Lysine biologically-available

Unmodified lysine is, in principle, biologically available and will be determined as such by animal assays (21) and enzymatic methods (22, 23,24), or determined as reactive lysine by the Carpenter method (23,24,25, 26) and by guanidina-tion (24, 27). 

Lysine present as a SchifFs base or aldosylamine is biologically available as demonstrated with synthetic free SchifFs bases (c-benzylidenelysine and c-salicylidenelysine) (9,28) (see Table I). This can be explained by the reversibility of the reaction with the subsequent regeneration of lysine, probably in the acid medium of the stomach. 

The Amadori derivative of lysine and glucose (c-deoxyfruc-tosyllysine) is not biologically available to rats (9,28). The same has been observed also with the other Amadori compounds of lysine (a- and a-c-di-derivatives) and those Amadori compounds derived from other amino acids such as methionine (29), tryptophan (12,30,32), and leucine (12). 

For the untreated (3H-lysine) casein, the radioactive urinary and fecal excretions were low, about 10% and 4%, respectively, after 74 h. The unexcreted radiactivity was retained in the organism and incorporated into the proteins. The radioactivity measured in the liver, muscle, and kidneys (expressed as percentage of the ingested dose per gram of tissue) can be considered as a function of the quantity of lysine incorporated into the protein of these tissues and proportional to the biological availability of 3H-lysine in the casein samples. The value of radioactivity measured in the liver, muscle, and kidneys can be considered as being given by a protein whose lysine is 100% available (see Table III, Column 5). 

For the advanced Maillard (3H-lysine) casein, the urinary excretion was low and the fecal excretion high, suggesting that lysine engaged in advanced Maillard products is absorbed at a very low extent by the intestine and that the intestinal microflora does not metabolize these products. The radioactivity measured in the liver and in the muscle indicates that the biological availability of lysine in the advanced Maillard (3H-lysine)-casein is lower than that determined by the chemical analysis (reactive lysine). About 50% of reactive lysine should be not biologically available (see Table III, Columns 4 and 5). The level... 

Biological Availability of the Free Isopeptides. The biological availability of free c-(y-glutamyl)lysine was tested first by Mauron (118), who found that this isopeptide s growth-promoting effect was as good as that of free lysine. This result was confirmed later by Waibel and Carpenter (81) and Finot et al. (83) (see Table I). In contrast, free c-(/ -aspartyl) lysine was not found to be biologically available (83) (see Table I). 

We therefore can conclude easily that protein-bound e-(/ -aspartyl)-lysine is not biologically available, but the question that arises is whether protein-bound c-(y-glutamyl) lysine is biologically available. If it is, what is the biological mechanism involved in the release of lysine from this isopeptide, free and protein-bound ... 

Friedman, M., and Gumbmann, M. R. (1979). Biological availability of epsilon-N-methyl-L-lysine, 1-N-methyl-L-histidine, and 3-N-methyl-L-histidine in mice. Nutrition Reports International,... 

We heated an albumin mix with 1 % formaldehyde for 2 h at 80 °C (Table 4) and found that lysine digestibility and protein digestibility for chicks were reduced to 75 % and 72 % of their original values and that chemically reactive lysine as measured by fluorodinitrobenzene (FDNB) was 76% of its original value. Biologically available lysine... 

The classic bioassay procedure which measures the animal growth response as a function of graded amounts of the missing nutrient in an otherwise complete diet and using the slope-ratio technique for evaluation is theoretically the soundest method for determining the biological availability of essential nutrients such as vitamins and indispensable amino acids. Lysine and methionine are the two amino acids for which detailed bioassay procedures have been... 

Biosensors are also available for glucose, lactate, alcohol, sucrose, galactose, uric acid, alpha amylase, choline, and L-lysine. All are amperometric sensors based on O2 consumption or H2O2 production in conjunction with the turnover of an enzyme in the presence of substrate. In the case of glucose oxidase reaction, the normal biological reaction is ... 

The initial Schiff base is digestible but after the Amadori rearrangement, the products are not metabolically available. Since lysine is the amino acid most likely to be involved and is an essential amino acid, Maillard browning reduces the biological value of proteins. Interaction of lysine with lactose renders the adjacent peptide bond resistant to hydrolysis by trypsin, thereby reducing the digestibility of the protein. 

In each of these formulas additional free OH groups are available on the silicon so that it is possible to crosslink more than two polysaccharide chains. Silicon may function as a biological crosslinking agent in connective tissue. Silaffins, small polypeptides containing polyamine side chains of modified lysine residues, apparently initiate silica formation from silicic acid in diatoms.0... 

Tt is well recognized that the nutritional value of dietary proteins de-pends primarily on the content of their constituent amino acids, especially of their essential amino acids. Because of deficiencies of lysine and methionine, and to a lesser extent of a few other amino acids, proteins from plants and other alternative sources have low biological quality. Moreover, incomplete digestion of the protein also may result in a lack of complete availability (I) of the essential amino acids and may further reduce its value. In many raw plant foodstuffs such as soybeans, common beans, or unprocessed protein foods, undenatured... 

Proteins react with polyphenols such as phenolic acids, flavonoids, and tannins, which occur widely in plant products. These reactions may result in the lowering of available lysine, protein digestibility, and biological value (Hurrell 1984). 

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