Uptake of a Series of Neutral Dipeptides Including l-Alanyl-l-Alanine, Glycylglycine and Glycylsarcosine by Hamster Jejunum in Vitro

1984 ◽  
Vol 67 (5) ◽  
pp. 541-549 ◽  
Author(s):  
D. M. Matthews ◽  
D. Burston
Keyword(s):  
Amino Acids ◽  
Free Amino ◽  
Inhibitory Effect ◽  
Progressive Increase ◽  
The Other ◽  
Uptake System ◽  
Apparent Affinity ◽  
Inhibitory Ability ◽  
Kinetics Of

1. This paper is the last of a set reporting an investigation of the kinetics of jejunal uptake and inhibitory ability of a series of neutral dipeptides, glycylglycine, l-ananyl-l-alanine, l-valyl-l-valine and l-leucyl-l-leucine, with progressively longer and more lipophilic side chains. 2. The results suggested that at pH 5, uptake of l-alanyl-l-alanine, like that of l-valyl-l-valine and l-leucyl-l-leucine, was the result of two processes, uptake of intact peptide and uptake of free amino acid released extracellularly. On the other hand, uptake of glycylglycine was entirely in the form of intact peptide. In contrast to uptake of l-valyl-l-valine and l-leucyl-l-leucine, the proportion of intact l-alanyl-l-alanine taken up by mediated transport was greatest at the lowest concentration studied and smallest at the highest concentration. 3. Taking the series of results as a whole, whereas the corresponding series of amino acids, glycine, l-alanine, l-valine and l-leucine, showed a progressive increase in apparent affinity for uptake and a decrease in Vmax., we could find no such regular progression with the peptides. 4. The results of work on inhibition of uptake of one dipeptide by another were unexpectedly complex. Examples were the very powerful inhibitory effect of l-valyl-l-valine on uptake of glycylsarcosine, not suggested by the Kt of the former peptide, and the failure of glycylsarcosine to cause complete inhibition of uptake of l-alanyl-l-alanine and l-leucyl-l-leucine, though it could completely inhibit uptake of l-valyl-l-valine. There may be more than one uptake system for intact peptides, but we cannot yet suggest an explanation for all the results on inhibitions of uptake.

Uptake of l-Leucyl-l-Leucine and Glycylsarcosine by Hamster Jejunum in Vitro

1983 ◽  
Vol 65 (2) ◽  
pp. 177-184 ◽  
Author(s):  
D. M. Matthews ◽  
D. Burston
Keyword(s):  
Amino Acid ◽  
Intestinal Transport ◽  
Inhibitory Effect ◽  
Complete Inhibition ◽  
Maximal Velocity ◽  
Uptake System ◽  
Apparent Affinity ◽  
Kinetics Of Uptake ◽  
Dipeptide Uptake

1. Preliminary observations of the effects on intestinal transport of the lipophilic properties of the amino acid side chains of a series of neutral dipeptides showed that, contrary to expectation, l-valyl-l-valine and not l-leucyl-l-leucine was the most powerful inhibitor of uptake of the hydrolysis-resistant dipeptide glycylsarcosine by hamster jejunum in vitro. 2. Investigation of the kinetic characteristics of uptake of l-leucyl-l-leucine showed that Kt and Vmax. were lower than the corresponding values for l-valyl-l-valine, suggesting a higher apparent affinity for transport and a lower maximal velocity of transport. Ki for the inhibitory effect of l-leucyl-l-leucine on uptake of glycylsarcosine was less than one-half of the Kt for l-leucyl-l-leucine, so that inhibition was stronger than that expected from the apparent affinity for transport obtained from the kinetics of uptake of the inhibitor. In spite of this, l-leucyl-l-leucine was a much less powerful inhibitor of uptake of glycylsarcosine than was l-valyl-l-valine. 3. The results suggest that total uptake of l-leucyl-l-leucine at pH 5 is the result of at least two processes: uptake of intact peptide by one or more mechanisms, and also hydrolysis followed by uptake of free amino acid. At most concentrations, more than half the mediated uptake of l-leucyl-l-leucine was in the form of intact peptide. 4. The results of experiments on competition for uptake between dipeptides were unexpected. l-leucyl-l-leucine could inhibit mediated uptake of intact glycylsarcosine completely, but glycylsarcosine could not cause complete inhibition of mediated uptake of intact l-leucyl-l-leucine. Glycylsarcosine could, however, cause complete inhibition of mediated uptake of intact l-valyl-l-valine, which in turn could cause complete inhibition of mediated uptake of intact l-leucyl-l-leucine. The existence of more than one dipeptide uptake system in the small intestine seems probable.

Kinetics of Influx of Peptides and Amino Acids into Hamster Jejunum in Vitro: Physiological and Theoretical Implications

1990 ◽  
Vol 79 (3) ◽  
pp. 267-272 ◽  
Author(s):  
D. Burston ◽  
D. M. Matthews
Keyword(s):  
Amino Acids ◽  
Free Amino Acids ◽  
Free Amino ◽  
Transport Rate ◽  
Side Chain ◽  
Neutral Amino Acids ◽  
Acidic Amino Acids ◽  
Wide Range ◽  
Kinetics Of

1. This paper reports a comparison of the kinetics of influx into hamster jejunum of a series of dipeptides of neutral, basic and acidic amino acids, and a tripeptide of neutral amino acids, with those of corresponding free amino acids. 2. Kt, the substrate concentration at which the transport rate is half the maximal transport rate, and Vmax, the maximal transport rate, were more similar from one peptide to another than among amino acids, with the result that, over a wide range of concentrations, rates of influx of individual peptides varied much less than those of amino acids. 3. It is suggested that this may account for the rates of absorption of amino acids being closely related to the amino acid composition of the protein fed, instead of being widely dissimilar as with corresponding mixtures of free amino acids. 4. With neutral amino acids, both Kt and Vmax. fell with increasing length of the side-chain, as observed on many previous occasions. This did not occur with the corresponding homologous dipeptides, which shows that the hypothesis that the apparent affinity for transport is related to the lipophilic properties of the side-chain cannot be applied to peptides.

ACTION OF THYROTROPHIN (TSH) ON THYROID PROTEIN SYNTHESIS IN VIVO AND IN VITRO

1973 ◽  
Vol 72 (3) ◽  
pp. 453-463 ◽  
Author(s):  
Gustav Wägar ◽  
Ragnar Ekholm ◽  
Ulla Björkman
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Free Amino ◽  
Microsomal Fraction ◽  
Inhibitory Effect ◽  
Leucine Incorporation ◽  
Bovine Thyroid ◽  
Stimulation Of

ABSTRACT The effect of TSH on the incorporation of L-14C-leucine into thyroid proteins was studied in vivo in rats as well as in vitro on bovine thyroid slices and a microsomal subfraction. It was found that TSH reduced the incorporation of radio-leucine into the proteins of slices during the first 2 hours when the concentration of non-labelled leucine in the incubation medium was low. When cold leucine was added to the medium this inhibitory effect was no longer observed. After 6 hours a stimulatory effect on the radio-leucine incorporation by TSH was obvious at both low and high leucine concentrations. The incorporation of 14C-leucine into proteins by the microsomal fraction incubated with a pH 5-fraction was reduced by TSH but this inhibitory effect of TSH disapperaed when post-microsomal supernatant, containing free amino acids, was added to the incubation mixture. It is suggested that the apparent inhibitory effect of TSH on protein synthesis in thyroid slices is due to an altered ratio labelled/non-labelled leucine, caused by stimulation of proteolysis by TSH. This explanation does not seem applicable, however, to the similar apparently inhibitory effect of TSH on protein synthesis observed in the microsomal fraction. In the in vivo experiments a stimulation of the incorporation of labelled leucine could not be observed until 4 hours after the TSH administration. It is suggested that this apparently slow effect of TSH on protein synthesis might be explained either by an indirect effect of TSH on protein synthesis or by a TSH-induced change of the ratio labelled/non-labelled leucine.

Turnover of total proteins and ornithine aminotransferase during liver regeneration in rats

1980 ◽  
Vol 238 (1) ◽  
pp. E46-E52
Author(s):  
S. L. Augustine ◽  
R. W. Swick
Keyword(s):  
Amino Acids ◽  
Liver Regeneration ◽  
Protein Degradation ◽  
Partial Hepatectomy ◽  
Free Amino ◽  
Liver Protein ◽  
Ornithine Aminotransferase ◽  
Fractional Rate

The recovery of approximately 40% of the total liver protein during the first day after partial hepatectomy was shown to be due to the near cessation of protein breakdown rather than to an increase in protein synthesis. The decrease in degradation of total protein was less if rats were adrenalectomized or protein-depleted prior to partial hepatectomy. The effect of these treatments originally suggested that changes in free amino acid levels in liver might be related to the rate of protein degradation. However, no correlation was found between levels of total free amino acids and rates of breakdown. Measurements of individual amino acids during liver regeneration suggested that levels of free methionine and phenylalanine, amino acids that have been found to lower rates of protein degradation in vitro, are not correlated with rates of breakdown in vivo. The difference between the fractional rate of ornithine aminotransferase degradation (0.68/day and 0.28/day in sham-hepatectomized and partially hepatectomized rats, respectively) was sufficient to account for the higher level of this protein 3 days after surgery in the latter group.

scholarly journals Identification in skeletal muscle of a distinct extracellular pool of amino acids, and its role in protein synthesis

1971 ◽  
Vol 121 (5) ◽  
pp. 817-827 ◽  
Author(s):  
R. C. Hider ◽  
E. B. Fern ◽  
D. R. London
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Incubation Medium ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Longus Muscle ◽  
Kinetics Of

1. The kinetics of radioactive labelling of extra- and intra-cellular amino acid pools and protein of the extensor digitorum longus muscle were studied after incubations with radioactive amino acids in vitro. 2. The results indicated that an extracellular pool could be defined, the contents of which were different from those of the incubation medium. 3. It was concluded that amino acids from the extracellular pool, as defined in this study, were incorporated directly into protein.

Effects of abomasal infusions of sodium caseinate, a hydrolysate of casein or a corresponding mixture of free amino acids on milk yield and composition in dairy cows

1995 ◽  
Vol 62 (1) ◽  
pp. 29-37 ◽  
Author(s):  
Jai-Jun Choung ◽  
David G. Chamberlain
Keyword(s):  
Amino Acids ◽  
Dairy Cows ◽  
Free Amino Acids ◽  
Free Amino ◽  
Milk Protein ◽  
Bioactive Peptides ◽  
Basal Diet ◽  
Sodium Caseinate ◽  
Amino Acid Residues ◽  
Kinetics Of

SummaryThe effects of the form in which amino acids are presented to the abomasum on the milk production of dairy cows receiving a basal diet of grass silage and a barley-based supplement were examined in two experiments. Effects of abomasal infusions of sodium caseinate were compared with the effects of corresponding levels of either an enzymic hydrolysate of casein (Expt 1) or a corresponding mixture of free amino acids (FAA; Expt 2). In Expt 1, although the yield of protein in milk increased progressively with each level of infusion, the yields of protein were greater for the caseinate than for the hydrolysate. Again, in Expt 2, for milk protein yield, sodium caseinate was superior to FAA at the lower level of infusion. In both experiments, the hydrolysate and FAA treatments were associated with higher concentrations of fat in the milk. There were indications of differences in the pattern of secretion of glucagon between the caseinate and FAA treatments. It is concluded that the differences between treatments relate either to the kinetics of absorption of amino acid residues or to the action of bioactive peptides released during digestion of casein.

scholarly journals 2,4-EPIBRASSIONOLIDE ACTIVATES PRIMING RESISTANCE AGAINST RHIZOPUS STOLONIFER INFECTION IN PEACH FRUIT

2020 ◽  
Vol 49 (2) ◽  
pp. 135-143
Author(s):  
C.H. Li ◽  
M.Y. Du ◽  
K.T. Wang
Keyword(s):  
Fungal Infection ◽  
Inhibitory Effect ◽  
The Other ◽  
Antifungal Compounds ◽  
Rhizopus Stolonifer ◽  
Peach Fruit ◽  
Direct Inhibitory Effect ◽  
Potential Alternative ◽  
Direct Toxicity

This study was conducted to assess the effects of 2,4-epibrassionolide (EBR) on mold decay caused by Rhizopus stolonifer and its capability to activate biochemical defense reactions in postharvest peaches. The treatment of EBR at 5 μM possessed the optimum effectiveness on inhibiting the Rhizopus rot in peach fruit among all treatments. The EBR treatment significantly up-regulated the expression levels of a set of defense-related enzymes and PR genes that included PpCHI, PpGns1, PpPAL, PpNPR1, PpPR1 and PpPR4 as well as led to an enhancement for biosynthesis of phenolics and lignins in peaches during the incubation at 20 °C. Interestingly, the EBR-treated peaches exhibited more striking expressions of PR genes and accumulation of antifungal compounds upon inoculation with the pathogen, indicating a priming defense could be activated by EBR. On the other hand, 5 μM EBR exhibited direct toxicity on fungal proliferation of R. stolonifer in vitro. Thus, we concluded that 5 μM EBR inhibited the Rhizopus rot in peach fruit probably by a direct inhibitory effect on pathogen growth and an indirect induction of a priming resistance. These findings provided a potential alternative for control of fungal infection in peaches during the postharvest storage.

scholarly journals Amino acid regulation of synthesis of ribonucleic acid and protein in the liver of rats

1971 ◽  
Vol 124 (2) ◽  
pp. 385-392 ◽  
Author(s):  
R. W. Wannemacher ◽  
C. F. Wannemacher ◽  
M. B. Yatvin
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Free Amino Acids ◽  
Free Amino ◽  
Cellular Protein ◽  
Deficient Diet ◽  
Cellular Protein Content ◽  
Regulate Protein

Weanling (23-day-old) rats were fed on either a low-protein diet (6% casein) or a diet containing an adequate amount of protein (18% casein) for 28 days. Hepatic cells from animals fed on the deficient diet were characterized by markedly lower concentrations of protein and RNA in all cellular fractions as compared with cells from control rats. The bound rRNA fraction was decreased to the greatest degree, whereas the free ribosomal concentrations were only slightly less than in control animals. A good correlation was observed between the rate of hepatic protein synthesis in vivo and the cellular protein content of the liver. Rates of protein synthesis both in vivo and in vitro were directly correlated with the hepatic concentration of individual free amino acids that are essential for protein synthesis. The decreased protein-synthetic ability of the ribosomes from the liver of protein-deprived rats was related to a decrease in the number of active ribosomes and heavy polyribosomes. The lower ribosomal content of the hepatocytes was correlated with the decreased concentration of essential free amino acids. In the protein-deprived rats, the rate of accumulation of newly synthesized cytoplasmic rRNA was markedly decreased compared with control animals. From these results it was concluded that amino acids regulate protein synthesis (1) by affecting the number of ribosomes that actively synthesize protein and (2) by inhibiting the rate of synthesis of new ribosomes. Both of these processes may involve the synthesis of proteins with a rapid rate of turnover.

Transport of amino acids by isolated gills of the mussel Mytilus californianus Conrad

1975 ◽  
Vol 62 (2) ◽  
pp. 313-325
Author(s):  
S. H. Wright ◽  
T. L. Johnson ◽  
J. H. Crowe
Keyword(s):  
Amino Acids ◽  
Significant Role ◽  
Transport Mechanism ◽  
Surrounding Medium ◽  
Gill Tissue ◽  
Mytilus Californianus ◽  
Animal Nutrition ◽  
Neutral Amino Acids ◽  
Kinetics Of

The unidirectional influx of cycloleucine into in vitro preparations of gill tissue of the mussel, Mytilus californianus, was determined. Influx was found to be linear for at least an hour, and the kinetics of cycloleucine influx conformed to Michaelis-Menten type kinetics. The transport mechanism(s) for cycloleucine is relatively specific for the L-enantiomorph of neutral amino acids, and is capable of accumulating cycloleucine to intracellular concentrations much higher than those of the surrounding medium. Evedence is presented that the transport of amino acids by gill tissue plays a significant role in whole animal nutrition.

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