BIOCHEMICAL BASIS FOR GLUCOSE-INDUCED INHIBITION OF MALOLACTIC FERMENTATION IN LEUCONOSTOC-OENOS

The sugar-induced inhibition of malolactic fermentation in cell suspen sions of Leuconostoc oenos, recently reclassified as Oenococcus oeni ( L. M. T. Dicks, F. Dellaglio, and M. D. Collins, Int. J. Syst. Bacteri ol. 45:395-397, 1995) was investigated by in vivo and in vitro nuclear magnetic resonance (NMR) spectroscopy and manometric techniques. At 2 mM, glucose inhibited malolactic fermentation by 50%, and at 5 mM or higher it caused a maximum inhibitory effect of ca. 70%. Galactose, tr ehalose, maltose, and mannose caused inhibitory effects similar to tha t observed with glucose, but ribose and 2-deoxyglucose did not affect the rate of malolactic activity. The addition of fructose or citrate c ompletely relieved the glucose-induced inhibition. Glucose was not cat abolized by permeabilized cells, and inhibition of malolactic fermenta tion was not observed under these conditions. P-31 NMR analysis of per chloric acid extracts of cells obtained during glucose-malate cometabo lism showed high intracellular concentrations of glucose-6-phosphate, 6-phosphogluconate, and glycerol-3-phosphate. Glucose-6-phosphate, 6-p hosphogluconate, and NAD(P)H inhibited the malolactic activity in perm eabilized cells or cell extracts, whereas NADP(+) had no inhibitory ef fect. The purified malolactic enzyme was strongly inhibited by NADH, w hereas all the other above-mentioned metabolites exerted no inhibitory effect, showing that NADH was responsible for the inhibition of malol actic activity in vivo. The concentration of NADH required to inhibit the activity of the malolactic enzyme by 50% was ca. 25 mu M. The data provide a coherent biochemical basis to understand the glucose-induce d inhibition of malolactic fermentation in L. oenos.