Although GSH is wildly distributed in the nature, the
extraction of this tripeptide from yeast cells seems to be
the only commercial available biotechnological production
method to date. From the viewpoint of achieving an
economical process, the higher the intracellular GSH
content, the more products could be obtained supposing
the biomass concentration keeps constant. Therefore,
most industrial microbiologists put emphases on how to
increase, as much as possible, the intracellular GSH
content of yeast. However, in a normal yeast strain, the
intracellular GSH content always remains at a stable
level, since g-glutamylcysteine synthase, the first enzyme
in GSH biosynthesis, is feedback regulated by GSH [14].
Although this regulation process could be released by
chemical mutation, excessive intracellular GSH would
alter the normal intracellular redox state [15]. If
excessive GSH could be excreted extracellularly, and