Niacin biologically active forms

In hmnan beings niacin is rapidly converted to its biologically active forms NAD, NADP, NADH, and NADPH. To test the validity of using niacin as our standard, we assayed the response of L. plantarum to those five forms in equimolar concentration (Figure 10). The diflFerence in the output was not statistically significant (p < 0.05), and we concluded that niacin was a valid indicator of the biologically active forms of this vitamin. 

The RMA have been shown to be simple, sensitive, and specific for the measurement of vitamin B12, folate, and niacin in the blood and for the measurement of vitamin B12 and folate in food. Further work will be carried out for the measurement of niacin in food. For the determination of the biologically active forms of niacin, the RMA is more specific than the TMA. The RMA is also more specific than the CPBA for the measurement of vitamin B12. The advantages of the RMA over the TMA are (i) it is sensitive and simple (ii) the colored or turbid materials do not interfere with the assay (iii) only small amounts of material are required and most important, (iv) RMA combines the biological specificity of the microorganisms with the precision of measuring radioactive decay as the endpoint. 

Figure 10. Comparison of biologically active forms of niacin in equimolar amounts. Shown are mean and 1 SD for three experiments each in duplicate. Biologically active forms were compared with nicotinic acidy and no difference was significant atp< 0.05 (19).

The biologically active form of niacin occurring in the tissues. 

Niacin is also known as vitamin PP or vitamin Bj. The term niacin describes two related compounds, nicotinic acid and nicotinamide (Figure 19.18), both with biological activity. Niacin is formed from the metabolism of tryptophan, and therefore it is not strictly a vitamin. It is a precursor of two cofactors nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential for the functioning of a wide range of enzymes involved in redox reactions. 

The term niacin refers to nicotinic acid (pyridine-3-carboxyhc acid), its amide nicotinamide, and derivatives that show the same biological activity as nicotinamide. A distinction between the two primary vitamin forms has to be considered, however, when considering some aspects of their metabolism and especially their different pharmacological actions at high doses. Structures of both vitamers and the two coenzyme forms containing the nicotinamide moiety are given in Figure 30-23. 

Vitamin B3 Vitamin B3 (niacin) has different physiologically active forms, nicotinic acid, nicotinamide, and their coenzymes, which are very stable at ambient temperature. Usually acid or alkaline hydrolysis are used to convert nicotinamide to nicotinic acid for quantitation of both vitamers as nicotinic acid the first treatment (acid) is used to quantitate biologically available niacin, while alkaline hydrolysis provides an estimate of the total niacin content. Nicotinic acid has been analyzed using ion exchange or RP chromatography with amino columns. Detection is performed with UV absorbance at 254 nm. 

The main dietary sources of nicotinamide are meat, fish, and egg yolks. During World War II, when the restrictions mainly involved these substances, the primary sources of vitamin PP were bread, tomatoes, spinach, and fruit. Some cereals—rice, wheat, bran, and corn—have a low biological activity with respect to niacin activity because these cereals contain niacin in the form of niacinogen. The vitamin is not freed by the gastric or intestinal juices and is therefore not... 

Both nicotinic acid and nicotinamide have been assayed by chemical and biological methods. Owing to the fact that niacin is found in many different forms in nature, it is important to indicate the specific analyte in question. For example, if biological assay procedures are used, it is necessary to indicate whether the analysis is to determine the quantity of nicotinic acid or if niacin activity is the desired result of the analysis. If nicotinic acid is desired, then a method specific for nicotinic acid should be used. If quantitation of niacin activity is the desired outcome, then all compounds (bound and unbound) which behave like niacin will assay biologically for this substance (1). 

Riboflavin in its coenzyme forms (FMN and FAD) plays key metabolic roles in biological oxidation-reduction reactions involving carbohydrates, amino acids and lipids, and in energy production via the respiratory chain. These coenzymes also act in cellular metabolism of other water-soluble vitamins through the production and activation of folate and pyridoxine (vitamin Bg) to their respective coenzyme forms and in the synthesis of niacin (vitamin B3) from tryptophan. In addition, some neurotransmitters and other amines require FAD for their metabolism. Recently, Chocano-Bedoya et al. (2011) suggested a possible benefit of high intakes of riboflavin (about 2.5 mg/ day) from food sources on the reduction of incidence of premenstrual syndrome. 

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