Amino acids combined

Some proteins may be very large, indeed. Titin, for example, a muscle protein and the largest known protein, includes in its molecule over 26,000 combined amino acid units. 

Simply on the basis of the normal composition of marine organisms, we would expect proteins and peptides to be normal constituents of the dissolved organic carbon in seawater. While free amino acids might be expected as products of enzymic hydrolysis of proteins, the rapid uptake of these compounds by bacteria would lead us to expect that free amino acids would normally constitute a minor part of the dissolved organic pool. This is precisely what we do find the concentration of free amino acids seldom exceeds 150 xg/l in the open ocean. It would be expected that the concentration of combined amino acids would be many times as great. There have been relatively few measurements of proteins and peptides, and most of the measurements were obtained by measuring the free amino acids before and after a hydrolysis step. Representative methods of this type have been described [245-259]. Since these methods are basically free amino acid methods, they will be discussed next in conjunction with those methods. 

A fluorescence method that would measure either free or combined amino acids, depending upon the pH of the solution, was originally proposed by Udenfriend et al. [282] and adapted for seawater by North [283] and Packard and Dortch [284], In this Fluran method, peptides normally yield maximum fluorescence by pH 7, while amino acids fluoresce best at pH 9. With the proper choice of buffers, the fluorescence of peptides and proteins can be differentiated from that due to free amino acids. 

In the third decade of this century, as the methods for detection and identification of single amino acids were improved, the number of observations showing the existence of these compounds in mine increased. Systematic investigations on this problem were, however, still lacking. The only exception was the studies of Kapeller-Adler et al. (FI, Kl, K2, K3), who demonstrated the existence of histidine in normal urine and found the correlation between the concentration of this amino acid and the different phases of pregnancy. Up to 1940 the problem of free and combined amino acids in mine was in fact passed over. 

The simplest methods are usually restricted to the estimation of the amount of combined amino acids as a whole or of some definite fraction thereof separated from urine in certain fixed conditions. More efficient separation procedures permit identification of some simple peptides, which represent in many cases the nonphysiological constituents of abnormal urine. 

Introduction of microbiological methods for the determination of amino acids made possible the estimation of the amount of both free and combined amino acids in urine. Dunn et al. (D4), Thompson and Kirby (Tl), Eckhard and Davidson (El), and Woodson et al. (W3) estimated the amount of amino acids liberated in the course of acid or, as in the case of tryptophan determination, alkaline hydrolysis. Microbiological and colorimetric methods used for the determination of certain amino acids present very little opportunity for evaluating the proper quantitative relations between free and combined amino acids, since under the applied condition both combined and free amino acids are equally involved in the reaction. In 1949 Albanese et al. (A3) applied such methods to the quantitative determination of free and combined amino acids in the nondiffusible fraction of urine, and subjected the procedures to broad criticism from just this point of view. 

The development of modem methods, suitable for the analysis of ampholytes in biological fluids, provided means for isolating from urine some chemically better defined fractions containing peptide compounds. The methods used did not, however, exclude the existence of some other forms of combined amino acids in the fractions studied. 

A similar ion-exchange resin method was used by Ling in 1955 (LI) for the examination of combined amino acids in urine. According to this procedure urine was desalted and simultaneously freed from amino acids by using Amberlite IR-112, H+-form resin. The effluent collected from the column was then fractionated on Amberlite IRA, OH--form resin, by successive elution with 0.16 N acetic acid, 0.08 N formic acid, 0.25 N formic acid, 0.08 N hydrochloric acid, and finally with 0.16 N formic acid. The solutions of all acids contained 10% of acetone. The collected fractions were hydrolyzed with hydrochloric acid and the liberated amino acids identified by means of paper chromatography. 

Goes, J. I., N. Handa, S. Taguchi, T. Hama, and H. Saito. 1995. Impact of UV radiation on the production patterns and composition of dissolved free and combined amino acids in marine phytoplankton. Journal of Plankton Research 17 1337-1362. 

Coffin, R B. 1989. Bacterial uptake of dissolved free and combined amino acids in estuarine waters. Limnology and Oceanography 34 531-542. 

Jorgensen, N. O. G., N. Kroer, R. B. Coffin, X.-H. Yang, and C. Lee. 1993. Dissolved free amino acids, combined amino acids, and DNA as sources of carbon and nitrogen to marine bacteria. Marine Ecology Progress Series 98 135—148. 

Middleboe, M., N. H. Borch, and D. L. Kirchman. 1995b. Bacterial utilization of dissolved free amino acids, dissolved combined amino acids and ammonium in the Delaware Bay estuary Effects of carbon and nitrogen limitation. Marine Ecology Progress Series 128 109-120. 

Keil, R. G., and D. L. Kirchman. 1993. Dissolved combined amino acids Chemical form and utilization by marine bacteria. Limnology and Oceanography 38 1256—1270. 

DFAA, dissolved free amino acids DCAA, dissolved combined amino acids TDCHO, total dissolved combined carbohydrates DPA, dissolved primary amines. 

Combined Amino Acids. This expression refers to a group of sub-... 

In the case of adult subjects, the most suitable expression seems unquestionably to be one indicating the amounts (in mg) per 24-hr collection, both for free and for combined amino acids. When relative amounts are of interest, it is of course preferable to compute the amounts on a molar basis (S24). For the sake of possible comparison with other data than one s own, it is always highly desirable to indicate at the same time, total nitrogen output, 24-hr urine volume, body weight, and, if possible, body height. 

Comparison with values from the literature obtained by microbiological methods has been discussed by Stein (S32). The main objection to microbiological methods lies in the fact that amino acid derivatives or combined amino acids may be as readily available to the microorganisms used in these methods as are the parent amino acids from which they... 

Figure 8.5 Experimental fluxes of NELt-1-, NO3U dissolved organic nitrogen (DON), urea, dissolved free amino acids (DFAA), and dissolved combined amino acids (DCAA) across the sediment-water interface in cores collected in Hog Island Bay (USA). (Modified from Tyler et al., 2003.)...

The decay of proteins and amino acids in phytoplankton cultures, under oxic and anoxic conditions, indicated very little selectivity (Nguyen and Harvey, 1997). However, 15 to 95% of the total particulate amino acid pool consisted of polypeptides/proteins in anoxic treatments versus 8 to 65% in oxic conditions. The similarity of particulate amino acid composition during phytoplankton decay agrees with other work in the Delaware Bay estuary (USA), which showed similar composition in the dissolved combined amino acid (DCAA) pool (Keil and Kirchman, 1993). 

Figure 9.35 Cycling of particulate and dissolved [both free and combined amino acids (DFAA and DCAA)] in porewaters which are considered to be intermediates of biotic and abiotic processing. (Modified from Burdige and Martens, 1988.)...

Allochthonous DON sources from terrestrial runoff, plant detritus leaching, soil leaching, sediments, and atmospheric deposition may also represent important inputs to estuaries (Berman and Bronk, 2003). DON typically represents about 60 to 69% of the TDN in rivers and estuaries (Berman and Bronk, 2003). The major components of DON include urea, dissolved combined amino acids (DCAA), DFAA, proteins, nucleic acids, amino sugars, and humic substances (Berman and Bronk, 2003). However, less than 20% of DON is chemically characterized. 

Keil, R., and Kirchman, D. (1991b) Dissolved combined amino acids in marine waters as determined by vapor-phase hydrolysis method. Mar. Chem. 33, 243-259. 

Five species of common edible crabs were used. They were cooked in boiling water containing 3% NaCl for 20 minutes according to commercial practice. After cooling, the leg meat was removed from the crabs of both sexes and extracted with hot water. The extracts were then deproteinized with 80% ethanol and analyzed for free and combined amino acids, nucleotides and related compounds, quaternary ammonium bases, sugars, organic acids, and inorganic ions. 

Methionine Sulfoxide and Other Combined Amino Acids in the German Cockroach... 

Alkaline hydrolysis of cockroach residues subsequent to extraction under nitrogen with 80% ethanol yielded methionine and methionine sulfoxide in a ratio of 10 to 1. Additional evidence for the presence of combined methionine sulfoxide was obtained by measuring the amount of methionine sulfoxide-S35 in acid and enzymatic hydrolyzates after assimilation of Na2S3504. The data are believed to be indicative of naturally occurring peptide- or polysaccharide -bound methionine sulfoxide. Other combined amino acids were determined by ion exchange chromatography of the 5% trichloroacetic acid-insoluble cockroach residues after hydrolysis with acid or alkali. /3-Alanine, normally present only in the soluble fraction of an organism, was found in the insoluble, proteinaceous residue. 

Other Combined Amino Acids. The data from two chromatographic analyses on chromobead resin and one on Amberlite IR-120 were averaged to give the data shown in Table V. The tryptophan value is from a... 

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