Flavins INDEX

Glutathione reductase is especially sensitive to riboflavin depletion, in deficient animals, the activity of glutathione reductase responds earlier and more markedly than any other index of riboflavin stams apart from liver concentrations of flavin coenzymes and the activity of hepatic flavokinase (Prentice and Bates, 1981a, 1981b). The activity of the enzyme in erythrocytes can therefore be used as an index of riboflavin status. 

Spectroscopic techniques are popular as a means of detection on chips. Examples include the determination of flavins and DNA by fluorescence. Spectrophotometric techniques are often used for biological samples . Mass spectrometry has also been used. Benetton et al. coupled electrospray ionisation MS to a chip while Sillon et al. developed a low cost mass spectrometer which incorporated the ionisation chamber, filter and detector on the chip. A fibre optic coupler has been developed as a detector. The dual optical fibre configuration (one transmitting, one receiving, (Eigure 10.5)) in the chip forms the microchannel as well as the detector itself and measures refractive index changes but can also be used to measure absorbance . 

Ethyl-9-(i -D-ribityl)isoalloxazine (6-ethylflavin), is a low potency antagonist of riboflavin in the nutrition of the rat with an inhibition index of approximately 400. It has been found to possess about 3% of the activity of riboflavin when used as the sole flavin in the nutrition of L. casei ... 

Diethyl-9-(i -D-ribityI)isoalloxazine (diethylriboflavm), is a competitive antagonist of riboflavin for growth in the rat with an inhibition index of about 6. When any but very small quantities are administered to the riboflavin-deficient rat, a growth response is obtained . The compound does not, however, serve as a replacement of riboflavin in the nutrition of the animal because it does not permit survival - . It can serve as the sole source of flavin in the nutrition of L. casei for which organism it has 100% of the activity of equivalent amounts of riboflavin up to the concentration of 8.22 lO moles per ml. At higher concentrations its activity levels off at about 90%. It is also able to serve as the sole source of flavin for B. lactis acidi. ... 

The compound is a potent, reversible antagonist of riboflavin in the nutrition of L. casei with an inhibition index of 76. When L. casei ATCC 7469 is incubated for several days in a medium containing a mixture of this flavin and a small amount of riboflavin a modified form of L. casei emerges. This modified form is able to utilize either riboflavin or the b-chloro-y-methyl-flavin as its sole flavin - . 

Contents L. MINALE, G. CIMINO, S. DE STEFANO, and G. SODANO, Natural Products from Porifera - R. M. COATES, Biogenetic-Type Rearrangements of Terpenes - K. L RINEHART, JR., and L. S. SHIELD, Chemistry of the Ansamycin Antibiotics - A. FONTANA and C. TONIOLO, The Chemistry of Tryptophan in Peptides and Proteins -P. HEMMERICH, The Present Status of Flavin and Flavocoenzyme Chemistry - Author Index - Subject Index. 

Oxidized glutathione (GSSG) is reduced back to active GSH by glutathione reductase, which uses NADPH as the reducing agent. Glutathione reductase is a flavin-dependent enzyme, and its activity, or its activation after incubation with FAD, can be used as an index of vitamin status (section 11.7.4.1), in the same way as activation of transketolase by thiamin diphosphate can be used as an index of thiamin status (section 11.6.4.1). 

Urine. The sensitive determination of riboflavin excreted into urine is of interest because it seems to be a good means for monitoring dietary intake of the vitamin. The flavin content in urine can establish the vitamin B2 status of an individual and it can be used as an index of the relative bioavailability of vitamin... 

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