FEMS MicrobiologyLetters 42 (1987) 27-31 27 Published by Elsevier FEM 02764 The Pasteur effect in yeasts: mass spectrometric monitoring of oxygen uptake, and carbon dioxide and ethanol production D. Lloyd and C.J. James Department of Microbiology, University College, Newport Road, Cardiff U.I( Received and accepted 9 January 1987 Key words: Saccharomyces eerevisiae," Saccharomyces uvarum; Pasteur effect; Glycolysis; Fermentation; (Mass spectrometry) 1. SUMMARY 2. INTRODUCTION Simultaneous and continuous monitoring of dissolved 02, CO 2 and ethanol in suspensions of Saccharomyces uvarum and Saccharomyces cere- visiae, by means of a quadrupole mass spectrome- ter fitted with a silicone rubber membrane inlet, enabled a study of 0 2 inhibition of glycolysis (Pasteur effect). Calculation of Pasteur quotients (ratios of anaerobic to aerobic glycolytic rates) give similar values when corrected both for re- spiratory CO 2 production and ethanol oxidation under aerobic conditions. For S. cerevisiae the apparent K m for 0 2 of the respiration of catabo- lite derepressed cells was 1 /~M and the apparent K i values for O 2 as an inhibitor of glycolysis were 12.7 and 7/~M, respectively, when measurements were made on CO 2 evolution and ethanol produc- tion. Correspondence to: D. Lloyd, Dept. of Microbiology, Univer- sity College, Newport Rd., Cardiff, CF2 1TA, Wales, U.K. The inhibition of glycolysis by 0 2 has been extensively studied in a wide variety of organisms and tissues [1], but the exact nature of the control mechanisms involved is still debated [2,3]. This Pasteur effect, originally discovered in yeast [4] is easily investigated in that organism which shows rapid and pronounced responses to changes in sugar or 0 2 concentrations [5,6]. S. cerevisiae has the added advantage that many mutant strains defective in different enzymes of glycolysis have been isolated [7]. Despite these advances, and the identification of several key control points, e.g., hexose transport [8], phosphofructokinase [9,10], pyruvate/kinase [11], and NAD+-dependent iso- citrate dehydrogenase [12], many aspects of the Pasteur effect remain unexplained. We report here a technique that greatly facilitates research on the Pasteur effect, a continuous and simultaneous mass spectrometric monitoring of 0 2, CO 2 and ethanol dissolved in yeast suspensions. When performed under carefully controlled conditions of gas ex- change [13], rate measurements on all 3 compo- nents may be determined under aerobic or anaerobic conditions, or at very low 0 2 concentra- 0378-1097/87/$03.50 © 1987 Federation of European Microbiological Societies