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PubMed1984

Relation of riboflavin nutriture in healthy elderly to intake of calcium and vitamin supplements: evidence against riboflavin supplementation.

The status of riboflavin nutriture was evaluated in 24 healthy elderly female residents of a private, nonprofit facility for the care of ambulatory elderly. Riboflavin intake by history was greater than or equal to the recommended dietary allowances (RDA) for this nutrient in all but three subjects, and the average intake in the group as a whole was 50% greater than the RDA. Confirmatory of the findings by history, the status of riboflavin nutriture was excellent in nearly all subjects as evaluated by urinary riboflavin excretion and erythrocyte glutathione reductase activity coefficient. By contrast, calcium intake was greater than or equal to the RDA in ony four of the 24 subjects. The adequacy of calcium intake was found to depend upon a sufficiently high percentage of the total dietary intake of riboflavin being derived from milk and dairy products. It was observed that individual calcium intakes were less than 80% of the RDA unless 40% or more of the total intake of riboflavin was derived from milk and dairy products rather than from other food sources. In those subjects taking daily supplementation with a single multivitamin tablet containing low levels of riboflavin, the total intake of riboflavin and its urinary excretion were increased similarly, suggesting that even small amounts of riboflavin are not retained by elderly subjects consuming a diet adequate in riboflavin.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Specificity of riboflavin molecular groups for riboflavin binding to rat small intestinal brush border membrane.

The binding of riboflavin to rat small intestinal brush border membrane at equilibrium was formerly shown to have a saturable, specific component, prevailing at the intraluminal physiological concentrations of the vitamin. In this study, the specificity of riboflavin binding to rat small intestinal brush border vesicles was further investigated using structural analogues of riboflavin. The vesicles, prepared by Ca(2+)-precipitation, were incubated at 25 degrees C, for 20 min, in the presence of [3H]-riboflavin at physiological intraluminal concentrations for rat, and each analogue, at appropriate concentrations. Three groups of analogues were used, that were derived from the riboflavin molecule by modifying one of the following positions: the ribityl side chain, position 3, and position 8 of the isoalloxazine moiety. Group specificity was assessed by determining the inhibition potency of each analogue on the saturable component of riboflavin binding to the vesicles. Inhibition constants were calculated, according to Dixon, for lumiflavin, lumichrome, and for analogues substituted at position 8. Specific riboflavin binding was inhibited competitively by most of the analogues used. Substitutions at the ribityl side chain or at position 3 of the isoalloxazine moiety reduced the inhibition power. Substitutions at position 8 enhanced the inhibition power in direct proportion to the bulk of the substituents. We conclude that the ribityl side-chain and the NH group at position 3 are essential for recognition by the specific binding sites, whereas the methyl group at position 8 is important but not essential. The analogues that bind to specific membrane sites for riboflavin share specificity requirements with many riboflavin binding proteins, and are also good substrates for the intracellular phosphorylating enzyme flavokinase. Thus, the riboflavin-binding component in the membrane is likely to be a protein with high specificity. Cellular internalization of the membrane bound vitamin is probably achieved by phosphorylation of the vitamin bound to the inner side of the membrane.

Animals↗
PubMed1975

[Riboflavin and lumiflavin analogs and alloxazine derivatives. I. Effect on riboflavin synthesis by and growth of Bacillus subtilis].

Effect of riboflavin, lumiflavin and a number of alloxazine derivatives is studied on the growth of three Bacillus subtilis strains with different genetic state of riboflavin operon as well as their ability to show coenzyme and regulating properties characteristic of vitamin B2. The fission of the ribityl chain of the riboflavin molecule results in the complete loss of both coenzyme and regulating properties of vitamin B2 (analogues of lumiflavin and alloxazine derivatives). Different types of esterification of hydroxyl groups of ribityl chain or its replacement by dulcityl chain results in the decrease of regulating properties characteristic of riboflavin as an end product of biosynthetic pathway (tetraacetylriboflavin and its derivatives, tetrapropionyl- and tetrabutyrylriboflavin) or to the loss of coenzyme and regulating activities (galactoflavin and tetrabenzoylriboflavin). The length increase of hydrocarbon chain under esterification of hydroxyl groups in ribityl chain results in enhancing vitamin B2 non-specific inhibitory effect on the growth of Bacillus subtilis strains studied. The replacement of 8-CH3 group in the riboflavin molecule by amino- or D-ribitylaminogroup results in the formation of specific antimetabolites, 8-amino(nor)riboflavin and 8-D-ribitylamino(nor)riboflavin respectively. Depending on the nature of other alterations or replacements of the 8-CH3 group of riboflavin molecule and their combinations with alterations of ribityl chain the reduction of the regulating activity (8-alpha-bromtetraacetylriboflavin) or a sharp decrease of coenzyme and regulating functions (analogues N 9 to N 15) takes place. The replacement of riboflavin-5-N-oxide and 2-thioriboflavin type did not affect the studied properties of riboflavin.

Bacillus subtilis↗
PubMed1977

Utilization of analogues of riboflavin by the riboflavin-deficient chick embryo.

Detailed studies of the biological activity of several analogues of riboflavin in the riboflavin-deficient chick embryo were undertaken to extend our knowledge of the comparative biochemistry of these flavins. The riboflavin-deficient eggs were produced by hens homozygous for an autosomal recessive gene (rdrd). 7-Ethyl-8-methyl-flavin was found to be an adequate replacement for riboflavin in che chick embryo, a finding which mimics its effect in the riboflavin-deficient rat. 7,8-Diethyl-flavin was found to be an antagonist in the chick embryo as had been found to be true in the rat. 7-Methyl-8-ethyl-flavin can not be used as a replacement for riboflavin in the chick embryo and further, it inhibits the utilization of riboflavin in normal eggs. 7-Methyl-8-ethyl-flavin had been found to be an adequate replacement for riboflavin in the riboflavin-deficient rat. The classes mammalia and aves are clearly different in respect to the utilization of this flavin.

Animals↗
PubMed1990

Urinary riboflavin excretion after a load test in rural China as a measure of possible riboflavin deficiency.

Urinary excretion of riboflavin was measured in 3318 adults 4 h after an oral dose of riboflavin. Male and female subjects aged 35-64 years were selected from 65 mostly rural counties located in 24 provinces of China. Counties were selected to represent a range of seven of the most prevalent cancer mortality rates in China and within counties households were selected at random. Urinary riboflavin excretion levels after a load test, erythrocyte glutathione reductase activity coefficients (EGR-AC), dietary riboflavin intakes, and a large number of other biochemical, dietary, and environmental parameters were measured. Mean dietary intake of riboflavin was 75 per cent of the Chinese recommended dietary allowances (CRDA). Mean meat intake per reference man was very low (26.4 +/- 23.7 g/d) in comparison to Western standards and milk was not consumed at all in most counties. Mean EGR activity coefficients measured on 'blood pools' for both males (1.47 +/- 0.14) and females (1.48 +/- 0.16) indicated that more than two-thirds of the population surveyed was in the medium or high risk category of riboflavin deficiency. Using current reference standards of less than 1.4 mg for 4-h urinary excretion of riboflavin after a 5 mg load, more than 70 per cent of the individuals examined exhibited low levels usually associated with high risk of riboflavin deficiency. In view of the lack of specificity for clinical indications of riboflavin deficiency and the tentative validity of the present CRDA, the interpretation of the data is problematic. We suggest that the present CRDA for this vitamin is set too high and requires critical review and possibly some revision.

Administration, Oral↗
PubMed1999

Riboflavin and riboflavin-derived cofactors in adolescent girls with anorexia nervosa.

BACKGROUND: Thyroid hormones, riboflavin, riboflavin cofactors, and organic acids were assessed in girls with anorexia nervosa. OBJECTIVE: The objective was to examine the effect of malnutrition and low thyroid hormone concentrations on erythrocyte and plasma riboflavin metabolism and their relation with urinary organic acid excretion. DESIGN: Seventeen adolescent girls with anorexia nervosa [body mass index (BMI; in kg/m2): 14.8 +/- 2.2] and 17 age-matched, healthy girls (control subjects; BMI: 20.5 +/- 2.2) took part in the feeding study. Erythrocyte and plasma riboflavin as well as riboflavin cofactors (flavin mononucleotide and flavin adenine dinucleotide) were assessed by HPLC, whereas urinary organic acids were assessed by gas chromatography-mass spectrometry. RESULTS: Anorectic patients who began a feeding program had higher erythrocyte riboflavin (3.5 +/- 2.2 compared with <0.1 nmol/mol hemoglobin; P < 0.001), lower plasma flavin adenine dinucleotide (57.8 +/- 18.5 compared with 78.5 +/- 54.3 nmol/L; P < 0.05), and higher urinary ethylmalonic acid (7.12 +/- 4.39 compared with 1.3 +/- 2.8 micromol/mmol creatinine; P < 0.001) and isovalerylglycine (7.65 +/- 4.78 compared with 3.8 +/- 0.9 micromol/mmol creatinine; P < 0.05) concentrations than did control subjects. Triiodothyronine concentrations were low and negatively correlated with plasma riboflavin concentrations (r = -0.69, P < 0.01). Not all patients showed improvements in these biochemical indexes after 30 d of refeeding. CONCLUSIONS: The low triiodothyronine concentrations observed in anorexia nervosa could alter the extent of riboflavin conversion into cofactors, thus leading to high erythrocyte riboflavin concentrations, low plasma flavin adenine dinucleotide concentrations, and high rates of ethylmalonic acid and isovalerylglycine excretion.

Absorptiometry, Photon↗
PubMed1997

Biosynthesis of riboflavin: an unusual riboflavin synthase of Methanobacterium thermoautotrophicum.

Riboflavin synthase was purified by a factor of about 1,500 from cell extract of Methanobacterium thermoautotrophicum. The enzyme had a specific activity of about 2,700 nmol mg(-1) h(-1) at 65 degrees C, which is relatively low compared to those of riboflavin synthases of eubacteria and yeast. Amino acid sequences obtained after proteolytic cleavage had no similarity with known riboflavin synthases. The gene coding for riboflavin synthase (designated ribC) was subsequently cloned by marker rescue with a ribC mutant of Escherichia coli. The ribC gene of M. thermoautotrophicum specifies a protein of 153 amino acid residues. The predicted amino acid sequence agrees with the information gleaned from Edman degradation of the isolated protein and shows 67% identity with the sequence predicted for the unannotated reading frame MJ1184 of Methanococcus jannaschii. The ribC gene is adjacent to a cluster of four genes with similarity to the genes cbiMNQO of Salmonella typhimurium, which form part of the cob operon (this operon contains most of the genes involved in the biosynthesis of vitamin B12). The amino acid sequence predicted by the ribC gene of M. thermoautotrophicum shows no similarity whatsoever to the sequences of riboflavin synthases of eubacteria and yeast. Most notably, the M. thermoautotrophicum protein does not show the internal sequence homology characteristic of eubacterial and yeast riboflavin synthases. The protein of M. thermoautotrophicum can be expressed efficiently in a recombinant E. coli strain. The specific activity of the purified, recombinant protein is 1,900 nmol mg(-1) h(-1) at 65 degrees C. In contrast to riboflavin synthases from eubacteria and fungi, the methanobacterial enzyme has an absolute requirement for magnesium ions. The 5' phosphate of 6,7-dimethyl-8-ribityllumazine does not act as a substrate. The findings suggest that riboflavin synthase has evolved independently in eubacteria and methanobacteria.

Amino Acid Sequence↗
PubMed1977

Enhanced riboflavin incorporation into flavins in newborn riboflavin-deficient rats.

The incorporation of a subcutaneous injection of [14C]riboflavin (2.5 muCi/100 g body wt) into flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and flavins bound covalently to proteins was determined at 1, 6, and 18 h in liver, cerebrum, and cerebellum from progeny of normal and maternally riboflavin-deficient Holtzman rats. Radioactivity remaining as riboflavin was also determined under these circumstances. Experiments were initiated within 24 h of birth. In both groups of newborn rats, the incorporation of radioactive riboflavin into covalently bound flavins in liver and brain proceeded more slowly than into the other flavin fractions. In addition, radioactivity incorporated into covalently bound flavins comprised a relatively smaller proportion of the total amount incorporated in brain than in liver. In progeny of riboflavin-deficient dams, an increased rate of incorporation of riboflavin into all three flavin derivatives, particularly FAD, was observed in liver and brain, compared to results in normal progeny. These data provide evidence that maternal riboflavin deficiency enhances the incorporation of riboflavin into tissue flavins in liver, cerebrum, and cerebellum from newborn rats.

Animals↗
PubMed2005

Deactivation of triplet-excited riboflavin by purine derivatives: important role of uric acid in light-induced oxidation of milk sensitized by riboflavin.

The reactivity of purine derivatives (uric acid, xanthine, hypoxanthine, and purine) toward triplet-excited riboflavin in aqueous solution at pH 6.4 is described on the basis of kinetic (laser flash photolysis), electrochemical (square-wave voltammetry), and theoretical data (density functional theory, DFT). Direct deactivation of triplet-excited riboflavin in aqueous solution, pH 6.4 at 24 degrees C, in the presence of uric acid, xanthine, and hypoxanthine strongly suggests a direct electron transfer from the purine to the triplet-excited riboflavin with k = 2.9 x 10(9) M(-1) s(-1) (DeltaH(++) = 14.7 kJ mol(-1), DeltaS(++) = -15.6 J mol(-1) K(-1)), 1.2 x 10(9) M(-1) s(-1) (DeltaH(++) = 34.3 kJ mol(-1), DeltaS(++) = +45.3 J mol(-1) K(-1)), and 1.7 x10(8) M(-1) s(-1) (DeltaH(++) = 122 kJ mol(-1), DeltaS(++) = +319 J mol(-1) K(-1)), respectively. From the respective one-electron oxidation potentials collected in aqueous solution at pH 6.4 for uric acid (E = +0.686 vs normal hydrogen electrode, NHE), xanthine (E = +1.106 vs NHE), and hypoxanthine (E = +1.654 vs NHE), the overall free energy changes for electron transfer from the quencher to the triplet-excited riboflavin are as follows: uric acid (DeltaG(o) = -114 kJ mol(-1)), xanthine (DeltaG(o) = -73.5 kJ mol(-1)), hypoxanthine (DeltaG(o) = -20.6 kJ mol(-1)), and purine (DeltaG(o) > 0). The inertness observed for purine toward triplet-excited riboflavin corroborates with its electrochemical inactivity in the potential range from 0 up to 2 V vs NHE. These data are in agreement with the DFT results, which show that the energy of the purine highest occupied molecular orbital (HOMO) (-0.2685 arbitrary unit) is lower than the energy of the semioccupied molecular orbital (SOMO) (-0.2557 a.u.) of triplet-excited riboflavin, indicating an endergonic process for the electron-transfer process. The rate-determining step for deactivation by purine derivatives can be assigned to an electron transfer from the purine derivative to the SOMO orbital of the triplet-excited riboflavin. The results show that uric acid may compete with oxygen and other antioxidants to deactivate triplet-excited riboflavin in milk serum and other biological fluids leading to a free radical process.

Animals↗
PubMed1992

Estimation of the dietary riboflavin required to maximize tissue riboflavin concentration in juvenile shrimp (Penaeus monodon).

The riboflavin requirements of marine shrimp (Penaeus monodon) were evaluated in a 15-wk feeding trial. Juvenile shrimp (initial mean weight, 0.13 +/- 0.05 g) were fed purified diets containing seven levels (0, 8, 12, 16, 20, 40 and 80 mg/kg diet) of supplemental riboflavin. There were no significant differences in weight gains, feed efficiency ratios and survival of shrimp over the dietary riboflavin range. The riboflavin concentrations in shrimp bodies increased with the increasing vitamin supplementation. Hemolymph (blood) glutathione reductase activity coefficient was not a sensitive and specific indicator of riboflavin status of the shrimp. The dietary riboflavin level required for P. monodon was found to be 22.3 mg/kg diet, based on the broken-line model analysis of body riboflavin concentrations. Shrimp fed unsupplemented diet (riboflavin concentration of 0.48 mg/kg diet) for 15 wk showed signs of deficiency: light coloration, irritability, protuberant cuticle at intersomites and short-head dwarfism.

Animals↗
PubMed1993

Effects of riboflavin deficiency and riboflavin administration on carcinogen-DNA binding.

A study was conducted to assess the effects of riboflavin deficiency and riboflavin supplementation on carcinogen-DNA binding. After 12 wk on a riboflavin-sufficient or a riboflavin-deficient diet male Wistar rats were administered 3H-labelled benzo[a]pyrene (BP) ip. [3H]BP was given either at a uniform dose of 450 muCi/rat irrespective of body weight or at a dose adjusted to body weight. After 17 hr the animals were killed, various organs were dissected and the level of [3H]BP bound to DNA was quantified in organs that are known to be the seats of drug metabolism (i.e. the liver, lungs and intestinal mucosa). In a separate experiment, the effect of riboflavin supplementation on BP-DNA binding was also investigated. When [3H]BP was administered at 450 microCi/rat, BP-DNA binding was markedly increased in the livers and intestinal mucosae of the pair-fed and deficient groups compared with controls. With the administration of [3H]BP adjusted to body weight, no differences in BP-DNA binding between groups were observed in any tissue. However, on administration of riboflavin there was a decrease in the level of [3H]BP bound to DNA in almost all tissues, especially in the lungs, where the reduction was significant. The results suggest that undernutrition/riboflavin deficiency may increase the risk of carcinogenesis by way of an increase in carcinogen binding, which however can be reversed by riboflavin supplementation.

Animals↗
PubMed1985

Effect of riboflavin deficiency on reproductive performance and on biochemical indices of riboflavin status in the rat.

Young female rats were made riboflavin-deficient by feeding a purified diet containing casein (210 g/kg). This basal diet provided 0.40 mg riboflavin/kg diet, to which was added additional riboflavin at 0, 0.12 or 0.25 mg/kg diet. Control animals received the same diet with 15 mg added riboflavin/kg. The diets were given for 4 weeks before mating, then throughout pregnancy and for 15 d of lactation. With no added riboflavin in the diet, reproduction was severely impaired and fetal resorption was usually observed. With 0.12 mg added riboflavin/kg diet, however, reproduction was usually successful, and the growth of dams and pups was only marginally depressed in comparison with pair-fed controls optimally supplied with riboflavin. The activation coefficient (stimulated:basal activity) of erythrocyte glutathione reductase (NAD(P)H) (EC 1.6.4.2) was high, and the concentration of riboflavin in the liver was correspondingly low in the dams receiving diets containing 0.12 or 0.25 mg added riboflavin/kg and in their sucking pups at 15 d post partum. Riboflavin levels in the milk from both groups of dams were about eightfold lower than in controls. There was little evidence that the sucking pups could maintain their riboflavin level at the expense of that in the maternal tissues.

Animals↗
PubMed1990

Adriamycin-induced increase in serum aldosterone levels: effects in riboflavin-sufficient and riboflavin-deficient rats.

Previous studies in rats have demonstrated that 1) aldosterone enhances biosynthesis of renal flavin coenzymes; 2) riboflavin analogs inhibit the synthesis of aldosterone; and 3) adriamycin inhibits flavin coenzyme biosynthesis. In their entirety, these findings suggest that both diminished flavin coenzyme biosynthesis induced by adriamycin and a dietary riboflavin deficiency would result in decreased formation of aldosterone. The present study examined the effects of adriamycin treatment on serum aldosterone in rats consuming either a diet adequate in riboflavin or a riboflavin-deficient diet. Groups of rats fed specially prepared diets were injected for 3 days with adriamycin (cumulative dose range, 6-24 mg/kg BW). Pair-fed controls were given saline. After death, adrenal glands were excised, and blood samples were analyzed for aldosterone levels. No changes in adrenal weights or protein and potassium concentrations were observed after adriamycin treatment. In contrast to initial predictions, in riboflavin-sufficient rats, serum aldosterone levels were markedly enhanced by adriamycin in a dose-related manner. Riboflavin-deficient animals had lower basal aldosterone levels and markedly attenuated responses to adriamycin than did riboflavin-sufficient rats. In separate groups of adriamycin-treated rats fed a normal chow diet, serum aldosterone levels increased, and serum corticosterone levels showed a small but significant decline. In addition, adriamycin treatment caused an increase in urinary potassium excretion and a decrease in sodium excretion. These results suggest that flavins play a decisive role in regulating the levels of aldosterone and raise the possibility that the adriamycin-induced increase in serum aldosterone may be part of the pathogenetic mechanisms of cardiovascular toxicity and overall muscular weakness.

Aldosterone↗
PubMed2005

Evolution of vitamin B2 biosynthesis: riboflavin synthase of Arabidopsis thaliana and its inhibition by riboflavin.

A synthetic gene specifying the catalytic domain of the Arabidopsis thaliana riboflavin synthase was expressed with high efficiency in a recombinant Escherichia coli strain. The recombinant pseudomature protein was shown to convert 6,7-dimethyl-8-ribityllumazine into riboflavin at a rate of 0.027 s-1 at 25 degrees C. The protein sediments at a rate of 3.9 S. Sedimentation equilibrium analysis afforded a molecular mass of 67.5 kDa, indicating a homotrimeric structure, analogous to the riboflavin synthases of Eubacteria and fungi. The protein binds its product riboflavin with relatively high affinity (Kd =1.1 microM). Product inhibition results in a characteristic sigmoidal velocity versus substrate concentration relationship. Characterization of the enzyme/product complex by circular dichroism and UV absorbance spectroscopy revealed a shift of the absorption maxima of riboflavin from 370 and 445 to 399 and 465 nm, respectively. Complete or partial sequences for riboflavin synthase orthologs were analyzed from 11 plant species. In each case for which the complete plant gene sequence was available, the catalytic domain was preceded by a sequence of 1-72 amino acid residues believed to function as plastid targeting signals. Comparison of all available riboflavin synthase sequences indicates that hypothetical gene duplication conducive to the two-domain architecture occurred very early in evolution.

Amino Acid Sequence↗
PubMed1985

Riboflavin status of adolescent southern Chinese: riboflavin saturation studies.

Riboflavin saturation studies were done on 36 high-school boys in Canton whose mean daily intake of riboflavin was 0.45 mg and who showed clinical evidence of deficiency. The boys were given a 2 mg load of riboflavin orally followed by supplements of 0.5, 1.0 and 1.5 mg riboflavin to three groups; a control group received no supplement. After 14 days' supplementation, excretion of riboflavin had increased significantly in all supplemented groups, but not in the control group. The 4-h excretion of riboflavin after the 2 mg load averaged 8.6 per cent of the load for all groups before supplementation. After 14 days' supplementation it was significantly increased only in the groups receiving 1.0 and 1.5 mg daily. This suggests that tissue saturation may not be achieved until the background intake of 0.45 mg/d is increased by between a further 0.5-1.0 mg daily. After 17 days' supplementation with 1.0 and 1.5 mg riboflavin, scrotal dermatitis disappeared. However, even in the 0.5 mg supplemented group, eight out of ten boys with scrotal dermatitis had responded and a total intake of 0.95 mg/d may be enough to prevent clinical deficiency.

Adolescent↗
PubMed1995

Homogeneous assays for riboflavin mediated by the interaction between enzyme-biotin and avidin-riboflavin conjugates.

Homogeneous-type enzyme-linked competitive binding assays utilizing the synthetic enzyme-biotin and avidin-riboflavin conjugates are developed for the detection of riboflavin as well as its binder protein. The activity of the enzyme-biotin conjugate is inhibited in the presence of the avidin-riboflavin conjugate, and the observed inhibition is reversed in an amount dependent on the concentration of riboflavin binding protein (RBP) added. Upon additions of free riboflavin to the mixture, activity is reinhibited in an amount proportional to the riboflavin concentration. Three different enzymes are examined as the labels: glucose-6-phosphate dehydrogenase, adenosine deaminase, and alkaline phosphatase. The catalytic activity of these enzymes, when conjugated with biotin, is shown to be inhibited to a significant degree (> 90%) by the binding of the avidin-riboflavin conjugate, and reversed upon additions of RBP.

Adenosine Deaminase↗
PubMed1990

Riboflavin deficiency in cultured rat hepatoma cells: a model for studying the hepatic effects of riboflavin deficiency.

The acyl-CoA dehydrogenases are a family of mitochondrial flavoenzymes required for fatty acid beta-oxidation and branched-chain amino acid degradation. The hepatic activity of these enzymes, particularly the short-chain acyl-coenzyme A (CoA) dehydrogenase, is markedly decreased in riboflavin deficient rats. We now report that the in vivo effects of riboflavin deficiency on the beta-oxidation enzymes of this group are reproduced in FAO rat hepatoma cells cultured in riboflavin-deficient medium. Although it has been long known that hepatic short-chain acyl-CoA dehydrogenase activity is the most severely affected of the straight-chain specific enzymes in riboflavin deficiency, the mechanism by which its activity is decreased has not been reported. We have used this new cell culture system to characterize further this mechanism. Whole cell extracts from riboflavin-deficient and control cells were subjected to analysis by denaturing polyacrylamide gel electrophoresis. The contents of the gels were then electroblotted onto nitrocellulose filters and probed with short-chain acyl-CoA dehydrogenase-specific antiserum. The relative abundance of enzyme antigen was estimated autoradiographically. Our findings indicate that short-chain acyl-CoA dehydrogenase activity changes in parallel with its antigen, suggesting that riboflavin deprivation does not affect the activity of individual enzyme molecules. Further, no evidence of extramitochondrial enzyme precursor was found on the blots, making unlikely a significant block in the mitochondrial uptake process. These findings suggest that changes in short-chain acyl-CoA dehydrogenase activity in riboflavin deficiency result from either increased synthesis or decreased degradation of the enzyme.

Acyl-CoA Dehydrogenase↗