Lactate, efflux

Juel, C. (1988), Intracellular pH recovery and lactate efflux in mouse soleus muscles stimulated in vitro The involvement of sodium/proton exchange and a lactate carrier. Acta Physiol. Scand. 132,... 

J. H. Xia and J. K. M. Roberts, Improved cytoplasmic pH regulation, increased lactate efflux, and reduced cytoplasmic lactate levels are biochemical traits expressed in root tips of whole maize seedlings acclimated to a low-oxygen environment. P/anr P/iy.vto/. 105 651 (1994). 

Ten Brink, B., Otto, R., Hansen, U.P., and Konings, W.N. 1985. Energy recycling by lactate efflux in growing and nongrowing cells of Streptococcus cremoris. J. Bacteriol. 162, 383-390. 

Apart from the fermentation, other processes are known, which may contribute to the apparent high ATP yields in propionibacteria. For instance, translocation of a metabolite, if coupled with transmembrane proton movements, can significantly augment the protonmotive force that drives the ATP synthesis, e.g., lactate efflux in a symport with protons in lactic acid bacteria. 

Protein synthesis Glycogen synthesis Lactate uptake Amino acid uptake Glutaminase Glycine oxidation Ketoisocaproate oxidation Acetyl-CoA carboxylase Urea synthesis from amino acids Glutathione (GSH) efflux Taurocholate excretion into bile Actin polymerization Microtubule stability Lysosomal pH... 

Koh JY, Choi DW (1987) Quantitative determination of glutamate mediated cortical neurontil injury in cell culture by lactate dehydrogenase efflux assay. J Neurosd Methods 20 83—90 Koh JY, Choi DW (1994) Zinc toxicity on cultured cortical neurons involvement of N-methyl-D-aspartate receptors. Neuroscience 60 1049-1057... 

Cassidy, C.J., Phillis, J.W., and O Regan, M.H. (2001) Further studies on the effects of topical lactate on amino acid efflux from the ischemic rat cortex. Brain Research, 901, 30-37. 

Secondly, the transport inhibitor must be able to pass the cell membrane. The inability of benzene-1,2,3-tricarboxylate to inhibit gluconeogenesis from lactate in perfused pigeon liver, a tissue in which mitochondrial efflux of phosphoenolpyruvate is obligatory for glucose synthesis, is presumably due to lack of penetration through the plasma membrane [16], This observation is interesting since it shows that the ability of an inhibitor to penetrate the cell membrane may vary from tissue to tissue benzene-1,2,3-tricarboxylate does inhibit lipogenesis in hepatocytes of neonatal chicks, as discussed above. Another example is the apparent relative impermeability of the plasma membrane of isolated foetal rat hepatocytes, as compared with that from adult rats, for atractyloside, the inhibitor of the adenine nucleotide translocator [17]. 

Mitochondrial aspartate efflux is important in processes like urea synthesis [90], gluconeogenesis from lactate and the transport of cytosolic reducing equivalents to the mitochondria via the so-called malate-aspartate shuttle, e.g. during ethanol oxidation and gluconeogenesis from reduced substrates like glycerol, sorbitol, and xylitol [4,5]. During gluconeogenesis from lactate oxaloacetate is transported to the cytosol as aspartate to circumvent the low permeability of the mitochondrial membrane for oxaloacetate. 

Fig. 11. Synthesis of ATP by substrate level phosphorylation and the generation of A/ii] by lactate-proton efflux during honaolactic fermentation.

Recent evidence suggests that excretion of ochratoxin A into human milk is mediated by breast cancer resistance protein (BCRP). BCRP is a member of the ATP-dependent efflux transporter family, which is highly expressed during lactation in various species, including humans, and is known to be responsible for the excretion of various drugs and xenobiotics into milk (Jonker et al., 2005 Schrickx... 

Figure 8. Metabolic network used for calculating the indicated flux values from the data in Figure 7. Abbreviations additional to those defined in Fig. 6 are Fl, efflux of lactate F, fumarate F influx of C-propionate.

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