Amino-Nitrogen

AMINO-NITROGEN, the nitrogen of the NH₂ group attached to a carbon atom that is bonded either to hydrogen atoms or to another carbon atom. In the animal organism, amino-nitrogen is found, mainly, in the form of amino acids and amines. In proteins and peptides, the linkage of amino acids to one another is effected through amino-nitrogen; this linkage is broken during acid and alkaline hydrolysis and under the influence of proteases (see). The amino-nitrogen of protein digestion products enters the blood from the small intestine in the form of amino acids, and from the large intestine in the form of amines, which are formed there from amino acids under the influence of microbes. The entry of amino acids into the bloodstream occurs very slowly, so that the amount of amino-nitrogen in the blood never reaches significant levels. According to many authors, the amount of blood amino-nitrogen drops during passage through the liver, which apparently depends on the deaminating activity of the latter, converting amino-nitrogen into urea nitrogen. Principles of determining amino-nitrogen: 1. According to Sörensen—free alkaline-reacting amino groups are bound by formaldehyde, after which an equivalent amount of acidic (carboxyl) groups can be titrated with alkali. 2. According to van Slyke—decomposition of amino groups by nitrous acid with the release of free nitrogen and gasometric determination of the latter. 3. According to Folin—colorimetrically, by a color reaction with β-sulfonaphthoquinone. These methods provide relative figures suitable for comparative determinations, but the absolute value of the results obtained is not very reliable. According to Folin, 100 cubic centimeters of blood contains 4–8 mg of amino-nitrogen. Studies by Bang, who investigated the change in the amino-nitrogen fraction of the blood under various physiological and pathological conditions and arrived at the following results, give a value of the same order of magnitude: 1. Amino-nitrogen is distributed between plasma and erythrocytes in favor of the latter [due to the adsorption of amino-nitrogen-containing products by blood corpuscles (Zbarsky)]. 2. The amount of amino-nitrogen does not change during fasting or during intensive feeding. This, however, is doubtful, as indicated by the works of London and others. 3. Upon the introduction of amino acids into the intestine or bloodstream, an increase in blood amino-nitrogen is observed; accordingly, significant amounts of amino-nitrogen are excreted in the urine. At the same time, the content of amino-nitrogen increases in the tissues, where it is deposited from the blood. In cases where amino-nitrogen was not excreted in the urine, the animal died (apparently due to acid poisoning). 4. In experimental nephritis (sublimate, chromium salts), the amount of blood amino-nitrogen remains constant. 5. In experimental phosphorus poisoning, a sharp increase in blood amino-nitrogen occurs, which can be explained either as a result of the impairment of the deaminating activity of the liver or as a result of the autolysis of the latter. An increase in amino-nitrogen was also observed by other authors in certain cases of liver disease. Bang's data can be considered only as preliminary, in view of the inaccuracy of the methodology used. Amino-nitrogen is also found under normal conditions in lymph and other tissues; it is constantly encountered in urine, where it can be determined by one of the methods described above.