Amino acids in tissues

Li, P., Kim, S. W., Datta, S., Pond, W. G., and Wu, G. (2008). Dietary supplementation with cholesterol and docosahexanoic acid affects concentrations of amino acids in tissues of young pigs. Nitric Oxide 19, 259-265. 

Boyd, T.A., Cha, C.-J., Forster, R.P. and Goldstein, L. (1977). Free amino acids in tissues of the skate Raja erinacea and the sting ray Dasyatis sabina effects of environmental dilution. Journal of Experimental Zoology 199,435-442. 

Karentz, D., Dunlap, W. C., and Bosch, I., Temporal and spatial occurrence of UV-absorbing mycosporine-like amino acids in tissues of the Antarctic sea urchin Sterechinus neumayeri during springtime ozone depletion, Mar. Biol., 129, 343, 1997. 

Adriaenssens et al. (A3) have described a simple screening method for the study of amino acids in tissues using frozen slices. Efron (ElO) has described methods for the extraction of free amino acids from urine, plasma, spinal fluid, sweat, and cellular material. Saifer (SI) has made a comparative study of seven published procedures for extracting free amino acids from brain tissue and concluded that perchloric acid extraction is the simplest and gives the most consistent results.With minor modifications this extraction method can be applied to amniotic fluid (S5), brain and other tissues (All, SI), plasma, urine, cerebrospinal fluid, etc. 

A3. Adriaenssens, K., Vanheule, R., Kareher, D., and Mardens, Y., A simple screening method for the study of amino acids in tissues using frozen slices. Clin. Chim. Acta 18, 351-354 (1967). 

Tryptophan is one of 20 to 22 amino acids that are required for the synthesis of protein within tissues. Tryptophan is assumed to consist of 1.5% of the total amino acids in tissue protein. Assuming that the adult male at nitrogen equilibrium synthesizes approximately 225 to 250 g of protein daily (approximately 3 g/kg/d), then approximately 3.5 g of tryptophan is utilized daily for protein synthesis. This is of special interest because there is no net accretion of body protein at nitrogen balance. Thus, a large flux of amino acids, including tryptophan, participates in this pathway daily. Actually, the tryptophan... 

Table 5.5 values for transport of neutral amino acids in tissues... 

Amino acids are small and highly mobile molecules, thus them efficient fixation in tissues is an essential prerequisite for their subsequent immunocytochemical detection. The main fixatives that can be used for immobilizing amino acids in tissues are glutaraldehyde, carbodiimide, and formaldehyde (formaldehyde is referred to here as paraformaldehyde, to distinguish it from formalin). Glutaraldehyde has traditionally been the fixative of choice for retaining amino acids in tissues prior to their immunocytochemical detection. Unfortunately, glutaraldehyde is incompatible with immunofluorescence-... 

This procedure has become more and more important owing to the occurrence of D-enantiomers of amino acids in tissues of various organisms. In addition, amino acid residues in dietary proteins have been reported to have been significantly racemized. 

Sulfoxides occur widely in small concentrations in plant and animal tissues, eg, aHyl vinyl sulfoxide [81898-53-5] in garlic oil and 2,2 -sulfinylbisethanol [3085-45-8] as fatty esters in the adrenal cortex (1,2). Homologous methyl sulfinyl alkyl isothiocyanates, which are represented by the formula CH3SO(CH2) NCS, where n = 3 [37791-20-1], 4 [4478-93-7], 5 [646-23-1], 8 [75272-81-0], 9 [39036-83-4], or 10 [39036-84-5], have been isolated from a number of mustard oils in which they occur as glucosides (3). Two methylsulfinyl amino acids have also been reported methionine sulfoxide [454-41-1] from cockroaches and the sulfoxide of i -methylcysteine, 3-(methylsulfinyl)alaiiine [4740-94-7]. The latter is the dominant sulfur-containing amino acid in turnips and may account in part for their characteristic odor (4). 

Pyrazol-1 -ylalanine, an isomer of histidine, was isolated from Citrullus vulgaris (watermelon) seed and its structure was confirmed by comparison with synthetic material 107). It was the major free amino acid in the dormant dry seed but was present in only trace amounts in vegetative tissue. While present in seed extracts of other members of the Cucurbitaceae, it has not been identified as occurring in members of other plant families. 

Molecules that contain an equal number of ionizable groups of opposite charge and that therefore bear no net charge are termed zwitterions. Amino acids in blood and most tissues thus should be represented as in A, below. 

These initial findings do not exclude other possible formaldehyde-induced reactions with tissue proteins. Notably, this first model system was not designed to detect the role of lysine residues. Lysine has a propensity to react with and form a variety of different types of cross-links with other amino acids in the presence of formaldehyde.1,3 417 Therefore, it is likely to also be important in reactions with formaldehyde. In fact, peptides with internal lysine residues were purposefully excluded from this initial study for technical reasons. To explore the importance of lysine residues in antigen retrieval, an alternative method was employed. 

The modification of amino acids in proteins and peptides by oxidative processes plays a major role in the development of disease and in aging (Halliwell and Gutteridge, 1989, 1990 Kim et al., 1985 Tabor and Richardson, 1987 Stadtman, 1992). Tissue damage through free radical oxidation is known to cause various cancers, neurological degenerative conditions, pulmonary problems, inflammation, cardiovascular disease, and a host of other problems. Oxidation of protein structures can alter activity, inhibit normal protein interactions, modify amino acid side chains, cleave peptide bonds, and even cause crosslinks to form between proteins. 

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