine, leucine, isoleucine, and cysteine were observed to oscillate with the same periods of dissolved O_2 oscillation, although the oscillation amplitudes and maximal phases were shown to differ. The methionine concentration was stably maintained at 0.05 mM. When GSH (100 uM) was injected into the culture, cellular levels of branched chain amino acids increased dramatically with continuous H_2S production, whereas the cysteine and methionine concentrations were noticeably reduced. These results indicate that GSH-dependent perturbation occurs as the result of the promotion of branched chain amino acid synthesis and an attenuation of cysteine and methionine synthesis, both of which activate the generation of H_2S. In a low sulfate medium containing 2.5 mM sulfate, the GSH injections did not result in perturbations of dissolved O_2, NAD(P)H redox oscillations without burst H_2S production. This suggests that GSH-dependent perturbation is intimately linked with the metabolism of branched-chain amino acids and H_2S generation, rather than with direct GSH-GSSG redox control.

• Keywords: cellular amino acid concentrations; hydrogen sulfide; GSH dependent respiratory inhibition; Saccharomyces cerevisiae; ultradian metabolic oscillation