Explain the mode of action of fluoride and bisulphate on the fermentation pathway. Predict their likely effect if the yeast treated with these agents had been respiring.
Fluoride ions inhibit alcoholic fermentation by the inhibition of enolase, which is an enzyme functioning in the glycolytic pathway. Enolase catalyzes the reversible dehydration of 2-phospho-D-glycerate to yield PEP (phosphodiesterase).
Fluorides alter the respiration rates by either stimulation of inhibition depending upon the fluoride concentration. Decrease of tissue respiration by fluoride is mainly due to inhibition of respiratory enzymes. Enzymes like Succinic, malic, and NADH dehydrogenases; enolase; phosphoglucomutase, hexokinase and ascorbic acid oxidase are inhibited by fluoride except ATPase. Accumulation of fluoride inhibits ATP forming organelles like chloroplasts, mitochondria, and plasma membrane, ATP synthase enzymes.
In the ethanolic fermentation in yeast may be altered in the presence of sodium sulfite, the acetaldehyde is trapped as a bisulfite addition complex, and glycerol is formed as a major product and acetaldehyde is unable to serve as a hydrogen acceptor.
glucose + HSO3− → glycerol + acetaldehyde-HSO3− + CO2
Dihydroxyacetone phosphate becomes the hydrogen acceptor and started yielding of glycerol-3-phosphate, which is further hydrolyzed to glycerol.