Biotin

The term "biotin" should now replace several old names, to wit: coenzyme R, protective factor X, the protective factor against egg white injury, the vitamin H and a part of the Bios II b or the adsorbable factor of the yeast growth promoting substance. It was isolated and from the Bios II b factor of yeast as a methyl ester of the empirical composition C 11 H 18 O 3 N 2 S and having a melting point of 166°-167° when highly purified. Saponification with cold alkali gives free biotin of the empirical composition C 10 H 16 O 3 N 2 S and melting at 230°-232°. Biotin is a simple monocarboxylic acid, a derivative of valeric acid. The nitrogen atoms form a urea structure which can be opened up with a loss of one carbon to form a diaminocarboxylic acid, from which in turn one can reform biotin by reaction with phosgene. The sulfur is functioning in a thioether structure, since a sulfone can be formed by oxidation. The most probable structure is that of 2′-keto-3,4-imidazolido-2-tetrahydrothiophene-n-valeric acid.

Looked upon as an active principle of yeast growth biotin is active even at a concentration of one part in 500,000,000,000. As the active substance stimulating several species of the root-nodule bacterium Rhizobium and obtained from concentrated cultures of Azotobacter, and previously known as coenzyme R (R=respiration) it shows effects in concentration of I part in 100 billion. As Vitamin H (H for "Haut" or skin) it counteracts the effects of avidin of both raw and dried egg white to the extent of 10,000 units per milligram by a rat assay method (i.e. 0.1 gamma of biotin per rat per day for 30 days protects against egg-white injury).

The biotin may be extracted from liver, dried eggs, potato starch, fresh eggs, dried yeast, autolyzed yeast.Inactivation of biotin has been accomplished both under acid and alkaline conditions. Aeration is not effective but stronger oxidizing agents destroy activity quickly and completely. Nitrous acid inactivates without a loss of nitrogen.Biological effects of biotin other than those used in assay of the foregoing effects concern the fatty infiltration of the livers of rats on a low fat diet with high biotin. The fermentation of yeast is increased as well as its respiration and growth both aerobically and anaerobically, in the presence of plentiful nitrogen in the form of ammonia. Butter-yellow tumor formation brought on by avidin-containing diets should be counteracted by biotin.

Methods for Determination of Amino Acids

In studies of protein digestion and of the nature and fate of the digestion products, methods for measuring the amounts of amino acids present in blood and other parts of the body are indispensable tools.

The first was the "nitrous acid method" which depends on the reaction: RCH(NH 2 )COOH+HNO 2 = RCH(OH)COOH+H 2 O+N 2 The N 2 gas is a measure of the amount of amino acid present. The reaction is not entirely specific for amino acids, because other amines with NH2 groups also react; but such amines are usually not present in important amounts or can be removed.

A later and more specific method depends on reaction with a mild oxidizing agent called ninhydrin. Its effect is indicated by the equation: RCH(NH 2 )COOH+O= RCHO+NH 3 +CO 2 The analysis consists merely of heating the mixture for a few minutes and measuring the CO 2 evolved. This reaction is so specific for free amino acids that it serves to pick out and measure them in the most diverse mixtures of other amines, organic acids, peptides and other biological products.