Synthesis of superoxide dismutase, catalase and other enzymes and oxygen and superoxide toxicity during changes in oxygen concentration in cultures of brewing yeast

Abstract

The physiological effects on brewing yeast, growing in semi‐defined wort medium, of a sudden transition from aerobiosis to anaerobiosis were studied. Two yeast strains were examined, used for ale and lager fermentations respectively. The reverse transition (from anaerobiosis to aerobiosis) was also examined. Transitions were applied by changing the sparging gas during growth or in stationary phase, and the effects on the specific activities of certain key enzymes and on the viability of the cultures were examined. Neither type of transition led to significant changes in growth rate, the rate of ethanol production or the specific activities of alcohol dehydrogenase and pyruvate decarboxylase. The most significant change was in the specific activity of CuZn‐superoxide dismutase, which showed a rapid increase in activity on transition from anaerobiosis to aerobiosis, and a decrease in activity on the reverse transition. Catalase activity in the ale yeast generally followed that of CuZn‐superoxide dismutase, whereas in the lager yeast it remained unchanged by the transitions. The transition from anaerobiosis to aerobiosis caused increases in citrate synthase and Mn‐superoxide dismutase, though only after a significant lag period. Aerobic to anaerobic transitions caused a decrease in Mn‐superoxide dismutase activity, while citrate synthase remained unchanged. Anaerobically grown cells showed a rapid loss in viability on exposure to oxygen (5–7% in the first hour), while aerobically grown cells were unaffected. When anaerobically grown cells were exposed to 0·25 mM‐potassium superoxide, there was an 8% loss of viability within 10 min, whereas aerobic cells were not affected. It is concluded that the toxic effect of oxygen is due to superoxide (or a species derived from it) and that the CuZn‐superoxide dismutase (but not the Mn‐isoenzyme) plays a role in protecting the cells. The de novo synthesis of the CuZn‐enzyme is not always rapid enough to confer full protection.

Air pressure effects on biomass yield of two different Kluyveromyces strains

“…Among these factors are the catabolic repression [9], nutrient limitation [19], heat shock [10], even respiratory adaptation, that can be considered as a stress response [20,21]. Cells have other defensive mechanisms than those studied in this work that protect the cells from oxygen radicals, such as several peroxidases and nonenzymatic species [6].…”

Role of the non‐respiratory pathways in the utilization of molecular oxygen by Saccharomyces cerevisiae

“…103 Hence, it has been postulated that Cyc7p plays a protective role during oxidative stress, because it may behave as an electron sink for the partially assembled complex III under conditions of low defence against ROS. 29,36,105,160 However, because of the numerous constraints of Cyc7p detection, there is no conclusive evidence that functional Cyc7p is present in anaerobic cells.…”

“…catalase, superoxide dismutase, glutathione peroxidase) that are present in anaerobic cells. 36,147 Indeed, the basal level of such enzymes in anaerobic cells may minimize the oxidative damage caused by CNR systems upon oxygenation. Moreover, the relative level of CPR1, NADH-b5 reductase and cytochrome b5, as well as interactions between these redox partners, may strongly influence the extent of electron leakage, e.g.…”

The Combined Effects of Oxygen Supply Strategy, Inoculum Size and Temperature Profile on Very-High-Gravity Beer Fermentation by Saccharomyces cerevisiae

“…16,31,39,46,48,49,67 Conversely, delivering too much oxygen has been reported to contribute to yeast degeneration. 12 The amount of oxygen required by a specific yeast strain is dependant on several factors including the physiological condition of the cells, the inoculation rate, and fermentation conditions. 37,39,46 In addition to the level of oxygen provided, several researchers have established that the timing of supply is critical.…”