Abstract
Yeast lacking Cu,Zn-superoxide dismutase (sod1Δ) exhibits methionine (Met) auxotrophy, primarily due to the depletion of NADPH required in the sulfur assimilation pathway by oxidative stress. In this study, we measured the ability of natural compounds, including ingredients in foods and dietary supplements, to restore the cell growth of sod1Δ in liquid and solid media without Met. Homocysteine at around 0.1 mM fully suppressed auxotrophy but in excess (> 0.4 mM) had a harmful effect. Methionine sulfoxide at concentrations from 0.05 to 0.8 mM and S-adenosylmethione (0.05 to 6.2 mM) completely relieved the growth defects caused by sod1Δ. Ascorbic acid (1 to 50 mM) restored sod1Δ growth, indicating that the action of this antioxidant could improve Met biosynthesis. However, ascorbic acid derivatives, ascorbic acid 2-glucoside and dehydroascorbic acid, did not show any activity. The suppressive effects of cysteine, N-acetylcysteine, and glutathione peaked at 0.1 mM, 0.5 mM, and 0.05 mM, respectively, but an excess of these agents was less effective. Suppression by dithiothreitol confirms that the thiol group is responsible for the amelioration of Met biosynthesis. No growth was restored for other categories of antioxidants including polyphenols, Trolox, melatonin, astaxanthin, and others.
