TRANSPORT OF MALIC-ACID IN LEUCONOSTOC-OENOS STRAINS DEFECTIVE IN MALOLACTIC FERMENTATION - A MODEL TO EVALUATE THE KINETIC-PARAMETERS

Two Leuconostoc oenos mutant strains unable to metabolize malic acid w ere differentiated by U-C-14!-labelled L-malate transport assays into a malolactic-enzyme-deficient mutant and a malate-transport-defective mutant. A mathematical analysis of the data froM L-malic acid uptake at three pH values (5.2, 4.5, and 3.2) in the malolactic-enzyme-defici ent strains suggests two simultaneous uptake mechanisms, presumably a carrier-mediated transport and a passive diffusion for the anionic and the undissociated forms of the acid, respectively. The apparent affin ity constant (K(m')) and the maximal rate (V(m')) values for L-malate active transport were, 12 mM and 43 mumol L-malate.mg-1.s-1, respectiv ely. Active transport was constitutive and strongly inhibited by proto nophores and by ATPase inhibitors. L-Lactic acid appeared to inhibit L -malic acid transport, suggesting an L-lactate/L-malate exchange. At p H values of 4.5 or above, the passive diffusion Of L-malic acid was ne gligible. However, at pH 3.2, the mean pH of wine, the permeability of the cells to the undissociated acid by simple diffusion could represe nt more than 50% of total L-malic acid uptake, with a diffusion consta nt (K(D)) Of 0.1 S-1.