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PubMed1978

Plasma amino acid quantitation using gas chromatography chemical ionization mass spectrometry and 13C amino acids as internal standards.

A specific and sensitive method for the quantitation of 16 alpha amino acids has been developed. The technique employed uses methane chemical ionization gas chromatography mass spectrometry of the carboxy-n-butyl, N-trifluoroacetyl amino acid derivatives. A commercial 13C amino acid mixture provided individual internal standards for 14 alpha amino acids. A computer controlled quadrupole mass spectrometer was used for selected ion monitoring of those ions characteristic of each N-trifluoroacetyl amino acid/13C amino acid pair. A BASIC computer program located peak maxima and background intensities in each selected ion recording. Standard curves for each amino acid/13C amino acid pair were utilized by the program to calculate the plasma concentration of each detected amino acid. The total instrumental analysis occupied 30 min with sample preparation and derivatization accounting for an additional 2 h. Based on the detection of known amounts of standard amino acids the method will quantitate at the 1-5 nanogram level of detection.

Amino Acids↗
PubMed1995

Are proteins ideal mixtures of amino acids? Analysis of energy parameter sets.

Various existing derivations of the effective potentials of mean force for the two-body interactions between amino acid side chains in proteins are reviewed and compared to each other. The differences between different parameter sets can be traced to the reference state used to define the zero of energy. Depending on the reference state, the transfer free energy or other pseudo-one-body contributions can be present to various extents in two-body parameter sets. It is, however, possible to compare various derivations directly by concentrating on the "excess" energy-a term that describes the difference between a real protein and an ideal solution of amino acids. Furthermore, the number of protein structures available for analysis allows one to check the consistency of the derivation and the errors by comparing parameters derived from various subsets of the whole database. It is shown that pair interaction preferences are very consistent throughout the database. Independently derived parameter sets have correlation coefficients on the order of 0.8, with the mean difference between equivalent entries of 0.1 kT. Also, the low-quality (low resolution, little or no refinement) structures show similar regularities. There are, however, large differences between interaction parameters derived on the basis of crystallographic structures and structures obtained by the NMR refinement. The origin of the latter difference is not yet understood.

Amino Acid Sequence↗
PubMed1999

Analyzing mixtures of amino acids and carbohydrates using bi-modal integrated amperometric detection.

Described in this work is a new detection methodology - bi-modal integrated amperometric detection - for identifying peaks and as a tool for solving difficult separation problems. Bi-modal integrated amperometry makes it possible to selectively detect amino acids, amino sugars, and carbohydrates following their separation by anion-exchange. Selectivity is gained by two different methods of integrating anodic current on an otherwise identical waveform. As with the single-mode integrated amperometry reported previously, the limits of detection are in the femtomole range and linear calibration plots are possible over three orders of magnitude. This new detection method does not require analyte derivatization. The practical utility of this new technique is demonstrated in the analysis of amino acids and sugars in a recombinant mammalian cell culture medium.

Amino Acids↗
PubMed1975

Effects of D-, DL-and L-glutamic acid on chicks.

Studies were conducted to investigate the effects of D-, DL-, or L-glutamic acid on the chick. Supplementation of levels of L-glutamic acid to an amino acid mixture containing adequate levels of all the indispensable amino acids plus cystine and tyrosine resulted in increased growth up to 10% L-glutamic acid in the diet. Chicks tolerated as much as 15% L-glutamic acid with no growth retardation. Supplementation of D-glutamic acid at levels of 3.75 or 5% resulted in growth depressions of 18 and 38%, respectively, at the end of a 2-week experiment. Significant growth-depressing effects of these levels of D-glutamic acid and 7.5% of DL-glutamic acid were also observed with an amino acid diet as well as an isolated soybean protein diet. The growth-depressing effect was most severe during week 2 of the experiment. Additional vitamins and amino acid supplements failed to reverse the growth-depressing effect. Plasma glutamic acid concentration was not altered by the inclusion of D-glutamic acid in the diet, but generally, plasma free amino acid concentrations were increased. This was especially true of arginine. Free glutamic acid increased in the kidney and was lowered in the liver. Free ammonia was increased in both the liver and kidney when the D form was included in the diet. Implications of these findings are discussed.

Amino Acids↗
PubMed2004

Animal models of amino acid metabolism: a focus on the intestine.

One important advantage of animal models is that they permit invasive approaches and can be especially valuable when evaluating tissue and specific features of metabolism in situ. The focus of this presentation is current models, which are providing insights into the pivotal importance of the gastrointestinal tract in amino acid metabolism. Intestinal amino acid metabolism is conceptually and technically difficult to approach and multiple processes must be accounted for: protein synthesis and degradation; transit of amino acids in both directions across the basolateral surface of enterocytes, in addition to uptake on the apical side; arterio-portal differences as well as net portal appearance during uptake of defined amino acid mixtures appearing on the luminal side; first pass amino acid metabolism. These key features are largely impossible to study without access to invasive approaches in vivo and cannot be reproduced in vitro. Douglas Burrin, Ron Ball, and Vickie Baracos and their co-workers have used the domestic piglet to study intestinal protein metabolism in situ in three distinctly different and complementary approaches. Collectively, their approaches allow a means to describe the key elements of intestinal amino acid capture (and release) and the means to probe their physiological and pathological variation. It seems evident that the portal-drained viscera represent sites of quantitatively important amino acid catabolism, and that this capacity combined with hepatic metabolism would largely limit the possibility of toxic sequelae of amino acids taken orally.

Amino Acids↗
PubMed1999

Adverse effects of excess DL-methionine in calves with different body weights.

Adverse effects of excess methionine were examined using 12 Holstein bull calves trained to maintain reflex closure of the reticular groove even after weaning at 5 wk of age. Two nitrogen balance experiments were conducted for 2 wk each from 6 wk (Stage 1; BW = 62 kg) and 12 wk of age (Stage 2; BW = 103 kg) by dividing the calves into three groups at each stage. Calves were fed a corn-soybean meal diet at 62 g/kg of metabolic BW at both stages. At Stage 1, feed efficiency (gain:feed intake) and nitrogen retention did not differ between the group supplemented with .333 g of DL-methionine and .111 g of L-lysine monohydrochloride/kg BW per day and the group supplemented with isonitrogenous diammonium citrate, although the level of DL-methionine was considered to be enough to induce toxicity. Conversely, administration of isonitrogenous casein increased nitrogen retention. At Stage 2, administration of the same levels of methionine and lysine resulted in reduced feed intake, depressed nitrogen retention, and BW loss. Conversely, administration of the isonitrogenous casein did not increase nitrogen retention compared with the supplement of isonitrogenous diammonium citrate. Administration of excess methionine and lysine increased plasma methionine concentrations up to 230 (Stage 1) or 190 micromol/dL (Stage 2). Plasma lysine concentrations were less than 24 micromol/dL at every stage. Administration of the amino acid mixture decreased plasma concentrations of branched-chain amino acids and phenylalanine more obviously at Stage 2 than at Stage 1. These results indicated that abomasal administration of .333 g of DL-methionine/kg BW per day induced methionine toxicity at Stage 2 but methionine imbalance at Stage 1.

Animals↗