Lactic acid transporters

M. Inuyama, F. Ushigome, A. Emoto, N. Koyabu, S. Satoh, K. Tsukimori, H. Nakano, H. Ohtani, and Y. Sawada. Characteristics of L-lactic acid transport in basal membrane vesicles of human placental syncytiotrophoblast. Am J Physiol. 283 C822-C830 (2002). 

The small intestine contains a wide variety of transporters (amino acid transporters, oligopeptide transporters, glucose transporters, lactic acid transporters etc.) on the apical membrane of the epithelial cells, which serve as carriers to facilitate nutrient absorption by the intestine. On the basolateral membrane, the presence of amino acid and oligopeptide transporters has been demonstrated. Active transport mechanisms for di- and tri-peptides have also been demonstrated in the nasal and buccal epithelia. 

Bienert, G.P., Desguin, B., Chaumont, F., and Hols, P. (2013) Chaimel-mediated lactic acid transport a novel function for aquaglyceroporins in bacteria. Biochem J 454, 559-570. 

The circulatory system carries out many important functions that contribute to homeostasis. It obtains oxygen from the lungs nutrients from the gastrointestinal tract and hormones from the endocrine glands and it delivers these substances to the tissues that need them. Furthermore, it removes metabolic waste products, such as carbon dioxide, lactic acid, and urea, from the tissues. Finally, it contributes to the actions of the immune system by transporting antibodies and leukocytes to areas of infection. Overall, the circulatory system plays a vital role in maintenance of optimal conditions for cell and tissue function. 

Monocarboxylates such as lactic acid and pyruvate are transported across plasma membranes by members of the proton-linked monocarboxylate transporter (MCT)... 

Different organic acids, primarily lactic acid, have been successfully used for decontamination of whole livestock carcasses, and the application of different organic acids used for decontamination has also been tested in the fruit and vegetable industry. Organic acids other than lactic acid that are known to have bactericidal effects are acetic, benzoic, citric, malic, propanoic, sorbic, succinic and tartaric acids (Betts and Everis 2005). The antimicrobial action is due to a reduction in the pH in the bacterial environment, disruption of membrane transport, anion accumulation or a reduction in the internal pH in the cell (Busta et al., 2001). Many fruits contain naturally occurring organic acids. Nevertheless, some strains, for example E. coli 0157, are adapted to an acidic environment. Its survival, in combination with its low infective dose, makes it a health hazard for humans. 

Beyond the transportation sector, biomass is also a promising feedstock for the chemical industry. This industry accounts for 5-10% of today s oil and gas consumption. It may require an even larger fraction in the future as the demand for chemicals has outpaced that for energy in the last few decades. Recently, the chemical industry has indeed showed a significant interest in converting agricultural feedstock into chemical intermediates such lactic acid or propene-l,3-diol. 

K. Hosoya, T. Kondo, M. Tomi, H. Takanaga, S. Ohtsuki, and T. Terasaki. MCT1-mediated transport of L-lactic acid at the inner blood-retinal barrier A possible route for delivery of monocarboxylic acid drugs to the retina. Pharm. Res. 18 1669-1676 (2001). 

An important point to note is that this the above reaction produces lactate, not lactic acid. Nonetheless, protons are produced in glycolysis but in another reaction (Appendix 6.5). Consequently, the two end-products are lactate plus protons, which can be described as lactic acid. Despite this discussion, it can be argued that lactate dehydrogenase is not the terminal reaction of glycolysis, since the lactate plus protons have to be transported out of the cell into the interstitial space. This requires a transporter protein, which transports both lactate and protons across the plasma membrane and out of the cell. 

Although the condition is hypothetical, it can be calculated that if all of the skeletal muscles in the body degraded glycogen to lactic acid at the maximum rate and, if aU of the protons that were produced were transported into the blood, it would exceed the buffering capacity of the blood and the pH would fall dramatically (see below). This could soon result in death. Hence the inhibitory effect of protons... 

A variety of fuels are available to generate ATP for muscle activity phosphocreatine glycogen (which can be converted to lactic acid or completely oxidised to CO2) glucose (from liver glycogen, transported to the muscle via the blood and completely oxidised to CO2) triacylglycerol within the muscle (completely oxidised to CO2) and fatty acids from triacylglycerol in adipose tissue (completely oxidised to CO2). 

Lactic acid Secondary amine LA-2 Sodium carbonate Co transport ofH+ ELM ELM Not done Not done Selectivity studies in relation to acetic, malic, gluconic acid, etc. [46]... 

Lactic acid AmberUte LA-2 NajCOj Co-transport ELM Simplified reac- Reaction controlled transport [46] and... 

Lactic acid Secondary amine Na2C03 and NaOH Co-transport of OH- ELM Model of mass transfer in external layer and internal diffusion in globule pH variation occmred [71]... 

Rhizopus oryzae was immobilized in polyurethane foam cubes by Sun et al. -" The effects of the cube size on cell immobilization, cell growth and L(-i-)-lactic acid production were studied, limnobilization was accomplished by simple adsorption. The use of small cubes for R. oiyzae immobilization was very effective in increasing the productivity of L(-t-)-lactic acid by the immobilized cells. The inoculum size was effective for increasing the immobilization ratio (ratio of the number of cubes containing cells to the total number of cubes). We discussed mass transport problems of polyurethane foam and how the application of certain composite technologies mitigates this difficulty earlier in this chapter. 

Deficiency of pyruvate dehydrogenase is the most frequent cause of lactic acidemia ac Since this enzyme has several components (Fig. 15-15), a number of forms of the disease have been observed. Patients are benefitted somewhat by a high-fat, low-carbohydrate diet. Transient lactic acidemia may result from infections or from heart failure. One treatment is to administer dichloroacetate, which stimulates increased activity of pyruvate dehydrogenase, while action is also taken to correct the underlying illness.d Another problem arises if a lactate transporter is defective so that lactic acid accumulates in muscles.6... 

Lactic acid is the cause of one of many possible disorders in human acid-base metabolism. Lactic acidosis represents an accumulation of lactic acid in the blood and tissues. This condition gradually depletes the natural buffers in the body and there is a consequent lowering of pH. As described in the entry on Glycolysis, lactic acid is the end product til (hat pmcess. Lactic acid blood levels are determined by at least Tour factors. The rate of generation of lactic acid the rate of transport from tissues to plasma and from plasma to the liver (point of utilization of lactic acid) the rate uf utilization and excretion of lactic acid by the kidneys. Normally, all of these funclions are maintained in balance to give a normal blood lactate concentration of about I niFq/l. 

The human body is about 70 percent water. Water is involved in nearly every body process, including digestion, absorption, circulation, and excretion. Blood is about 90 percent water it transports nutrients to the cells and washes out lactic acid and other waste products. 

When Creatine is ingested 45-90 minutes before a work-out, an athlete can take advantage of the training induced increases in blood flow to muscle tissue to transport essential nutrients across muscle cell membranes. (This also acts as a buffer to lactic acid) Since high intensity work-outs trigger the release of adrenal hormones such as Epinephrine and Norepinephrine, the cellular uptake of nutrients is improved. Remember, Ephedrine increases cellular uptake Well Ephedrine is an Epinephrine Mimicker. 

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