Substrate Dependent Reversibility of Inhibition by β‐Thujaplicin of Glucose and Acetate Respiration in Saccharomyces cerevisiae

Abstract

AbstractAttempts to determine the rate of uptake of β‐thujaplicin (TH) and its 1:1 rupric chelate (CuT+) in yeast cells showed in both cases a very rapid equilibration. In the concentration range where respiration is inhibited, most of the TH added was still present in the extracellular fluid, while CuT+ was almost completely removed.The inhibition of glucose respiration by TH was Completely removed when the cells were repeatedly washed, while inhibition of acetate respiration remained. Washing of CuT+ inhibited cells did not release the inhibition of either glucose or acetate respiration.The succinic acid dehydrogenase activity was the same in homogenates of both CuT+ and TH inhibited cells as in homogenates of non‐inhibited cells. Prior to homogenization acetate respiration was inhibited by 60 to 70 per cent by both inhibitors. Alcohol dehydrogenase activity was likewise not affected by TH and CuT+.The formation of acetyl coenzyme A was inhibited by both TH and CuT+ to about the same extent as the respiration of acetate.It is concluded that TH inhibits the acetate respiration by inhibiting the formation of acetyl coenzyme A from acetate. The same site of action is plausible also for CuT+ but in that case, additional sites of inhibition may also be located in the reactions in the Krebs cycle.