This study examined how ammonium ions (NH4+) affect glycolysis and respiration in three yeast species: Saccharomyces uvarum, Schizosaccharomyces pombe, and Candida utilis. Researchers used mass spectrometry to measure oxygen consumption and carbon dioxide production in washed yeast cell suspensions supplemented with glucose. Adding ammonium chloride to aerobic cultures substantially increased CO2 evolution from glycolysis and slightly stimulated respiration across all three organisms. Importantly, the ammonium ion effect was distinct from two other regulatory mechanisms: the stimulatory effect of CCCP (an uncoupler of aerobic energy production) and the Pasteur effect (oxygen-mediated inhibition of glycolysis). The authors propose that ammonium ions activate phosphofructokinase, a key glycolytic enzyme, and that the transient nature of the effect may reflect consumption of ammonium for amino acid and protein synthesis. The additive nature of these different metabolic effects suggests that maximal enzyme activation requires multiple regulatory signals. These findings have implications for understanding fermentation dynamics, particularly regarding ethanol production in media with high ammonium concentrations.

Key findings

• Addition of NH4+ to yeast suspensions greatly increased glycolytic CO2 production and slightly stimulated respiration in all three yeast species tested
• The ammonium ion effect is mechanistically distinct from both the Pasteur effect and uncoupler-mediated stimulation of metabolism
• The ammonium ion effect likely works through activation of phosphofructokinase and is transient, possibly due to consumption of ammonium for biosynthesis
• The stimulatory effects of anaerobiosis, uncoupler, and ammonium ions appear to be additive