The Kinetics of Pyridine Nucleotide Reduction following the Addition of Glucose to Bakers' Yeast

Changes of pyridine nucleotide concentration in yeast followingthe addition of glucose have been measured by a fluorimetricassay applied to cell extracts. The major changes were in nicotinamideadenine dinucleotide (NAD) which, during the first minute afterglucose addition, was rapidly reduced and then more slowly reoxidized.Later, one to two minutes after adding glucose, NAD was reducedagain to a steady-state value. No NAD was reduced when acetaldehydewas added simultaneously with glucose. The oxidation of NAD,which followed the initial reduction, was slowed down by sodiumfluoride and almost completely abolished by sodium sulphite.The initial reduction of NAD is ascribed to 3-phosphoglyceraldehydedehydrogenase and its subsequent oxidation is ascribed to alcoholdehydrogenase. Probably only that NAD bound to 3-phosphoglyceraldehydedehydrogenase is reduced initially. The reasons for these viewsare discussed.