Biological Chemistry - Berezov, T. T., Korovkin, B. F. 1998

Vitamins
Water-Soluble Vitamins
Vitamin PP

Vitamin PP (nicotinic acid, nicotinamide, niacin) is also known as the antipellagric vitamin (from Italian preventive pellagra), since its deficiency causes a disease known as pellagra.

Nicotinic acid has been known for a long time; however, it was not until 1937 that C. Elvehjem isolated it from Liver extract and demonstrated that administration of nicotinic acid (or its amide, nicotinamide) or liver preparations prevents The Development of pellagra or cures it. In 1904, A. Harden and W. Young established that The conversion of glucose to ethanol in a Cell-free Yeast extract requires the presence of an easily dialyzable cofactor called cozymase. The chemical composition of a similar cofactor from mammalian erythrocytes was elucidated in 1934 by O. Warburg and W. Christian, and it proved to be a derivative of nicotinic acid amide.

Nicotinic acid is a pyridine compound containing a carboxyl group (nicotinamide differs by having an amide group).

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Vitamin PP is sparingly soluble in Water (approximately 1%), but readily soluble in aqueous alkali solutions. Nicotinic acid crystallizes as white needles.

The most characteristic signs of vitamin PP deficiency, i.e., pellagra (from Italian pelle agra meaning rough Skin), are skin lesions (dermatitis), Disorders of the digestive tract (diarrhea), and Nervous system dysfunction (dementia).

Dermatitis is most often symmetrical and affects areas of the skin exposed to direct sunlight: the backs of the hands, neck, and face; the skin becomes red, then brown, and rough. Intestinal lesions manifest as anorexia, nausea, abdominal pain, and diarrhea. Diarrhea leads to dehydration. The mucous membrane of the Large Intestine first becomes inflamed and then ulcerated. Specific to pellagra are stomatitis, gingivitis, and Tongue lesions accompanied by Swelling and fissures. Brain lesions manifest as headaches, dizziness, irritability, depression, and other symptoms including psychoses, psychoneuroses, hallucinations, etc. The symptoms of pellagra are particularly pronounced in patients with inadequate protein intake. This has been shown to be due to a deficiency of Tryptophan, which is a precursor of nicotinamide—partially synthesized in Human and Animal Tissues—as well as a deficiency of several other Vitamins (pyridoxine; see Chapter 12).

Biological role. Vitamin PP is a component of NAD and NADP, which serve as Coenzymes for A large number of dehydrogenases acting reversibly in redox reactions (the formulas of the coenzymes are given in Chapter 9).

It has been shown that A number of dehydrogenases use exclusively NAD or NADP (malate dehydrogenase and glucose-6-phosphate dehydrogenase, respectively), whereas others can catalyze Redox reactions in the presence of either of them (e.g., Glutamate dehydrogenase; see Chapter 12). In The process of Biological Oxidation, NAD and NADP act as intermediate carriers of electrons and protons between the oxidized substrate and flavin Enzymes (the MOLECULAR MECHANISMS OF participation of pyridine NUCLEOTIDES in this process are discussed in detail in Chapter 9).

Natural occurrence and daily requirement. Nicotinic acid is another vitamin widely distributed in PLANT AND ANIMAL organisms. For humans, the Main sources of nicotinic acid and its amide are rice, bread, potatoes, meat, liver, Kidneys, carrots, and other foods. The daily requirement for an adult is 18 mg.