Proton-dependent kinetics of citrate uptake in growing cells of Lactococcus lactis subsp. lactis bv. diacetylactis

Abstract

The kinetic analysis of citrate uptake in growing cells of Lactococcus lactis subsp. lactis biovar. diacetylactis identified a proton‐dependent transport and suggested the divalent anionic species as the form of citrate transported across cell membranes. The reaction followed Michaelis‐Menten kinetics for a two‐substrate reaction. The limiting steps were the formation of the ternary complex and the rate of transport. Temperature modified the activity of the permease, increasing the uptake rate.

The properties of citrate transport catalyzed by CitP of Lactococcus lactis ssp. lactis biovar diacetylactis

“…The highest uptake rates were observed at pH 5.5, whereas at pH values above 6.5 only basal levels of citrate transport were detected. These results are consistent with the assumption of Cachon et al [8] that the divalent anionic species (H-Cit2-) is the form of citrate transported by CitP of L. diacetylactis. Furthermore, the observation that the citrate uptake in resting cells increased about 4fold, when the pH decreased from pH 6.5 to 4.5, agrees with the report of Cachon et al [8] showing that the specific rate values of citrate utilization by growing cells increased 6-fold in the same range of PH.…”

“…Cachon et al [8] developed a mathematical model for citrate bioconversion in L. diacetyluctis based on consumption of citrate by growing cells at different pH values [8]. They found that, in a pH range of 4.5-6.5 were consumption occurs, the affinity constant for the HCi?…”

Kinetic control of oxidation state at thermodynamically buffered potentials in subsurface waters

“…2. In resource-limited settings, common in natural subsurface environments, both abiotic and biotic reaction rates are roughly first order in reactants (Zubay, 1993;Cachon et al, 1995;Stumm and Morgan, 1996). Consequently, oxidants commonly react dominantly with reductants that are present in highest concentration, and vice versa for reductants with oxidants, but only with those satisfying constraint 1.…”

Natural‐abundance isotope ratio mass spectrometry as a means of evaluating carbon redistribution during glucose–citrate cofermentation by Lactococcus lactis

“…This could result from the production rate of diacetyl and acetoin varying throughout the fermentation, reflecting variations in the rate of citrate metabolism relative to that of glucose. Such variation could be induced, for example by changes in pH, as citrate transport (but not glucose transport) is sensitive to this factor [39]. Further analysis of a range of ratios and of the kinetics of the evolution of the δ 13 C acetoin and δ 13 C diacetyl values is required to define this effect.…”