Riboflavin nomenclature

The answer is e. (Murray, pp 627-661. Sciiver, pp 3897-3964. Sack, pp 121-138. Wilson, pp 287-320.) Ascorbic acid (vitamin C) is found in fresh fruits and vegetables. Deficiency of ascorbic acid produces scurvy, the sailor s disease. Ascorbic acid is necessary for the hydroxylation of proline to hydroxyproline in collagen, a process required in the formation and maintenance of connective tissue. The failure of mesenchymal cells to form collagen causes the skeletal, dental, and connective tissue deterioration seen in scurvy. Thiamine, niacin, cobalamin, and pantothenic acid can all be obtained from fish or meat products. The nomenclature of vitamins began by classifying fat-soluble vitamins as A (followed by subsequent letters of the alphabet such as D, E, and K) and water-soluble vitamins as B. Components of the B vitamin fraction were then given subscripts, e.g., thiamine (Bi), riboflavin (B2), niacin [nicotinic acid (B3)], panthothenic acid (B5), pyridoxine (Bg), and cobalamin (B ). The water-soluble vitamins C, biotin, and folic acid do not follow the B nomenclature. 

Subsequent to the identification of 3,4-dihydroxy-2-butanone 4-phosphate (8) as the 4-carbon precursor of 6,7-dimethyl-8-ribityllumazine in the late 1980s,it was not difficult to show that the j3 subunits catalyzed the condensation of 6 with 8 under formation of the lumazine derivative 9. The heavy riboflavin synthase can now be correctly addressed as a riboflavin synthase/lumazine synthase complex. However, the designation /3 subunit of riboflavin synthase clung tenaciously to the 16 kDa peptide that had ultimately been assigned a function as lumazine synthase (reaction VIII in Figure 1) notably, this somewhat unfortunate nomenclature survives in databases, despite the fact that in most organisms, lumazine synthase and riboflavin synthase (reaction IX in Figure 1) are separate proteins. 

The active component of the old yellow enzyme is riboflavin 5 -phosphate, usually called flavin mononucleotide and abbreviated FMN. This nomenclature is somewhat incorrect again, since we do not have a nucleotide, i.e. an N-glycoside of a ribose phosphate. In spite of this, the name and abbreviation have been adopted, and actually the close similarity to real nucleotides must be conceded. 

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