N

Nicotinamide

Tryptophan

FIGURE 13-17 Structures of niacin (nicotinic acid) and its derivative nicotinamide. The biosynthetic precursor of these compounds is tryptophan. In the laboratory, nicotinic acid was first produced by oxidation of the natural product nicotine—thus the name. Both nicotinic acid and nicotinamide cure pellagra, but nicotine (from cigarettes or elsewhere) has no curative activity.

reduced, and whose caloric needs are often met with distilled spirits that are virtually devoid of vitamins, including niacin. In a few places, including the Deccan Plateau in India, pellagra still occurs, especially among the poor. ■

Flavin Nucleotides Are Tightly Bound in Flavoproteins

Flavoproteins (Table 13-9) are enzymes that catalyze oxidation-reduction reactions using either flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD) as coenzyme (Fig. 13-18). These coenzymes, the flavin nucleotides, are derived from the vitamin ri-boflavin. The fused ring structure of flavin nucleotides (the isoalloxazine ring) undergoes reversible reduction, accepting either one or two electrons in the form of one or two hydrogen atoms (each atom an electron plus a proton) from a reduced substrate. The fully reduced forms are abbreviated FADH2 and FMNH2. When a fully oxidized flavin nucleotide accepts only one electron (one hydrogen atom), the semiquinone form of the isoal-

Frank Strong, 1908-1993

D. Wayne Woolley, 1914-1966

TABLE 13-9 Some Enzymes (Flavoproteins)

That Employ Flavin Nucleotide Coenzymes

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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