Effects of the Fenton reagent on transport in yeast

In the facultatively anaerobic yeast Saccharomyces cerevisiae the uptake ra te and the accumulation ratio of 2-aminoisobutyric acid was decreased by so me 30 % by Fenton's reagent (FR), a powerful source of OH radicals. Likewis e, the uptake of glutamic acid, leucine and arginine was diminished. The me diated diffusion of 6-deoxy-D-glucose was not affected. The H+ symport of m altose and trehalose was inhibited by some 40 % both in the initial rate an d in the accumulation ratio. FR had a dramatic inhibitory effect when prese nt during preincubation with 50 mmol/L glucose. In the obligately aerobic L odderomyces elongisporus the uptake of all amino acids tested was decreased by 15-30 %, that of 6-deoxy-D-glucose by about 10 %. The initial rates of uptake of maltose and trehalose were depressed by FR by 40 % and the accele ration of uptake observed after 8 min of incubation, was abolished by FR co mpletely. Acidification rate of the external medium by S. cerevisiae in the presence of glucose or galactose was enhanced three-fold, that after subse quently added K+ was substantially decreased. FR appears to have a dual eff ect on sugar and amino acid transport processes in yeast: (1) it blocks car rier protein synthesis, (2) it inhibits the source of energy for transport. It does not appreciably affect the carrier proteins themselves.