Amino acids uptake

Increased protein synthesis Increased amino acid uptake/increased translation of mRNA Akt-mediated stimulation of system A amino acid transporter and stimulation of mRNA-translation through activation of p70S6kinase and elongation initiation factor 4 (elF4). Possible involvement of atypical PKCs... 

Five structural genes for amino acid uptake systems have been cloned in Saccharomyces cerevisiae by functional complementation, and their putative amino acid sequences deduced from the respective nucleotide sequences (Fig. 2). 

Feedback inhibition of amino acid transporters by amino acids synthesized by the cells might be responsible for the well known fact that blocking protein synthesis by cycloheximide in Saccharomyces cerevisiae inhibits the uptake of most amino acids [56]. Indeed, under these conditions, endogenous amino acids continue to accumulate. This situation, which precludes studying amino acid transport in yeast in the presence of inhibitors of protein synthesis, is very different from that observed in bacteria, where amino acid uptake is commonly measured in the presence of chloramphenicol in order to isolate the uptake process from further metabolism of accumulated substances. In yeast, when nitrogen starvation rather than cycloheximide is used to block protein synthesis, this leads to very high uptake activity. This fact supports the feedback inhibition interpretation of the observed cycloheximide effect. 

FRET-based nanosensors have been successfully used to monitor steady state levels of metabolites, nutrients, and ions in mammalian cells [74, 87], Recently FRET-based glucose, sucrose, and amino acid nanosensors have been developed to study the metabolism of glucose, sucrose, and amino acid uptake and metabolism in plant cells [80,89, 91]. The enormous potential of these nanosensors will be crucial for understanding ion (e.g., calcium), metabolite (e.g., sugars), hormone (e.g., auxins, gibberellins etc.), and nutrient (e.g., nitrogen, potassium, phosphorus) requirements and homeostasis in living plant tissues. 

Transgenic tobacco suspensions supplemented with a cocktail of essential and non-essential amino acids produced three-fold more IgG-2b/K antibody than untreated cultures [62]. The amino acids were added 10 h prior to harvesting of the cultures in the presence of 1 mM CaCl2 to facilitate amino acid uptake. 

Insulin promotes amino acid uptake and protein formation. AKT, noted above, is also implicated in mechanisms which regulate protein synthesis. Acting via GSK-3 again, under basal conditions, GSK-3 phosphorylates a key protein translation regulator (called eIF2B). Thus, if GSK-3 is inactivated, eIF2B is not phosphorylated and mRNA translation is permitted. 

Morphologically, this is demonstrated by the development of a multinuclear syncytium with apical microvilli [49], while functional differentiation is associated with induction and synthesis of hormones, such as human chorionic gonadotropin (hCG) and human placental lactogen (hPL) [50, 51]. Cultures of primary cytotrophoblasts have been used to study functional expression of P-gp, amino acid uptake, and hormonal stimulation of amino acid uptake and... 

Amino Acid Uptake. If susceptible leaves are exposed to ozone and then incubated in leucine-U- C, treated leaves absorb this amino acid at a faster rate than controls (Fig. 2). If, after U hr of continuous uptake the C-leucine is followed with nonlabelled leucine, a significant differential utilization of the incorporated leucine is not observed (Fig. 2). This suggests that the greater uptake is not a consequence of more rapid utilization and that it is probably attributable to increased permeability. 

As noted with the amino acid uptake data, a logarithmic plot of deoxyglucose uptake yields a straight line (Fig. 5). There is less uptake immediately after exposure of treated tissue, but after 24 hr a 2- to 3-fold greater uptake is noted. Subsequent experiments confirmed that 2-deoxyglucose is not metabolized therefore, increased uptake can be attributed to increased permeability and transport rather than to greater internal utilization. 

Temperature-Dependence of Amino Acid Uptake in Soybean. The uptake of amino acids by plants into the soluble pool can be an energy-requiring process (52-54), as is the support of protein synthesis. We wished to show the temperature-dependence of influx of amino acids into soybean trifoliate leaf discs taken from control and ozonated seedlings in order to confirm this for the present system. Table II shows that amino acid influx during 30 min was reduced by the lowered temperature by about 70%, and protein synthesis by about 85%, when labelling of control discs proceeded at ice bath temperatures. Qualitatively similar reductions occurred in discs taken from ozonated (50 5 pphm,... 

Thus, we assumed that the system of amino acid uptake into the soybean pools with which we were working was predominantly energy-dependent. 

This kind of experiment was performed in an attempt to show that reduction in labelled amino acid uptake into the soluble pool, observed after as little as 15 min of ozonation (Fig. 6), could be an early or primary event in ozone damage to the soybean trifoliate leaf. It was necessary in this case for the pools to be loaded with unlabelled casein hydrolysate after treatment of the plant, in order to maintain vivo ozone treatment and because it has been reported that high endogenous amino acid levels can confer a degree of resistance to ozone damage (14, 15). 

Amino acid uptake into epithelial cells of the intestinal lumen is mediated by... 

Increased protein synthesis A spurt in amino acid uptake and protein synthesis occurs in the absorptive period after ingestion of a meal containing protein (see Figure 24.6, and 0). This synthesis replaces protein degraded since the previous meal. 

With activity Enzymes, membrane transporters (e.g., amino acid uptake systems, ion pumps)... 

TABLE I Summary of Aquatic Studies That Compared Free Amino Acid Uptake and Bacterial Production... 

Field studies point in a similar direction field comparisons of peptide hydrolysis rates and amino acid turnover in coastal sediments showed that amino acid production could exceed uptake by a factor of approximately 8 (Pantoja and Lee, 1999). A comparison of potential enzyme activities and sedimentary amino acid and carbohydrate inventories in sediments from the Ross Sea also showed that potential hydrolysis rates on time scales of hours should in theory rapidly deplete sedimentary amino acid and carbohydrate inventories (Fabiano and Danovaro, 1998). In deep-sea sediments, Poremba (1995) also found that potential enzyme activities in theory could exceed total sedimentary carbon input by a factor of 200. Finally, Smith et al. s (1992) investigation of potential hydrolysis rates and amino acid uptake in marine snow demonstrated that the particle-associated bacteria were potentially producing amino acids far in excess of their own carbon demand. 

The ratio of oxygen uptake to ammonia excretion in Black Sea mussels has been found to exhibit a distinct daily rhythm (Slatina, 1986). As a rule, the ammonia coefficient (O/N) tends to increase greatly at night. As this rise in energy metabolism does not result from an enhanced locomotor activity, it is difficult to explain or to find any analogue in fish. Farbridge and Leatherland (1987) demonstrated a strong effect of the lunar cycles on amino acid uptake by the scales, also on nucleic acids, metabolic reserves and plasma thyroid hormones in coho salmon. 

Farbridge, K.J. and Leatherland, J.F. (1987). Lunar cycles of coho salmon, Oncorhynchus kisutch. II. Scale amino acid uptake, nucleic acids, metabolic reserves and plasma thyroid hormones. Journal of Experimental Biology 129, 179-189. 

Insulin Promotes glucose and amino acids uptake... 

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