Abstract
Under special conditions dried yeast preparations can be obtained which show a typical Pasteur effect with a normal quotient (MQ). mol CO 2 fermentation suppressed by oxidation mol O 2 consumed of 1 to 2.5. Quickly dried bakers' yeast without further treatment was used in the first place. The Pasteur effect is strictly reversible. Moreover, it is nearly completely inhibited by para-nitrophenol (1·10 −3 M) and less completely by 2,4-dinitrophenol and 3,5-dinitro- o-cresol. While almost no phosphate is esterified anaerobically, some phosphorylation occurs in oxygen, and this latter phosphorylation is then completely inhibited by para-nitrophenol. Because such a dried bakers' yeast still contains 50% cells able to grow, the yeast was treated with ultrasonic vibration for 60 to 80 mins. Although this destroys some ATP-ase, the fermentation is still fairly constant for 60 to 80 min in the presence of low concentrations of phosphate. All observations can be repeated with the vibrated yeast with the same results. This yeast is now permeable to cofactors (cozymase, ATP, etc.) and the fermentation rate is tripled by addition of optimal concentrations of these factors. Another yeast type, Spiegelman's yeast K, gives the same results without ultrasonic treatment. It contains only 2% of living cells. It shows a specific activation by cozymase which has been treated for some minutes with carbonate (ph 10.5). This activation is weaker in oxygen. This leads to a real or apparent increase of the MQ up to 4.
Published Version
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