TYROSINE IS INVOLVED IN PROTECTION FROM OXIDATIVE STRESS IN SACCHAROMYCES-CEREVISIAE

The phenotypic characterization of a Saccharomyces cerevisiae mutant u nable to grow under agitated conditions is presented here. When this s train was incubated under aerobic conditions, it did not grow and the viability of the culture decreased. The loss in viability was prevente d by the addition of antioxidants or chelating agents to the medium, i ndicating that this mutant was unable to withstand the oxidative stres s generated by aerobic metabolism. This strain was complemented with p lasmids from a yeast genomic library. The transformants that were obta ined carried plasmids harbouring the TYR1 gene, which codes for one of the enzymes involved in tyrosine biosynthesis. A monogenic S. cerevis iae tyr1 mutant obtained from the Yeast Genetic Stock Center showed hi gher sensitivity to hydrogen peroxide than a TYR1 strain. This sensiti vity was reverted when this strain was complemented with the TYR1 gene . Considering these results, we propose that tyrosine plays a role in the protection against oxidative stress.