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PubMed1982

[Dependence of intestinal excretion of amino acids on the amino acid content of animal feed. 2. Intestinal excretion of amino acids feeding soybean oil meal].

In an experiment with 20 15N-labelled growing rats the excretion of amino acids and the excretion of metabolic faecal amino acids were investigated after the feeding of soybean oil meal as sole protein source. A low, yet statistically significant increase of the excretion of amino acids and metabolic faecal amino acids was ascertained in accordance with a growing quota of soybean oil meal in the ration. The true digestibility of amino acids ascertained according to conventional methods is above 90% and, under consideration of the increase of metabolic faecal amino acids, on average increases by 3.5 digestibility units (1.4 to 6.2).

Amino Acids↗
PubMed1992

New developments in the synthesis of natural and unnatural amino acids.

Amino acids play an important role in biochemistry and chemistry. They are the building blocks of proteins and play an essential role in the regulation of the metabolism of living organisms. In general, it can be stated that microbial processes (fermentation) are the industrial production methods of choice for large-scale production of naturally occurring proteinogenic L-alpha-H-amino acids, while for the production of synthetic D- and/or L-alpha-H-amino acids, several other methods are highly competitive. At DSM, several routes, i.e., (chemoenzymatic) synthesis, towards L-alpha-H and D-alpha-H-amino acids have been elaborated since the midseventies. A general process for the synthesis of natural as well as synthetic optically pure amino acids has been developed, using an enzymatic kinetic resolution step on racemic amino acid amides as the key step. In this case, both enantiomers of the alpha-H-amino acids are prepared in one single step. This process has been commercialized since 1988. More recent developments using L- or D-amino peptidases in combination with amino acid amide racemases and an asymmetric transformation concept are discussed.

Amino Acid Sequence↗
PubMed2002

Regulation of muscle protein by amino acids.

Amino acid availability is a potent regulator of muscle protein synthesis (MPS). We have performed a series of studies using stable isotope methodology and the arteriovenous balance approach to quantify many aspects of the response of MPS, breakdown, and the balance between synthesis and breakdown to changes in the availability of amino acids. A constant intake of amino acids stimulates MPS in a dose-dependent manner until concentrations are approximately doubled, after which further increases in concentration are ineffective. MPS rises more rapidly after bolus ingestion to a peak rate of MPS higher than during constant intake, but the response is transient. A reduction in amino acid availability below basal levels inhibits MPS. Ingestion of nonessential amino acids is not needed to stimulate MPS. When carbohydrate alone is ingested there is minimal effect on MPS, but there is an interactive effect with amino acid ingestion, meaning the response to amino acids plus glucose is more than the sum of their individual effects. Finally, acute anabolic responses in net MPS correspond quantitatively to differences in 24-h net muscle balances.

Amino Acids↗
PubMed1988

Differential distribution of D and L amino acids between the 2' and 3' positions of the AMP residue at the 3' terminus of transfer ribonucleic acid.

Amino acids esterified to the ribose group of 5'-adenylic acid (AMP) constantly migrate between the 2' and 3' positions of the ribose at a rate of several times per second, which is slower than the rate of peptide-bond synthesis (15-20 per sec). Because the contemporary protein-synthesizing system only incorporates amino acids into protein when they are at the 3' position of the AMP at the terminus of tRNA, the value of the equilibrium constant relative to the 2' and 3' positions is of considerable interest. Differences between D and L isomers in this regard might be especially revealing. We have used N-acetylaminoacyl esters of AMP as models for the 3' terminus of tRNA and find that glycine and the L amino acids consistently distribute predominantly to the 3' position (approximately equal to 67% 3', approximately equal to 33% 2'), but D amino acids distribute to that position generally to a lesser extent and in a manner inversely related to the hydrophobicity of the amino acid side chain. This consistency of the L amino acid preference for the 3' position, combined with the inconsistency of the D amino acid preference, may be one reason for the origin of our contemporary protein-synthesizing system, which forms the peptide bond preferentially with L amino acids and only when they are in the 3' position of the ribose moiety of the AMP residue at the 3' terminus of every tRNA.

Adenosine Monophosphate↗
PubMed1998

Bidirectional modulation of insulin action by amino acids.

Amino acids have been shown to stimulate protein synthesis, inhibit proteolysis, and decrease whole-body and forearm glucose disposal. Using cultured hepatoma and myotube cells, we demonstrate that amino acids act as novel signaling elements in insulin target tissues. Exposure of cells to high physiologic concentrations of amino acids activates intermediates important in the initiation of protein synthesis, including p70 S6 kinase and PHAS-I, in synergy with insulin. This stimulatory effect is largely due to branched chain amino acids, particularly leucine, and can be reproduced by its transamination product, ketoisocaproic acid. Concurrently, amino acids inhibit early steps in insulin action critical for glucose transport and inhibition of gluconeogenesis, including decreased insulin-stimulated tyrosine phosphorylation of IRS-1 and IRS-2, decreased binding of grb 2 and the p85 subunit of phosphatidylinositol 3-kinase to IRS-1 and IRS-2, and a marked inhibition of insulin-stimulated phosphatidylinositol 3-kinase. Taken together, these data support the hypothesis that amino acids act as specific positive signals for maintenance of protein stores, while inhibiting other actions of insulin at multiple levels. This bidirectional modulation of insulin action indicates crosstalk between hormonal and nutritional signals and demonstrates a novel mechanism by which nutritional factors contribute to insulin resistance.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Renal, cardiovascular and endocrine responses of fetal sheep at 0.8 of gestation to an infusion of amino acids.

Amino acid infusions increase renal blood flow (RBF) and glomerular filtration rate (GFR) and stimulate tubular reabsorption in adults. To characterize the effects of amino acids on fetal renal haemodynamics, tubular sodium reabsorption, acid-base homeostasis and plasma renin levels, 11 chronically catheterized fetal sheep aged 121 +/- 1 days (term ~150 days) were infused I.V. for 4 h with alanine, glycine, proline and serine (0.1, 0.1, 0.06 and 0.06 mmol min(-1), respectively) in 0.15 M saline at 0.165 ml min(-1). Eight control fetuses were given saline. During amino acid infusion, plasma amino acid levels increased up to 20-fold (P < 0.005). GFR increased by 50 +/- 8 % (P < 0.001); there was only a small transient increase in RBF. Proximal fractional sodium reabsorption fell from 74.6 +/- 2.9 to 55.5 +/- 5.4 % (P < 0.005). Distal sodium delivery increased, but a smaller percentage of this distal sodium load was reabsorbed (P < 0.005). Thus fractional sodium reabsorption fell from 95.5 +/- 0.9 to 81.4 +/- 2.0 % (P < 0.005). There was a large diuresis, natriuresis, kaliuresis and increase in osmolar excretion (P < 0.005). Plasma sodium and chloride concentrations fell (P < 0.005). Plasma osmolality did not change. Plasma renin levels fell (P < 0.05), cortisol levels increased (P < 0.05), and there was a compensated metabolic acidosis. Thus the fetal sheep kidney demonstrated a remarkable functional capacity to respond to amino acid infusion. The increase in filtration fraction and the lack of an increase in RBF suggest that efferent arteriolar vasoconstriction occurred, a very different response from the renal vasodilatation seen in adult animals.

Acid-Base Equilibrium↗
PubMed1997

Ascorbic acid and amino acid values in the aqueous humor of a patient with Lowe's syndrome.

BACKGROUND: Aminoaciduria is found in Lowe's syndrome. No studies of concentrations of ascorbic acid and amino acids in the aqueous humor of the syndrome have been performed. We examined these concentrations in a patient with Lowe's syndrome. METHODS: Ascorbic acid and amino acid levels in the aqueous humor and plasma of a male infant were measured by means of high-performance liquid chromatography. The patient, who had congenital cataract, miotic pupils, opaque corneas, glaucoma, aminoaciduria, normal levels of ascorbic acid and amino acid in the plasma, and renal tubular acidosis, underwent trabeculotomy, lensectomy, and anterior vitrectomy in both eyes. RESULTS: Intraocular pressure in both eyes decreased to within the normal range, but both corneas remained opaque. The amino acid levels in the aqueous humor were similar to those in the plasma, but intracameral ascorbic acid levels were decreased. After topical instillation of ascorbic acid, the corneas became transparent. The proband's mother had good visual acuity but paracentral lens opacities in both eyes. His maternal grandmother had scattered cortical opacities in both lenses. CONCLUSION: In this infant with Lowe's syndrome, we found intracameral levels of amino acids similar to those in the plasma. Levels of ascorbic acid in the aqueous humor were decreased.

Adolescent↗
PubMed1987

High-performance liquid chromatographic determination of enantiomeric amino acids and amino alcohols after derivatization with o-phthaldialdehyde and various chiral mercaptans. Application to peptide hydrolysates.

o-Phthaldialdehyde in combination with a chiral mercaptan is a powerful chiral reagent for the pre-column derivatization of many enantiomeric compounds bearing primary amino groups. The diastereoisomers formed can efficiently be resolved on conventional reversed-phase columns. Simultaneous determination of the enantiomers of various amino acids, amino alcohols and biogenic amines was achieved by gradient elution and fluorescence detection. The resolution was optimized by varying the chiral mercaptan in the reagent, Boc-L-cysteine, N-acetyl-L-cysteine and N-acetyl-D-penicillamine being used for this purpose. The resolutions were calculated. Most of the enantiomers showed good resolution with each of the three chiral mercaptans, whereas some enantiomers were only separable by one or two of them. The method was applied to the analysis of peptide hydrolysates. The composition of peptides bearing L- and D-amino acids and an amino alcohol was determined.

Amino Acids↗
PubMed1991

Transduction mechanisms for the taste of amino acids.

Amino acids are important taste stimuli for a variety of animals. One animal model, the channel catfish, I. punctatus, possesses sensitive taste receptor systems for several amino acids. Neurophysiological and biochemical receptor binding studies suggest the presence of at least three receptor pathways: one is a relatively nonspecific site(s) responsive to short-chain neutral amino acids such as L-alanine (L-ALA); another is responsive to the basic amino acid L-arginine (L-ARG); still another is a low affinity site for L-proline (L-PRO). Several possible transduction pathways are available in the taste system of this animal model for these amino acids. One of these, formation of inositol trisphosphate (IP3) and cyclic AMP (cAMP), is mediated by GTP-binding regulatory proteins, while another involves ion channels directly activated by stimuli. L-ALA is a potent stimulus to cAMP and IP3 accumulation, while L-ARG at low concentrations is without effect. On the other hand, L-ARG and L-PRO, but not L-ALA, are able to activate stimulus-specific and cation-selective channels in taste epithelial membranes reconstituted in phospholipid bilayers at the tips of patch pipettes. Preliminary studies using mouse taste tissue demonstrate that monosodium-L-glutamate (MSG) did not enhance production of IP3 or cAMP. However, in reconstitution experiments using taste epithelium of mouse, conductance changes due to MSG are observed. The specificity of this channel(s) and its uniqueness have yet to be determined.

Amino Acids↗