Riboflavin nutritional requirement

Horwitt, M. K. (1966) Nutritional requirements of man with special reference to riboflavin. Am. J. Clin. Nutr. 458-66. 

From a nutritional standpoint, it is significant that five of the B-complex vitamins (riboflavin, nicotinamide, thiamine, vitamin Be, and pantothenic acid) have been shown to be constituents of the coenzymes. The nutritional requirement of these vitamins is explained on the basis of their coenzyme function. In all cases the coenzyme form appears to be the sole bound form of the vitamin, and this then becomes the only metabolically active form for these particular vitamins. 

A more generous estimate of requirements, and the basis of reference intakes, is the intake at which there is normalization of the activity of the red cell enzyme glutathione reductase, a flavoprotein whose activity is especially sensitive to riboflavin nutritional status. Normal values of the activation coefficient (section 11.7.4.1) are seen in subjects whose habitual intake of riboflavin is between 1.2 and 1.5 mg/day. 

Recent studies of the exact nutritional requirements of various strains of hemol3 tic streptococci have resulted in their cultivation on media of completely defined chemical composition (232, 342, 449). Riboflavin has been included in the media in all cases, on the grounds of its known behavior as a growth factor for other bacteria, but it has not been shown always to be an essential component of the media. For the strains of hemolytic streptococci grown by Woolley and Hutchings (449) and by Schuman and Farrell (342), which included members of Lancefield s groups A, B, C, D, riboflavin was essential also for Streptococcus fecalis (342). Earlier work, before these media of defined composition had been worked out, had indicated the important part plaj ed by riboflavin in the nutrition of various strains of hemolytic streptococci (290,448). 

The combined dehydrogenation and decarboxylation of pyruvate to the acetyl group of acetyl-CoA (Fig. 16-2) requires the sequential action of three different enzymes and five different coenzymes or prosthetic groups—thiamine pyrophosphate (TPP), flavin adenine dinucleotide (FAD), coenzyme A (CoA, sometimes denoted CoA-SH, to emphasize the role of the —SH group), nicotinamide adenine dinucleotide (NAD), and lipoate. Four different vitamins required in human nutrition are vital components of this system thiamine (in TPP), riboflavin (in FAD), niacin (in NAD), and pantothenate (in CoA). We have already described the roles of FAD and NAD as electron carriers (Chapter 13), and we have encountered TPP as the coenzyme of pyruvate decarboxylase (see Fig. 14-13). 

Bates CJ (1987) Human requirements for riboflavin. American Journal of Clinical Nutrition 46, 122-3. 

Bates CJ (1987) Human riboflavin requirements, and metabolic consequences of deficiency in man and animals. World Review of Nutrition and Dietetics 50,215-65. 

McNulty H, McKinley MC, Wilson B, McPartlin J, Strain JJ, Weir DG, and Scott JM (2002) Impaired functioning ofthermolabile methylenetetrahydrofolate reductase is dependent on riboflavin status implications for riboflavin requirements. American Journal of Clinical Nutrition 76,436-41. 

A study for examining the feasibility of using stable iron isotopes to measure iron absorption by human subjects was carried out as part of a 12 week study of the effects of exercise on riboflavin requirements (20). The study was carried out in the Francis Johnson-Charlotte Young Human Nutrition Unit... 

It is still unknown how the pyrimidine intermediate 5 is dephosphorylated (reaction VI). However, it is well established that the dephosphorylation product 6 is condensed with 3,4-dihydroxy-2-butanone 4-phosphate (8) by the catalytic action of lumazine synthase (reaction VIII). The carbohydrate substrate 8 is in turn obtained from ribulose phosphate (7) by a complex reaction sequence that is catalyzed by a single enzyme, 3,4-dihydroxy-2-butanone 4-phosphate synthase (reaction VII). As mentioned above, the lumazine 9 is converted to riboflavin (10) by the catalytic action of riboflavin synthase (reaction IX). Ultimately, riboflavin is converted to the coenzymes, riboflavin 5 -phosphate (flavin mononucleotide (FMN), 11) and flavin adenine dinucleotide (FAD, 12) by the catalytic action of riboflavin kinase (reaction X) and FAD synthase (reaction XI). These reaction steps are required in all organisms, irrespective of their acquisition of riboflavin from nutritional sources or by endogenous biosynthesis. 

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