R. Tourdotmarechal et al., TRANSPORT OF MALIC-ACID IN LEUCONOSTOC-OENOS STRAINS DEFECTIVE IN MALOLACTIC FERMENTATION - A MODEL TO EVALUATE THE KINETIC-PARAMETERS, Applied microbiology and biotechnology, 39(4-5), 1993, pp. 499-505
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.