GLUCOSE DEHYDROGENASE OF BACILLUS MEGATERIUM KM COUPLING OF CYTOPLASMIC ENZYME WITH MEMBRANE-BOUND CYTOCHROMES

1. 1. The oxidation of glucose by O2 catalyzed by lysed-cell preparations of Bacillus megaterium KM involves the entire complement of respiratory pigments present in the cell membrane; difference spectra indicate complete reduction of the cytochromes on adding a combination of glucose plus NAD+. 2. 2. The initial step of glucose oxidation occurs in the soluble fraction of the bacterial cell and requires NAD+ or NADP+ as coenzyme. Pyridine nucleotide reduction with either coenzyme is observed in the presence of dialyzed soluble fraction only when substrate is added. Spectral studies of concentrated solutions of the dialyzed soluble fraction indicate total reduction of a flavin component on the addition of only glucose. 3. 3. Lysed protoplast preparations show a negligible respiration rate compared to the rate catalyzed by intact cells. Supplementation with glucose plus NAD+ increases the rate of O2 uptake to a significant fraction of the respiration of intact cells. The data support the conclusion that in this organism, free glucose is oxidized directly via a soluble NAD-linked glucose dehydrogenase (which may involve the participation of a functional endogenous flavin component) coupled to the electron-transport chain of cytochromes. © 1960.