Summary: Activities of glycolytic enzymes were determined in elutriation fractionated cultures of grown on different carbon sources. Almost pure fractions of single cells at the G1 stage of cell division were obtained for some of the growth conditions tested, whereas other stages were enriched in particular fractions. Specific activities of glucose-6-phosphate dehydrogenase and alcohol dehydrogenase were found to be constant during the cell cycle, as reported by van Doorn (1988), 170, 4808–4815, and (1988), 134, 785–790. In contrast to the earlier reports, the activities of hexokinase, phosphofructokinase, pyruvate kinase and trehalase were also constant in different stages of the cell cycle. For hexokinase and phosphofructokinase it was shown that the apparent specific activity in a cell-free extract strongly diminished when extracts contained less than 0·5-1 mg protein ml. In the experiments of van Doorn (1988) the protein content of the outer fractions was up to 20 times lower than that of the central fractions, suggesting an alternative explanation for the observed changes in enzyme activities during the cell cycle. Therefore, we want to rectify the observations presented by van Doorn (1988), and conclude that the activities of the glycolytic enzymes do not vary greatly during the cell cycle of .


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