Uptake of Amino Acids by Cells

Uptake of Amino Acids by Cells 1397 F. Serine and Glycine... 

A rather satisfactory explanation of the irreversibility of amino acid accumulation in yeast cells is that it might result from specific regulatory mechanisms capable of immobilizing the transporters in a closed position. Uptake of amino acids by a number of permeases does indeed appear to be regulated by specific, and possibly allosteric, feedback inhibition. This idea is based on the fact that a number of transport systems seem to be specifically inhibited by their internally accumulated... 

Patterson MK (1972) Uptake and utilisation of amino acids by cell cultures. In Rothblat GH Cristofalo VJ (eds) Growth, Nutrition and Metabolism of Cells in Culture, vol. 1, pp. 171-209. Academic Press, New York. 

Griffiths JB Pirt SJ (1967) The uptake of amino acids by mouse cells (strain LS) during growth in batch culture and chemostat culture the influence of growth rate. Proceedings of the Royal Society of London, Series B 168 421-438. 

Glyphosate has been found to retard uptake of amino acids, nucleotides, and glucose in isolated cells (99), Other studies have indicated that glyphosate-caused inhibition of uptake of amino acids by intact plant roots (71) or excised buds (72) is not severe. 

Determination of y-GT y-GT is a glycoprotein and a membrane-bound enzyme that is located primarily on the outer surface of plasma membrane. y-GT plays a significant role in the glutathione metabolism and the transfer of the y-glutamyl moiety to certain amino acids that may be involved in the uptake of amino acids by a cell. The body s y-GT is present in order of decreasing activity in kidneys (relative activity 100), pancreas (24), and liver (7). The significant elevation of y-GT activity in serum is... 

Arathoon WR, Telling CR (1982), Uptake of amino acid and glucose by BHK-21 clone 13 suspension cells during cell growth, Dev. Biol. Stand. 50 145-154. 

Insulin affects the protein metabolism by an increased uptake of amino acids as a result of the increased permeability of the cell membranes. 

A variety of phytoplankton are known to possess cell surface oxidases (Palenik and Morel, 1990a,b) and extracellular oxidation of amino acids has been shown to occur in nature (Pantoja and Lee, 1994 Mulholland et al., 1998, 2002a). Direct uptake of amino acid-derived N from this process represented up to 4% of the observed NFI4+ uptake in a mid-Adantic estuary (Mulholland et al., 2003). Recently, a cell surface protein expressed under N-limitation was identified as a deaminase suggesting that these enzymes are regulated by cellular N status as for other pathways of N uptake and metabolism (Palenik and Koke, 1995). Failure to account for alternative pathways for mobilization of DON might result in underestimates of its utilization in nature. 

North, B., and Stephens, G. (1971). Uptake and assimilation of amino acids by Platymonas. 2. Increased uptake in nitrogen deficient cells. Biol. Bull. 140, 242—254. 

Insulin stimulates protein biosynthesis by a mechanism which is not directly dependent upon its action in stimulating the uptake and accumulation of amino acids by the cells. Insulin increases the incorporation of amino acids into the protein of a number of tissues, an effect which is dependent on the presence of glucose. 

The first step in protein metabolism in muscle is the uptake of amino acids from the blood by the fibers, via the extracellular space. Experiments with injected amino acids and with isolated muscle preparations by many workers have demonstrated that muscle fibers can accumulate amino acids from the medium. Experiments with a-aminoisobutyric acid, a nonmetabolizable amino acid, have been particularly useful in enabling accumulation to be studied independently of incorporation of the amino acid into protein. An increased accumulation of amino acids has been observed in the dystrophic mouse (B3), in vitamin E deficiency (D4), and in denervated muscle (D4). The authors of the last-mentioned observation concluded from their evidence that the increased accumulation was associated with increased active transport into the muscle cells, not with a change in passive permeability of the membranes. Nichoalds et al. (Nl) found that puromycin, which abolished protein synthesis, had no effect upon the accumulation of glycine- C by control or vitamin E-deficient muscle. More recently, Goldberg and Goodman (G4) observed a decrease in the accumulation of a-aminoisobutyric acid by soleus and plantaris muscles within 3 hours of denervation subsequently. 

In the exocrine pancreatic cells. In many animal cells, the combined force of the Na" concentration gradient and membrane electric potential drives the uptake of amino acids and other molecules against their concentration gradient by lon-llnked symport and antiport proteins (see Section 7.4). And the conduction of action potentials by nerve cells depends on the opening and closing of Ion channels In response to changes In the membrane potential (see Section 7.7). 

Insulin stimulates uptake of glucose and amino acids by cells, glycogen and protein synthesis, and storage of lipids. It inhibits glycogenolysis, gluconeogenesis, breakdovm of stored triglycerides, and ketogenesis. 

Katta Bolic was in a severe stage of negative nitrogen balance on admission, which was caused by both her malnourished state and her intra-abdominal infection complicated by sepsis. The physiologic response to her advanced catabolic status includes a degradation of muscle protein with the release of amino acids into the blood. This release is coupled with an increased uptake of amino acids for "acute phase" protein synthesis by the liver (systemic response) and other cells involved in the immune response to general and severe infection. 

All animal cells studied up to now show the abiUty to accumulate certain amino acids against their concentration gradients, while for sugars such accumulation was only observed in polarized cells, e.g. cells from small intestine or proximal tubule. Ehrlich cells and other tumor cell lines [53-57], tissue culture cells, avian erythrocytes [58], isolated cells and slices from different tissues [59] were studied for their ability to accumulate amino acids. Apart from investigations with epithelia, studies, on Ehrlich cells, of the energetics and mechanism of the accumulative uptake of amino acids play a fundamental role in working out the concept of cotransport between Na and amino acids by animal cells. 

Apart from this use of partition coefficients, uptake of an agent by cells can be forced in another way by using ligands which resemble natural substrates such as amino acids, carbohydrates, choline, purines, and pyrimidines. 

Thus the energy for the active transport of amino acids is derived indirectly from the hydrolysis of ATP (Figure 19.1). After uptake into the absorptive cells by this method, the amino acids pass into the portal circulation by a passive transport process. The brush border membrane contains a number of different transport systems for amino acids, which have overlapping specificity. It is probable that similar systems are responsible for the uptake of amino acids into other tissues such as kidney and liver. As a result of the operation of such transport systems, the total free amino acid concentration in the plasma is kept at between 2 and 4 mM but in the tissues it is between IS and 30 mM. Amino acids derived exogenously fi om the food are mixed with amino acids derived endogenously from the tissues to form a metabolic... 

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