Conceptualization of functional single nucleotide polymorphisms of polycystic ovarian syndrome genes: an in silico approach.

PURPOSE: Polycystic ovarian syndrome (PCOS) is a multi-faceted endocrinopathy frequently observed in reproductive-aged females, causing infertility. Cumulative evidence revealed that genetic and epigenetic variations, along with environmental factors, were linked with PCOS. Deciphering the molecular pathways of PCOS is quite complicated due to the availability of limited molecular information. Hence, to explore the influence of genetic variations in PCOS, we mapped the GWAS genes and performed a computational analysis to identify the SNPs and their impact on the coding and non-coding sequences. METHODS: The causative genes of PCOS were searched using the GWAS catalog, and pathway analysis was performed using ClueGO. SNPs were extracted using an Ensembl genome browser, and missense variants were shortlisted. Further, the native and mutant forms of the deleterious SNPs were modeled using I-TASSER, Swiss-PdbViewer, and PyMOL. MirSNP, PolymiRTS, miRNASNP3, and SNP2TFBS, SNPInspector databases were used to find SNPs in the miRNA binding site and transcription factor binding site (TFBS), respectively. EnhancerDB and HaploReg were used to characterize enhancer SNPs. Linkage Disequilibrium (LD) analysis was performed using LDlink. RESULTS: 25 PCOS genes showed interaction with 18 pathways. 7 SNPs were predicted to be deleterious using different pathogenicity predictions. 4 SNPs were found in the miRNA target site, TFBS, and enhancer sites and were in LD with reported PCOS GWAS SNPs. CONCLUSION: Computational analysis of SNPs residing in PCOS genes may provide insight into complex molecular interactions among genes involved in PCOS pathophysiology. It may also aid in determining the causal variants and consequently contributing to predicting disease strategies.

Dental neglect and adverse birth outcomes: a validation and observational study.

OBJECTIVES: The objectives of this study were to validate the Indian translation of the Dental Neglect Scale (DNS) among a sample of parturient Indian women and to investigate dental neglect as a possible risk indicator in adverse birth outcomes. SUBJECTS AND METHODS: Three hundred and sixteen parturient women were administered the DNS and the Modified Dental Beliefs Scale (MDBS) and were also clinically examined for oral health status. Information regarding socio-economic status, weeks of gestation and birth weight was also collected. A gestation period of less than 37 weeks was considered as preterm and a birth weight of less than 2500 gm as 'low birth weight'. RESULTS: The Indian version of the DNS was found to be reliable (Cronbach's Alpha = 0.72) and valid for assessing dental neglect among the women. Factor analysis of the DNS revealed a two-factor structure accounting for 56% variance. Dental neglect was higher among those with poorer oral health status, lower socio-economic and educational status. Multinomial logistic regression showed high dental neglect and negative dental beliefs and not poor oral health, as significant risk indicators for occurrence of adverse birth outcomes. CONCLUSION: The finding of an association of adverse birth outcomes with dental neglect and beliefs, but not with poor oral health could be due to the influence of other more important general factors which had a direct bearing on birth outcomes. There is a need for further research to assess the role of behavioural factors like dental neglect as risk indicators for adverse birth outcomes.

Factors affecting oral health-related quality of life among pregnant women.

OBJECTIVES: To assess oral health status and to describe the possible factors that could affect the oral health-related quality of life (OHRQoL) among a group of pregnant rural women in South India. MATERIALS AND METHODS: A total of 259 pregnant women (mean age 26 +/- 5.5 years) who participated in the cross-sectional study were administered the Oral Health Impact Profile (OHIP-14) questionnaire and were clinically examined for caries and periodontal status. RESULTS: The highest oral impact on quality of life was reported for 'painful mouth' (mean: 1.7) and 'difficulty in eating' (mean: 1.1). On comparing the mean OHIP-14 scores against the various self-reported oral problems, it was seen that the mean OHIP-14 scores were significantly higher among those who reported various oral problems than those who did not. Those with previous history of pregnancies had more severe levels of gingivitis than those who were pregnant for the first time. Also gingival index scores, community periodontal index of treatment needs scores and previous pregnancies was associated with poorer OHRQoL scores. CONCLUSION: Increased health promotion interventions and simple educational preventive programmes on oral self-care and disease prevention during pregnancy can go a long way in improving oral health and lessening its impact on the quality of life in this important population.

HIV-protease inhibitors alter retinoic acid synthesis.

BACKGROUND: An increasing rate of highly-active antiretroviral therapy (HAART)-associated metabolic and morphological abnormalities has been reported in HIV-infected persons. Some of them resemble retinoid-related adverse events, indicating alteration(s) of retinol metabolism or of retinoic acid-mediated signalling. OBJECTIVE: To evaluate retinol levels in patients with or without HAART and to assess the effect of antiretroviral agents on retinal dehydrogenase (RALDH), a key enzyme involved in retinoic acid synthesis. DESIGN: Plasma retinol levels, measured in six patients receiving HAART and in five others with no antiretroviral therapy, were correlated with levels of serum retinol-binding proteins. We then studied the effects of seven antiretroviral agents on RALDH activity and gene expression in a kidney-derived cell line (LLCPK). RESULTS: Plasma retinol levels in patients receiving HAART were decreased in comparison with those not receiving antiretroviral drugs (51 +/- 5 versus 66 +/- 11 microg/dl; P = 0.03), whereas retinol-binding protein levels were increased (68 +/- 18 versus 45 +/- 10 mg/l; P = 0.04). RALDH activity was heightened by ritonavir (24%), indinavir (17%), saquinavir (17%), zalcitabine (14%), delavirdine (12%) and nelfinavir (10%) and decreased (22%) by DMP-450. RALDH gene expression was induced only by indinavir. CONCLUSIONS: These data indicate that certain retinoid-like adverse effects in HAART-receiving patients are not due to higher retinol levels. Enhanced RALDH activity or/and gene expression by some protease inhibitors could increase retinoic acid concentrations. Elevated retinoic acid levels might be responsible for retinoid-like or other adverse effects due to alterations in the expression of retinoic acid-responsive genes.

Localization of retinal dehydrogenase type 1 in the stomach and intestine.

Retinal dehydrogenase type 1 (RALDH1) is involved in the biosynthesis of retinoic acid (RA), a modulator of gene expression and cell differentiation. RALDH1 mRNA transcripts are present in the stomach and small intestine, and their expression is regulated by vitamin A status. In situ hybridization demonstrated RALDH1 mRNA expression in epithelial cells of the stomach, small intestine, and large intestine. Strong hybridization was also seen in the lamina propria of small intestinal mucosa and the smooth muscle layer of the small and large intestines. Immunocytochemical localization revealed RALDH1 staining in parietal cells of the stomach and prismatic cells of the small and large intestines. The presence of RALDH1 protein was also detectable within supportive glial cells around neuronal fibers throughout the muscular layers of the stomach as well as the small and large intestines. These data suggest an important role for RALDH1 in generating RA needed for the differentiation of specific epithelial cells in the stomach and intestines.

Kinetic properties of the human liver cytosolic aldehyde dehydrogenase for retinal isomers.

Retinoic acid exerts pleiotropic effects by acting through two families of nuclear receptors, RAR and RXR. All-trans and 9-cis retinoic acid bind RARs, whereas 9-cis retinoic acid binds and activates only the RXRs. To understand the role of human liver cytosolic aldehyde dehydrogenase (ALDH1) in retinoic acid synthesis, we examined the ability of ALDH 1 to catalyze the oxidation of the naturally occurring retinal isomers. ALDH1 catalyzed the oxidation of all-trans, 9-cis, and 13-cis retinal with equal efficiency. However, the affinity to all-trans retinal (Km = 2.2 microM) was twofold higher than to 9-cis (Km = 5.5 microM) and 13-cis (Km = 4.6 microM) retinal. All-trans retinol was a potent inhibitor of ALDH1 activity, and inhibited all-trans retinal oxidation uncompetitively. Comparison of the kinetic properties of ALDH1 for retinal isomers with those of previously reported rat kidney retinal dehydrogenase showed distinct differences, suggesting that ALDH1 may play a different role in retinal metabolism in liver.

Changing patterns of renal retinal dehydrogenase expression parallel nephron development in the rat.

We have recently characterized a cytosolic aldehyde dehydrogenase from rat kidney that functions as a retinal dehydrogenase (RALDH) and have cloned the corresponding gene. RALDH catalyzes the oxidation of retinal to retinoic acid, which regulates cell growth and differentiation by activating retinoic acid receptors. In situ hybridization demonstrates that RALDH mRNA expression is prominent in kidney in 2-day-old rats, is detected in lung and in epithelia of several tissues, but is not found in liver tissue. Retinal dehydrogenase activity peaks in kidney at Day 2 after birth and decreases gradually until adulthood, correlating well with RALDH expression. Weaker activity is also detectable in lungs but not in liver. Notably, distribution patterns of RALDH in kidney tissues are dramatically altered during postnatal development (P). From P0 to P6, hybridization is essentially concentrated within the marginal nephrogenic zone of the cortex. Expression progresses to deeper cortical layers from P12 to P16 and is intense in the medulla at P42, and focal expression is still detectable in the cortex. Immunocytochemical localization of RALDH in neonatal kidney shows staining mostly in cortical zone convoluted tubules and in adult rat shows staining in segments of distal and proximal tubules. These data suggest an important role for RALDH in modulating retinoic acid levels in different cell types during rat kidney development. The changing patterns of RALDH expression mirror stages of nephron formation in the developing rat kidney, strongly suggesting a central role for RALDH and thus for retinoids in controlling kidney development.

Differentiation-dependent regulation of retinal dehydrogenase gene expression in the trachea.

Retinoic acid (RA), a metabolite of vitamin A, is known to be a key signaling molecule in regulating epithelial cell differentiation. We recently characterized and cloned a retinal dehydrogenase (RALDH) that catalyzes the oxidation of retinal to RA. In this study, we investigated the effects of retinoids on the level of RALDH mRNA and protein as well as RALDH activity in the trachea and cultured tracheal epithelial cells. Vitamin A deficiency induced squamous metaplasia in the tracheal epithelium and down-regulated RALDH expression. Supplementation of retinol and retinoic acid to vitamin A deficient rats restored the normal mucociliary epithelium and up-regulated the RALDH expression. In rat epithelial cells cultured in vitro, RAinhibited squamous differentiation and promoted mucociliary differentiation. Squamous differentiated cultures (RA-) expressed very low levels of RALDH mRNA, whereas mucociliary differentiated cultures (RA+) expressed high levels of RALDH mRNA. Retinal and retinol were poor inducers of mucociliary differentiation as well as RALDH expression. The RALDH expression paralleled the expression of the mucin-1 gene in mucociliary cultures. These results suggest that the expression of RALDH is dependent on the differentiation state of the airway epithelium.

Retinal dehydrogenase gene expression in stomach and small intestine of rats during postnatal development and in vitamin A deficiency.

Retinal dehydrogenase (RALDH) catalyzes the oxidation of retinal to all-trans and 9-cis retinoic acid, which function as ligands controlling RAR and RXR nuclear receptor-signaling pathways. We have recently shown the expression of RALDH transcript in the stomach and small intestine by reverse transcription polymerase chain reaction [Bhat, P.V., Labrecque J., Dumas, F., Lacroix, A. and Yoshida, A. (1995) Gene 166, 303-306]. We have examined RALDH expression in the stomach and small intestine before and during postnatal development and in vitamin A deficiency by assaying for mRNA levels and protein as well as for enzyme activity. In -2 day fetuses, RALDH expression was high in the small intestine, whereas RALDH protein was not detectable in the stomach. However, expression of RALDH was seen in the stomach after birth, and gradually increased with age and reached the highest level at postnatal day 42. In the intestine, RALDH expression decreased postnatally. Vitamin A deficiency up-regulated RALDH expression in the stomach and small intestine, and administration of retinoids down-regulated the RALDH expression in these tissues. These results show the differential expression of RALDH in the stomach and small intestine during postnatal development, and that vitamin A status regulates the expression of RALDH gene in these tissues.

Tissue concentrations of retinol, retinyl esters, and retinoic acid in vitamin A deficient rats administered a single dose of radioactive retinol.

The tissue concentration of retinol and its metabolites was determined in a group of vitamin A deficient rats after a single dose of 53 micrograms of [11,12-3H]retinol. The sensitive technique of high performance liquid chromatography was used to analyse the metabolites of retinol. The analysis of the metabolites in tissues at different days after the administration of radioactive retinol showed a rapid decrease in the amount of retinol and retinyl esters in the liver tissue, accompanied by an increase in the retinol and retinyl ester values in the kidney. In addition, the content of retinoic acid was higher in liver and kidney compared with intestine, testis, and blood. It reached maximum at 4 and 11 days, respectively. After 17 days the retinoid(s) concentrations decreased markedly in all tissues studied; yet the kidney showed higher concentrations of retinoic acid and retinyl esters. These studies indicate that the kidney retains more vitamin A as vitamin A becomes depleted in the body, probably as a reserve for the production of the active metabolite retinoic acid, needed for the growth and differentiation.

Purification and partial characterization of bovine kidney aldehyde dehydrogenase able to oxidize retinal to retinoic acid.

A NAD-dependent enzyme that catalyzes the oxidation of retinal to retinoic acid has been purified to homogeneity from bovine kidney. The procedures used in the purification included ion-exchange chromatography on DEAE-Sepharose, affinity chromatography on Affi-gel blue and chromatography on a Mono-Q anion-exchange column. On the Mono-Q column, the enzyme aldehyde dehydrogenase (ALDH) resolved into two activity peaks designated as ALDH1 and ALDH2. The enzymes ALDH1 and ALDH2 were purified about 114- and 65-fold, respectively. Gel filtration chromatography of the partially purified native enzyme on Sephacryl S-200 HR exhibited a molecular mass of about 108 kDa. Electrophoresis of the purified enzymes under nondenaturing conditions showed a single protein band. However, sodium dodecyl sulfate--polyacrylamide gel electrophorsis indicated three protein bands in the 55, 30, and 22 kDa molecular mass regions. Both enzymes exhibited a broad substrate specificity oxidizing a wide variety of aliphatic and aromatic aldehydes. The ALDH1 enzyme had a pI of 7.45 and exhibited a low Km (6.37 microM) for retinal, while the ALDH2 enzyme was found to have very low Km for acetaldehyde (0.98 microM). Based on its kinetic properties, it is suggested that the ALDH1 enzyme may be the primary enzyme for oxidizing retinal to retinoic acid in bovine kidney.

Cloning of a cDNA encoding rat aldehyde dehydrogenase with high activity for retinal oxidation.

Retinoic acid (RA), an important regulator of cell differentiation, is biosynthesized from retinol via retinal by a two-step oxidation process. We previously reported the purification and partial amino acid (aa) sequence of a rat kidney aldehyde dehydrogenase (ALDH) isozyme that catalyzed the oxidation of 9-cis and all-trans retinal to corresponding RA with high efficiency [Labrecque et al. Biochem. J. 305 (1995) 681-684]. A rat kidney cDNA library was screened using a 291-bp PCR product generated from total kidney RNA using a pair of oligodeoxyribonucleotide primers matched with the aa sequence. The full-length rat kidney ALDH cDNA contains a 2315-bp (501 aa) open reading frame (ORF). The aa sequence of rat kidney ALDH is 89, 96 and 87% identical to that of the rat cytosolic ALDH, the mouse cytosolic ALDH and human cytosolic ALDH, respectively. Northern blot and RT-PCR-mediated analysis demonstrated that rat kidney ALDH is strongly expressed in kidney, lung, testis, intestine, stomach and trachea, but weakly in the liver.

A novel isoenzyme of aldehyde dehydrogenase specifically involved in the biosynthesis of 9-cis and all-trans retinoic acid.

The pleiotropic effects of retinoids are mediated by two families of nuclear receptors: RAR (retinoic acid receptors) and RXR (retinoid X receptors). 9-cis-Retinoic acid is a specific ligand for RXR receptors, whereas either 9-cis- or all-trans-retinoic acid activates the RAR receptor family. The existence of RXRs suggests a new role for isomerization in the biology of retinoic acid. We report here the identification of an aldehyde dehydrogenase in the rat kidney that catalysed the oxidation of 9-cis- and all-trans-retinal to corresponding retinoic acids with high efficiency, 9-cis-retinal being 2-fold more active than all-trans-retinal. Based on several criteria, such as amino acid sequence, pH optimum, and inhibition by chloral hydrate, this enzyme was found to be a novel isoenzyme of aldehyde dehydrogenase. 9-cis-Retinol, the precursor for the biosynthesis of 9-cis-retinal was identified in the rat kidney. The occurrence of endogenous 9-cis-retinol and the existence of specific dehydrogenase which participates in the catalysis of 9-cis-retinal suggest that all-trans-retinoi(d) isomerization to 9-cis-retinoi(d) occurs at the retinol level, analogous to all-trans-retinol isomerization to 11-cis-retinol in the visual cycle.

Dietary restriction reduces the incidence of NMU-induced mammary tumors and alters retinoid tissue concentrations in rats.

Previous studies suggested a relationship between dietary restriction (DR) effects on mammary carcinogenesis and DR effects on liver retinoids. Therefore, in this study, retinoid concentrations were measured by high-performance liquid chromatography in the plasma, liver, and peripheral organs of DR rats with chemically induced carcinogenesis. Rats were injected with N-methyl-N-nitrosourea (MNU) and maintained on graded levels of DR (reduction of 10-40% from energy ingested by control animals with free access to food). Mammary tumor incidence and multiplicity induced by MNU were reduced in relation to the degree of DR, with virtual prevention occurring at 30% and 40% DR. Total hepatic retinoid concentrations (retinol + retinyl esters) were significantly greater in rats given MNU and subjected to DR, but liver total retinoid content was comparable between the groups. However, plasma retinol concentrations were significantly lower in DR rats than in controls given the carcinogen without DR. Retinoid concentrations were also elevated in adipose tissue, lungs, and intestine of DR rats, while renal concentrations remained unaltered. Retinoid concentrations in mammary glands and mammary tumors were similar in all groups. Thus, in DR rats, vitamin A concentrations in liver and other target tissues are maintained or increased despite decreases in plasma. It remains to be investigated whether these alterations in retinoid content have any relationship to the cancer-preventive effect of DR.

Purification and partial characterization of a rat kidney aldehyde dehydrogenase that oxidizes retinal to retinoic acid.

A NAD-dependent aldehyde dehydrogenase (EC 1.2.1.3) which catalyzes the oxidation of retinal to retinoic acid was purified to homogeneity from rat kidney by using Affi-Gel blue affinity chromatography and chromatofocusing, followed by Mono-Q anion-exchange chromatography. The apparent molecular weight of the native enzyme determined by size-exclusion fast protein liquid chromatography was 140,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave a subunit molecular weight of 53,000. The isoelectric point as measured by chromatofocusing was 8.5. The enzyme also catalyzed the oxidation of acetaldehyde, but showed much lower Km value for the retinal substrate. We suggest that aldehyde dehydrogenase found in the kidney may be a specific retinal dehydrogenase, involved in vitamin A metabolism.

Effect of dietary restriction on hepatic vitamin A content in aging rats.

The size and number of fat-storing cells (FSC), considered to be the main liver storage site of vitamin A, as well as hepatic vitamin A content, were studied in aging female Sprague-Dawley rats subjected soon after weaning to dietary restriction (R), that is, 60% of food consumed by their ad libitum-fed controls (A). In A or R rats, the FSC index (number of cells per 1000 hepatocytes) and volume density (% of hepatic volume) were increased significantly at 24-27 months compared with the younger age groups. The lipocyte index and volume density were also found to be significantly higher, after the first year, in R rats when compared to corresponding age-matched A controls. An increase in total vitamin A content was also noted with age in both groups. R rats exhibited higher retinol, retinyl ester, and total retinoid content than their corresponding controls, but the differences were statistically significant only at 12-14 and 24-27 months. These results indicate that, during aging, dietary restriction markedly increases vitamin A content in liver tissue, a change that may be relevant to the beneficial effect of this dietary manipulation on liver function.

Effects of retinoic acid on the concentrations of radioactive metabolites of retinol in tissues of rats maintained on a retinol-deficient diet.

The effects of feeding retinoic acid for 2 and 6 days on the metabolism of labeled retinol in tissues of rats maintained on a vitamin A deficient diet was studied. The metabolites of retinol were analyzed by high performance liquid chromatography. Feeding retinoic acid for 2 days significantly reduced the blood retinol and retinyl ester levels without affecting the vitamin A content of the liver. In intestine and testis the content of labeled retinoic acid was decreased significantly by dietary retinoic acid. Addition of retinoic acid to the diet for 6 days resulted, in addition to decreased blood retinol and retinyl ester values, in an increase in the retinyl ester values in the liver. The accumulation of retinyl ester in the retinoic acid fed rat liver was accompanied by an absence of labeled retinoic acid. Kidney tissue was found to contain the highest levels of labeled retinoic acid, retinol, and retinyl esters; dietary retinoic acid did not alter the concentrations of these retinoids in the kidney during the experimental period. Since kidney retained more vitamin A when the liver vitamin A was low and also dietary retinoic acid did not affect the concentrations of radioactive retinoic acid in the kidney, it is suggested that the kidney may play a major role in the production of retinoic acid from retinol in the body.

Inhibition of growth of established N-methyl-N-nitrosourea-induced mammary cancer in rats by retinoic acid and ovariectomy.

Retinoids are effective in the prevention of N-methyl-N-nitrosourea-induced mammary carcinoma; retinoids and hormonal therapy exert synergy in cancer prevention. In this study, we examined the effects of the dietary supplementation with all-trans retinoic acid (RA) alone or in combination with ovariectomy on the growth of established N-methyl-N- nitrosourea-induced mammary carcinomas in rats. In the first experiment, animals (n = 13) were entered in each of the following treatment groups when their tumors reached 2 cm in diameter: 1, control diet; 2, RA 300 mg/kg diet; 3, ovariectomy (OVX); 4, RA 300 mg/kg diet plus OVX. Animals were sacrificed after 28 days of therapy. In the RA-supplemented animals, tumor progression was less than in the control group without signs of toxicity as assessed by total and individual tumor surface area and weight, and animal weight. OVX produced tumor regression that was not enhanced by the addition of RA. In a second experiment, RA 65- and 130-mg/kg diets were dissolved in corn oil with antioxidants prior to mixing to the diet to improve biodisponibility. This resulted in overall stabilization of tumor growth by RA addition to the diet at either of the 2 doses utilized; the addition of RA 65 mg/kg diet did not modify tumor regression induced by OVX. In conclusion, the dietary supplementation with RA decreased the progression or stabilized the growth of the majority of tumors and only rarely (6%) induced tumor regression; no additive or synergistic effects were found with the combination of RA and ovariectomy.

Metabolism of retinol and retinoic acid in N-methyl-N-nitrosourea-induced mammary carcinomas in rats.

This study was conducted to examine the in vivo uptake and metabolism of natural retinoids by N-methyl-N-nitrosourea-induced mammary carcinomas. In this study, endogenous retinol and retinyl esters were present in normal mammary epithelial cells, but were undetectable in N-methyl-N-nitrosourea-induced mammary carcinomas in rats as determined by high-pressure liquid chromatography. No differences were found in plasma levels of retinol, in liver retinyl esters, or total content of vitamin A between tumor-bearing and control animals. Administered labeled retinol was taken up and esterified by normal mammary epithelial cells. Tumor-bearing rats were given injections i.p. of either [3H]retinol or [3H]retinoic acid. Radioactivity increased progressively with time in liver and other tissues except in breast tumor, where the uptake fluctuated over the 8 days after the injection of [3H]retinol; in mammary tumors practically no metabolism of [3H]retinol occurred, while in other tissues extensive esterification was detectable. In contrast, in animals given injections of [3H]retinoic acid, the uptake and metabolism of the label in the breast tumors paralleled with those found in other tissues. Neither the activity of acyl coenzyme A:retinol acyl transferase nor the activity of retinyl ester hydrolase was altered in the mammary tumor compared to the normal mammary gland. On the other hand, a significant decrease in the retinal oxidase activity was found in tumor tissue compared to normal mammary tissue. Since no esterification of [3H]retinol occurred in vivo despite the presence of acyl coenzyme A:retinol acyl transferase activity, it is possible that a specific defect in the cellular uptake of retinol may exist in N-methyl-N-nitrosourea-induced mammary carcinomas.

Properties of retinal-oxidizing enzyme activity in rat kidney.

An enzyme activity which converts retinal to retinoic acid was found in the cytosol of rat kidney. The oxidation of retinal was pH-, temperature-, time- and protein-dependent. Under the assay conditions employed, the oxidase activity had an apparent Km of 125 microM toward all-trans retinal. n-Propylgallate, butylated hydroxytoluene and quinacrine inhibited the reaction. The inhibition caused by quinacrine can be partly reversed by FAD. p-Hydroxymercuribenzoate, a sulfhydryl cross-linking agent, was a potent inhibitor. 4'-(9-Acridinylamino)methanesulfon-anisidide, an inhibitor of aldehyde oxidase, inhibited the reaction by 77% at a concentration of 3 mM. All-trans retinal reversed the inhibition caused by acetaldehyde and 2-aminobenzaldehyde. Retinol inhibited the reaction, but retinoic acid did not. The specific activity of the enzyme was increased by vitamin A deficiency. These data indicate that retinal-oxidizing enzyme activity found in the kidney is a sulfhydryl flavoprotein and its activity is dependent on the vitamin A levels of the tissues.