Oxygen consumption and carbon dioxide evolution during the cell cycle of Schizosaccharomyces pombe

• Main Author: Creanor, James
• Published: University of Edinburgh 1976
• Subjects: 571.29
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.645130

Oxygen uptake and CO2 evolution were measured in synchronous cultures of the fission yeast Schizosaccharomyces pombe, growing in a minimal medium. The rate of oxygen uptake increased abruptly at the middle of the cycle and again at the end of the cycle. During the intervening periods the rate remained constant. Oxygen uptake was measured nanometrically and polarographically. The rate of CO2 evolution doubled sharply at the tin of nuclear division (0.75 of the way through the cycle). For the remainder of the cell cycle, the rate remained constant. Similar step wise increases in the rate of CO2 evolution could be induced by adding glucose to late exponential cultures. So various attempts were made to show that the steps in the rate of CO2 evolution in synchronous cultures were not artefacts induced by the synchronisation technique. The addition of DNA synthesis inhibitors and a nuclear division inhibitor to synchronous cultures had no effect on the patterns of oxygen uptake and CO2 evolution. Similarly in an induced synchronous culture, in which DNA synthesis, nuclear division and cell division - but not "growth" - were synchronised, oxygen uptake and CO2 evolution showed a continuous increase and not a "synchronous" pattern. Evolution of 14'CO2 was measured in synchronous cultures. Various technical problems made the interpretation of these results difficult but there is a similarity between the measurement of 14CO2 evolution and CO2 evolution measured nanometrically in synchronous cultures. Experiments with protein and RNA synthesis inhibitors suggested either that an increase in oxygen uptake and CO2 evolution was dependent on continued protein and RNA synthesis; or that in the absence of either protein or RNA synthesis, the demand for energy decreased and hence the flux through the energy yielding pathways which result in oxygen uptake and CO2 evolution also decreased. Other experiments showed that optical density increase doubled in asynchronous culture at about the same time that CO2 evolution doubled in rate. Both hexokinase and ATP were shown to increase exponentially in synchronous cultures and are therefore not obvious regulators of, or obviously regulated by, oxygen uptake or CO2 evolution. The control of respiratory and fermentative activity is discussed and it is suggested that the levels of intermediates in the E pathway and the TCA cycle control the activities of these pathways.