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Results for “AMINO ACID METABOLISM”

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At least 775 records · Page 43Linked to original sources
PubMed1976

Effects of hormones on protein and amino acid metabolism in mammary-gland explants of mice.

The effects of insulin, cortisol and prolactin on amino acid uptake and protein biosynthesis were determined in mammary-gland explants from mid-pregnant mice. Insulin stimulated [3H]leucine incorporation into protein within 15 min of adding insulin to the incubation medium. Insulin also had a rapid stimulatory effect on the rate of aminoiso[14C]butyric acid uptake, but it had no effect on the intracellular accumulation of [3H]leucine. Cortisol inhibited the rate of [3H]leucine incorporation into protein during the initial 4h of incubation, but it had no effect at subsequent times. [3H]Leucine uptake was unaffected by cortisol, but amino[14C]isobutyric acid uptake was inhibited after a 4h exposure period to this hormone. Prolactin stimulated the rate of [3H]leucine incorporation into protein when tissues were exposed to this hormone for 4h or more; up to 4h, however, no effect of prolactin was detected. At all times tested, prolactin had no effect on the uptake of either amino[14C]isobutyric acid or [3H]leucine. Incubation with actinomycin D abolished the prolactin stimulation of protein biosynthesis, but this antibiotic did not affect the insulin response. A distinct difference in the mechanism of action of these hormones on protein biosynthesis in the mammary gland is thus apparent.

Aminoisobutyric Acids↗
PubMed1998

Infusion of soy and casein protein meals affects interorgan amino acid metabolism and urea kinetics differently in pigs.

For routine evaluation of the quality of dietary protein, amino acid scoring patterns were used. Evaluation of this pattern for soy and casein revealed that these proteins are of almost equal quality. However, in vivo studies showed a large difference. To study the biological effects of meals with casein and soy protein, the contributions of individual amino acids to net protein retention and amino acid kinetics in gut, liver and muscle in healthy pigs were investigated. Isonitrogenous enteral nutrition, infused at a rate of 10 mL. kg body wt-1. h-1 and consisting of maltodextrin (137 g/L) with added casein (53 g/L) or soy protein (68 g/L), was given to conscious, healthy female multicathetized pigs (20-22 kg, n = 12). A primed-constant infusion protocol with L-[ring-2,6-3H]phenylalanine, L-[3,4-3H]valine and [15N-15N]urea was used to measure amino acid and urea kinetics in gut, liver and muscle. Measurements were done postabsorptively and 2-6 h after initiation of the enteral nutrition. During the meal, appearance of amino acids into the portal vein and the uptake by the liver was lower with casein infusion. Muscle uptake did not differ. Gut protein synthesis tended to be lower with soy infusion (P = 0.1). Liver protein synthesis and degradation were higher with casein infusion (P < 0.05), while in muscle, soy infusion stimulated protein turnover (P < 0.05). In comparison to the postabsorptive condition, liver urea production was unchanged after casein infusion, while it was significantly increased after soy infusion. These results suggest that the quality of soy protein is inferior to that of casein protein.

Amino Acids↗
PubMed1975

[Free amino acids and some enzymes of placental amino acid metabolism at different stages of its development].

There were revealed changes in the content of free amino acids and in the activity of glutamic dehydrogenase, aspartic- and alanine-aminotransferases in the course of development of the placenta in guinea pigs. The greatest values by the indices under study were reached by the 25th--30th days of pregnancy, i.e. by the period of final formation of the placenta. By the 40th day of pregnancy the activity of the enzymes and the content of free amino acids fell, and from the 45th day persisted at a certain stable level up to the occurrence of labour.

Alanine Transaminase↗
PubMed1989

[Changes in amino acid metabolism at the onset of colchicine resistance in Dzungarian hamster fibroblast cell culture].

We have studied amino acid up-take from incubation media by colchicine-resistant and colchicine-sensitive Djungarian hamster fibroblast cells. It has been shown that arginine and asparagine amino acid contents in the medium are different for colchicine-sensitive and colchicine-resistant cells. Amino acids concentration is not reduced in the medium after incubation of resistant cells, while it is decreased after incubation of sensitive cells. We can suggest that penetration of low-weight sources of nitrogen into sensitive cells is hampered. It can also be suggested that protein macromolecules are the main source of nitrogen for these cells. The protein up-take levels from the incubation medium, as assessed by the ammonia and amino acid contents of cell counts don't exceed 5% of their initial concentrations in the medium.

Amino Acids↗
PubMed2005

Thermococcus profundus 2-ketoisovalerate ferredoxin oxidoreductase, a key enzyme in the archaeal energy-producing amino acid metabolic pathway.

2-Ketoisovalerate ferredoxin oxidoreductase (VOR) is a key enzyme in hyperthermophiles catalyzing the coenzyme A-dependent oxidative decarboxylation of mainly aliphatic amino acid-derived 2-keto acids. The very oxygen-labile enzyme purified under anaerobic conditions from a hyperthermophilic archaeon, Thermococcus profundus, is a hetero-octamer (alphabetagammadelta)(2) consisting of four different subunits, alpha = 45,000, beta = 31,000, gamma = 22,000 and delta = 13,000, respectively. Electron paramagnetic resonance and resonance Raman spectra of the purified enzyme indicate the presence of approximately three [4Fe-4S] clusters per alphabetagammadelta-protomer, although one of the clusters has a tendency to be converted to a [3Fe-4S] form during purification. The optimal temperature for the enzyme activity is 93 +/- 2 degrees C and the cognate [4Fe-4S] ferredoxin serves as an electron acceptor of the enzyme. The purified enzyme is highly oxygen-labile (t(1/2), approximately 5 min at 25 degrees C), and is partly protected in the presence of magnesium ions, thiamine pyrophosphate and sodium chloride (t(1/2), approximately 25 min at 25 degrees C).

Amino Acids↗
PubMed1989

Protein and amino acid metabolism in uremia: influence of metabolic acidosis.

Loss of lean body mass occurs frequently in patients with acute or chronic renal failure, but the mechanism(s) causing this abnormality are unknown. Using animal models of experimental uremia, it was found that excess lactate formation in muscle is directly related to the rate of protein breakdown. This suggests that abnormal energy metabolism may be one mechanism for protein wasting. A second mechanism involves metabolic acidosis. Metabolic acidosis activates the catabolism of protein and amino acids in muscle of uremic rats independently of azotemia. Defects in sodium transport by Na,K-ATPase and the Na/K/Cl cotransport system suggest that intracellular ions including hydrogen may be abnormal. If this were the case, uremia would increase the susceptibility to the catabolic effect of metabolic acidosis.

Acidosis↗
PubMedDate not supplied

Branched-chain amino acids metabolic support in surgical patients: a randomized, controlled trial in patients with subtotal or total gastrectomy in 16 Japanese institutions.

A prospective, randomized, controlled trial of nutritional effects of branched-chain-enriched amino acid (BCAA) solution was undertaken in 173 surgical patients with gastric cancer. Eighty-six and 87 patients underwent subtotal and total gastrectomy, respectively. The effects were evaluated in total parenteral nutrition (TPN) in an isocaloric/isonitrogenous setting where the major difference between the group was the amount of BCAA received. Each 80 patients in the control and the BCAA groups completed the trial. The group receiving BCAA-enriched amino acid solution demonstrated a statistically significant improvement on days 2 and 3 in nitrogen balance in patients with total gastrectomy. Three-methyl-histidine excretion gradually decreased after day 1, and the values on day 7 were significantly lower than those on day 1 in the BCAA group in both those receiving subtotal and total gastrectomy. There were no significant differences of serum albumin and rapid turnover proteins between the control and BCAA groups in both those receiving subtotal and total gastrectomy. Plasma BCAA level and BCAA to aromatic amino acid (AAA) ratio were significantly higher, and AAA level was significantly lower in the BCAA group than in the control group. There were no serious complications encountered during the observation period in both groups. These results indicated that a BCAA-enriched amino acid solution can improve metabolism and maintains good nitrogen retention without increasing side effects as compared with a conventional amino acid solution for nutritional support of patients who have received subtotal or total gastrectomy.

Adolescent↗
PubMed1983

Effects of parathyroid hormone on skeletal muscle protein and amino acid metabolism in the rat.

Because prominent skeletal muscle dysfunction and muscle wasting are seen in both chronic uremia and in primary hyperparathyroidism, and because markedly elevated parathyroid hormone levels occur in both disorders, potential effects of parathyroid hormone on skeletal muscle protein, amino acid, and cyclic nucleotide metabolism were studied in vitro using isolated intact rat epitrochlearis skeletal muscle preparations. Intact bovine parathyroid hormone and the synthetic 1-34 fragment of this hormone stimulated the release of alanine and glutamine from muscle of control but not from chronically uremic animals. This stimulation was dependent upon the concentration of parathyroid hormone added: At 10(5) ng/ml parathyroid hormone increased alanine release 84% and glutamine release 75%. Intracellular levels of alanine and glutamine were not altered by parathyroid hormone. Increasing concentrations of the 1-34 polypeptide decreased [(3)H]leucine incorporation into protein of muscles from both control and uremic animals. Using muscles from animals given a pulse-chase label of [guanido-(14)C]arginine in vivo, parathyroid hormone increased the rate of loss of (14)C label from acid-precipitable protein during incubation and correspondingly increased the rate of appearance of this label in the incubation media. Parathyroid hormone increased muscle cAMP levels by 140% and cGMP levels by 185%, but had no effect on skeletal muscle cyclic nucleotide phosphodiesterase activities as assayed in vitro. Adenylyl cyclase activity in membrane preparations from control but not uremic rats was stimulated by parathyroid hormone in a concentration-dependent fashion. However, no stimulation of guanylyl cyclase activity was noted by parathyroid hormone, although stimulation by sodium azide was present. Incubation of muscles with added parathyroid hormone produced a diminished responsiveness towards epinephrine or serotonin regulation of amino acid release and cAMP formation in the presence compared to the absence of parathyroid hormone. In the absence of parathyroid hormone, detectable inhibition of alanine and glutamine release was produced by 10(-9) M epinephrine, whereas in the presence of parathyroid hormone (1,000 ng/ml) inhibition of alanine and glutamine release required 10(-6) M or greater epinephrine. Resistance to cyclic AMP action as well as inhibition of cyclic AMP formation by parathyroid hormone was found. Preincubation of rat sarcolemma with 1-34 parathyroid hormone produced a decreased activity of the isoproterenol-stimulable adenylyl cyclase activity but there was no apparent change in the concentration of isoproterenol required for one-half maximal and maximal stimulation of the enzyme. These findings suggest that high levels of parathyroid hormone have direct effects on skeletal muscle protein, amino acid, and cyclic nucleotide metabolism in muscle of normal but not uremic animals. Treatment with these high levels of parathyroid hormone in vitro appears to reproduce in normal muscle, the metabolic deficits and loss of hormone responsiveness observed in muscle of chronically uremic animals. It is therefore possible that direct effects of parathyroid hormone on skeletal muscle may account in part for the muscle dysfunction and wasting of primary hyperparathyroidism and chronic uremia.

Adenylyl Cyclases↗