ISSN:
1432-0614
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Abstract Two Leuconostoc oenos mutant strains unable to metabolize malic acid were differentiated by [U-14C]-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-deficient strains suggest 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 affinity constant (K m t) and the maximal rate (V m t) values for L-malate active transport were, 12 mM and 43 μmol L-malate·mg−1·s−1, respectively. Active transport was constitutive and strongly inhibited by protonophores and by ATPase inhibitors. L-Lactic acid appeared to inhibit L-malic acid transport, suggesting an L-lactate/L-malate exchange. At pH values of 4.5 or above, the passive diffusion of L-malic acid was negligible. However, at pH 3.2, the mean pH of wine, the permeability of the cells to the undissociated acid by simple diffusion could represent more than 50% of total L-malic acid uptake, with a diffusion constant (K D) of 0.1 s−1.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00205040
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