Serum riboflavin

Riboflavin-binding protein <2 99 0 0.2 36 Serum riboflavin-binding protein... 

Riboflavin (vitamin B2 6.18) consists of an isoalloxazine ring linked to an alcohol derived from ribose. The ribose side chain of riboflavin can be modified by the formation of a phosphoester (forming flavin mononucleotide, FMN, 6.19). FMN can be joined to adenine monophosphate to form flavin adenine dinucleotide (FAD, 6.20). FMN and FAD act as co-enzymes by accepting or donating two hydrogen atoms and thus are involved in redox reactions. Flavoprotein enzymes are involved in many metabolic pathways. Riboflavin is a yellow-green fluorescent compound and, in addition to its role as a vitamin, it is responsible for the colour of milk serum (Chapter 11). 

Korycka-Dahl, M., Richardson, T. 1978. Photogeneration of superoxide anion in serum of bovine milk and in model systems containaing riboflavin and amino acids. J. Dairy Sci. 61, 400 107. 

Urinary excretions of nicotinic acid metabolites and 2-pyridone, as well as of 4-pyridoxic and xanthurenic acids were determined in 15 South African Bantu pellagrins before and after tryptophan administration (P13). Red blood cell riboflavine levels and serum glutamic-oxalacetic transaminase levels were also measured. The authors discussed the apparent inability of the pellagra patients to convert tryptophan to nicotinic acid as indicated by their low excretion of nicotinic acid metabolites before and after tryptophan load. The possibility that the subjects were also suffering from a riboflavine deficiency was also discussed. 

Riboflavin is absorbed by the gut and enters the bloodstream, where close to half of it is loosely bound to serum albumin. The main site of absorption is the ileum. As might be expected, when large doses (20- 60 mg) of riboflavin are eaten, much of the dose is promptly excreted in the urine (Zempleni et ai, 1996). The FAD CO factors based on riboflavin are called flavins enzymes using flavins as a cofactor are called flavopioteins. 

The reference interval for eiythrocyte riboflavin using a fluorometric method is 10 to 50jig/dL (266 to 1330nmol/L). The reference interval for serum or plasma levels of riboflavin is 4 to 24 Lig/dL (106 to 638 nmol/L). Guidance reference intervals for the activation coefficient of erythrocyte glutathione reductase by FAD are 1.20 (adequacy), 1.21 to 1.40 (marginal deficiency), and 1.41 and above (deficiency)... 

Riboflavin. Although not as extensively investigated as the transferrin and folate pathways, it was recently shown by Low and coworkers (91) that serum albumin coupled to riboflavin showed RME-mediated uptake in distal lung epithelium. In this paper-study the authors speculate that a similar uptake process exists in the small intestine. 

Fig 1. Effect of incubation meditun and excess hormone on L-T and L-T/, uptake by mouse neuroblastoma cells (NBATA3) After 45 min preincubation confluent cells were incubated at 37°C for 2 h with 10 pM labeled thyroid hormone in the absence or presence of lOpM unlabeled hormone. Wells measuring 28.2 cm contained 4 ml of culture medium (RPMI 1640) or Hank s balanced salt solution. After washing with phosphate buffered saline +0.1% serum albumin, the cells were harvested and their radioactivity measured. Mean SEM of 3 experiments performed in duplicate. Experiments were performed under diminished light to avoid spontaneous deiodination especially of T, in RPMI due to riboflavin and folic acid. 

Vitamin K3 (pharmaceutical preparations) chloramphenicol (pharmaceutical preparations) lactate (serum and pharmaceutical preparations) citrate (pharmaceutical preparations) riboflavine and riboflavine 5 -phosphate (pharmaceutical preparations) DNA (rabbit tissues) glucose (serum and urine)... 

The flavins in plasma may be bound to the plasma proteins albumins and immunoglobulins. During the examination of mechanisms of riboflavin uptake it was also found that serum albumin acts as a nonspecific transporter for riboflavin (Wangensteen et al. 1996). 

Wangensteen, O.D., Bartlett, M.M., James, J.K., Yang, Z.F., and Low, P.S., 1996. Low riboflavin nhanced transport of serum albumin across the distal pulmonary epithelium. Pharmaceutical Research. 13 1861-1864. 

A nonchromatographic method for the sensitive determination of riboflavin in human plasma and urine by enzyme-linked ligand-sorbent assay (ELLSA) was recently described (35). Using standard microtiter plate formate, a conjugate of flavin with bovine serum albumin is immobilized on a plastic surface. The RF... 

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