Assessing ureolytic bacteria with calcifying abilities isolated from limestone caves for biocalcification.

Biocalcification through the use of ureolytic bacteria and biochemical activities has evolved in recent decades into a fervent resourceful effective technology suitable for soil stabilization, crack repair and bioremediation. Extensive studies have been carried out on numerous ureolytic bacterial species isolated from soils and sewage samples. However, very limited attention has been given to limestone caves with natural calcite formations as a possible source for isolation of ureolytic bacteria. In this study, bacterial isolates were recovered from limestone cave samples to determine their suitability for biocalcification. Twenty-seven morphologically distinct bacterial isolates were identified by partial 16S rRNA gene sequencing and their various genetic diversity was characterized according to their phylogenetic affiliations. Based on the molecular identification, Sporosarcina was the most abundant genus among all the ureolytic isolates, while the rest belonged to Pseudogracilibacillus and Bacillus genera. Analytical analysis on urease measurement showed that urease activities for the isolates ranged from 1·130 to 21·513 mol urea hydrolysed per minute, with isolate NB33 achieving the highest value and TSB4 achieving the lowest value. The estimated CaCO3 precipitates for the isolates ranged from 4·04 to 17·26 mg ml-1 , with isolate NB30 achieving the highest value and TSB20 achieving the lowest value. The findings in this study demonstrated that the ureolytic bacteria from limestone caves are promising bio-calcifying agents. SIGNIFICANCE AND IMPACT OF THE STUDY: Ureolytic bacteria continues to play an important role as microbial tools used in geotechnical engineering for soil biocalcification. Microbial strains with the ability to produce urease enzyme and induce calcium carbonate mineral are often isolated from soil, water and sludge samples. However, screening for these essential microbes from extreme regions such as caves are rarely investigated. In this study, native bacteria which were isolated from limestone cave samples are identified and characterized. The findings suggested that these ureolytic bacterial isolates have the potential to serve as suitable alternative microbial agents for soil strengthening and stabilization.

Inflammatory bowel disease cancer surveillance in a tertiary referral hospital: attitudes and practice.

BACKGROUND: Physician adherence to guidelines for colorectal cancer (CRC) surveillance in inflammatory bowel disease (IBD) is often poor. This may lead to adverse patient outcomes and excess endoscopic workload. AIMS: To assess the attitudes and practice of IBD specialists in a tertiary centre towards colonoscopic surveillance. METHODS: First, a questionnaire evaluating attitudes and approach to CRC surveillance was issued to 36 clinicians at one tertiary referral hospital. Second, a retrospective audit of IBD surveillance colonoscopy practice over a 2-year period was performed. RESULTS: Questionnaire response rate was 97%. Sixty-nine per cent of respondents were aware of, and used, Australian guidelines. Surveillance was undertaken by all clinicians in patients with extensive colitis, 83% in patients with left-sided colitis and 51% in patients with proctitis. Seventy-six per cent used chromoendoscopy, and 47% took 10 to 20 random biopsies. Colectomy was considered appropriate in 0% for unifocal low-grade dysplasia, 35% for multifocal low-grade dysplasia and 83% for high-grade dysplasia. Sixty-six per cent would remove elevated dysplastic lesions endoscopically. The audit identified 103 surveillance colonoscopies in 81 patients. Chromoendoscopy was used in 21% of cases, and the median number of random biopsies was 13. Sixty-two per cent of colonoscopies were performed outside the guidelines in relation to colonoscopic frequency. Following colonoscopy, an appropriate recommendation for subsequent surveillance was documented in 40% of cases. CONCLUSIONS: Knowledge and practice of CRC surveillance in IBD vary among specialist clinicians and often deviate from guidelines. Many clinicians perform surveillance earlier and more frequently than recommended. These findings have implications for patient outcomes and workload.

Interaction of the retinol/cellular retinol-binding protein complex with isolated nuclei and nuclear components.

Retinol (vitamin A alcohol) is involved in the proper differentiation of epithelia. The mechanism of this involvement is unknown. We have previously reported that purified cellular retinol-binding (CRBP) will mediate specific binding of retinol to nuclei isolated from rat liver. We now report that pure CRBP delivers retinol to the specific nuclear binding sites without itself remaining bound. Triton X-100-treated nuclei retain the majority of these binding sites. CRBP is also capable of delivering retinol specifically to isolated chromatin with no apparent loss of binding sites, as compared to whole nuclei. CRBP again does not remain bound after transferring retinol to the chromatin binding sites. When isolated nuclei are incubated with [3H]retinol-CRBP, sectioned, and autoradiographed, specifically bound retinol is found distributed throughout the nuclei. Thus, CRBP delivers retinol to the interior of the nucleus, to specific binding sites which are primarily, if not solely, on the chromatin. The binding of retinol to these sites may affect gene expression.

Comparison of the level of cellular retinoid-binding proteins and susceptibility to retinoid-induced growth inhibition of various neoplastic cell lines.

The presence and level of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP) were determined in several neoplastic cell lines. These cells exhibited different degrees of susceptibility to growth inhibition in culture by two retinoids, retinyl acetate and retinoic acid. CRABP was detected in 10 and CRBP in 3 of the 11 tested cell lines. The levels of CRBP and CRABP were in the ranges 15-3,400 and 4-1,290 pmol per 10(9) cells, respectively, as determined by sucrose gradient centrifugation. Cell lines that contained CRABP included S91 and B16 melanomas; Mm5mT and DMBA No. 8 mammary adenocarcinomas; BW5147, BW5147.RicR, and P3 neoplastic lymphoid cells; F361.2 (a hybrid cell line obtained by fusion of MSV3T3 and BW5147); MSV3T3 sarcoma; and RAW8 lymphosarcoma. All but the last two cell lines were inhibited by retinoic acid in culture. CRBP was detected in extracts of S91, Mm5mT, and RAW8. Retinyl acetate inhibited the growth of all cell lines with the exception of RAW8, MSV3T3, and F361.2. No correlation was found between the level of either binding protein and the extent of growth inhibition by either retinyl acetate or retinoic acid. Neither of the binding proteins was detected in L1210-A5 leukemia cells, whose proliferation can be inhibited by both retinyl acetate and retinoic acid. These data indicated that screening cell lines for the presence and level of CRBP and CRABP is not sufficient to predict the susceptibility of cultured cells to growth inhibition by retinoids.

Purification and partial characterization of cellular retinol-binding protein from human liver.

Cellular retinol-binding protein (CRBP) has been purified to homogeneity from normal human liver. The procedures in the purification involved primarily gel filtration and ion exchange chromatography, resulting in a 3000-fold purification with greater than 40% yield. The protein is a single:polypeptide chain with molecular weight of 14,800. The protein binds retinol in a manner which considerably alters its spectrum from that observed in organic solution. Many of the properties of human CRBP including molecular weight, amino acid composition, and spectrum of bound retinol are similar to those observed previously for rat CRBP. The availability of pure human CRBP should aid in elucidating its role in the action of retinol and also is more easily monitoring the considerable changes in level of this protein reported in some human cancers.

Cellular binding proteins for vitamin A in colorectal adenocarcinoma of rat.

Rat colorectal mucosa was examined during the course of carcinogenesis, induced by chronic administration of 1,2-dimethylhydrazine (DMH), for the presence and amount of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein. These two binding proteins are implicated in the action of vitamin A in normal and neoplastic tissue. Induced adenocarcinomas were found to contain low levels of cellular retinoic acid-binding protein (10 pmol/g), similar to the levels found in adjacent mucosa of the same animal and also in colorectal mucosa from normal rats or rats chronically treated with DMH. However, the adenocarcinomas had high levels of CRBP (300 to 500 pmol/g), and these levels were dramatically higher than levels of CRBP in adjacent mucosa of the same animal (40 to 100 pmol/g), colorectal mucosa from normal rats (20 pmol/g), or colorectal mucosa from rats chronically treated with DMH (22 to 25 pmol/g). Consequently, the increase in CRBP occurred only with tumor appearance and not with the general hyperplasia of the crypts caused by DMH administration. The CRBP of the tumor was associated with endogenous retinol (77 to 100% saturation) and was similar to, if not identical with, CRBP of normal tissue, as judged by fluorescence spectra, sedimentation behavior, and elution position on Sephadex G-75.

Retinoic acid biosynthesis by normal human breast epithelium is via aldehyde dehydrogenase 6, absent in MCF-7 cells.

Retinoic acid (RA) is the form of vitamin A that controls differentiation and proliferation of epithelia. Our previous work established that normal breast epithelia synthesize RA from retinol, an ability retained by three immortalized but nontumorigenic cell lines but lost in five of six breast cell lines. In this work, we characterize the cause of this defect in one of the lines, the MCF-7 line. We have determined that the immortalized but nontumorigenic cell line, MTSV1.7, capable of synthesizing RA from both retinol and retinal, contains a retinaldehyde dehydrogenase activity for the second step in RA biosynthesis. We have identified it, after isolation, as a previously described enzyme, aldehyde dehydrogenase 6 (ALDH6). Immunohistochemical analysis of normal human breast with antibodies to ALDH6 showed expression of this enzyme in the glandular epithelia colocalized with cellular RA-binding protein type II, a possible marker for certain cells able to synthesize RA. ALDH6 was not present in MCF-7 cells, and these cells were unable to oxidize retinal to RA in culture. When MCF-7 cells were then transfected with ALDH6, they (re)gained the ability to oxidize retinal to RA as well as some ability to synthesize RA when provided with retinol. This suggests that loss of ALDH6 expression is the defect in RA biosynthesis in these cells. Identification of ALDH6 as the retinaldehyde dehydrogenase present in normal human breast epithelia provides the first tool necessary for studying the loss of RA synthetic ability in cancer cells and the relationship of this process to malignant transformation.

Effects of pharmacological retinoids on several vitamin A-metabolizing enzymes.

Fenretinide (HPR), 13-cis-retinoic acid, and all-trans-retinoic acid are vitamin A derivatives used in the treatment of cancer and severe acne. Patients taking these drugs often show side effects resembling the symptoms of hypovitaminosis A, namely, night blindness and decreased plasma retinol levels. A dietary vitamin A deficiency is not suspected in these patients; therefore, interference with normal vitamin A metabolism seems likely. The effect of these drugs on two enzymes involved in vitamin A metabolism was investigated. At micromolar concentrations, all three derivatives were found to inhibit intestinal lecithin-retinol acyltransferase (LRAT) and to a lesser extent liver LRAT and intestinal retinal reductase. Inhibition of intestinal LRAT by HPR and 13-cis-retinoic acid was enhanced by preincubation prior to assay, whereas inhibition of the other activities was not. The Ki for the inhibition of intestinal LRAT by HPR was determined to be 24.1 +/- 5.6 microM. The ability of these drugs to inhibit retinal reduction and retinol esterification in vitro suggests an ability to interfere with normal vitamin A metabolism in vivo, particularly during absorption. This may be most significant for HPR, which is known to accumulate in the liver and intestine after chronic dosing.

Plasma retinol binding protein: structure and function of the prototypic lipocalin.

In terms of both structure and biological function, retinol binding protein (RBP) is one of the best characterized members of the lipocalin superfamily. The molecular interactions in which RBP participates are described herein.

Identification of a mechanism to localize generation of retinoic acid in rat embryos.

Vitamin A (retinol) is essential for normal mammalian development. However, its biological activity depends upon its conversion to retinoic acid (RA), a local mediator of cellular proliferation and differentiation. Previous studies have shown that embryonic RA is found specifically in tissues known to depend upon vitamin A for normal development and that its production follows uptake of maternal retinol. The aim of this study was to identify the mechanism for tissue-specific generation of RA in developing rat embryos. Here we show immunohistochemical localization of the retinol binding protein receptor, cellular retinol binding protein, retinol dehydrogenase and retinal dehydrogenase in rat embryos (presomitic to the 25-30 somite pair stage). These proteins are proposed to be responsible for cellular uptake of retinol, its intracellular transport and its conversion to RA. Thus, they potentially constitute the entire metabolic pathway from vitamin A to RA. All four proteins were detected specifically in tissues that are known to depend upon vitamin A for normal development including the yolk sac, heart, gut, notochord, somites, sensory placodes and the limb. Furthermore, our previous studies have demonstrated that uptake of retinol into the yolk sac depends upon a retinol binding protein receptor. Here we provide evidence that this mechanism functions also in the heart. Colocalization of cellular retinol binding protein, retinol and retinal dehydrogenase with the retinol binding protein receptor in tissues dependent upon vitamin A for normal development suggests that coordinate functioning of these proteins is responsible for cellular uptake of circulating retinol and its metabolism to RA. This is the first evidence of a tissue-specific mechanism for generation of RA from its precursor retinol in the developing embryo.

Inducible expression of cellular retinoic acid-binding protein II in rat ovary: gonadotropin regulation during luteal development.

Two members of the superfamily of small intracellular carrier proteins for lipophilic compounds are cellular retinoic acid-binding protein and cellular retinoic acid-binding protein II [CRABP(II)]. CRABP is found in many adult tissues, whereas CRABP(II) is more restricted and is reported as abundant primarily in skin. Here we report a much greater expression of CRABP(II) in rat corpus luteum than in any other organ/tissue examined, including skin. A rat complementary DNA clone encoding CRABP(II) was isolated and the ovarian expression followed during gonadotropin induction of follicular development in the pseudopregnant rat. The pattern of rat CRABP(II) messenger RNA and protein expression correlated with the appearance of corpora lutea and the rise in progesterone production as the corpora lutea developed, and was similar to the induction of 3 beta-hydroxysteroid dehydrogenase. Immunohistochemical localization revealed that CRABP(II) appeared in luteal cells and was dramatically restricted to their cytoplasmic compartment, with no apparent presence in the nucleus. This suggests that CRABP(II) may be expressed to restrict retinoic acid from occupying nuclear retinoic acid receptors, implying that the differentiation and maintenance of the rat corpus luteum may involve in part a release of certain pathways from retinoid suppression.

Localization of cellular retinoic acid-binding protein (CRABP) II and CRABP in developing rat testis.

Retinoic acid (RA) has been implicated as a signaling molecule for the morphogenesis of some tissues and organs. The morphogenesis of the rat testis occurs relatively late in development, culminating in puberty. Two members of the superfamily of small intracellular carrier proteins for lipophilic compounds are cellular Ra-binding protein (CRABP) and cellular RA-binding protein II (CRABP-II). Both CRABP and CRABP-II are present at various sites in the developing mouse embryo. Here we report the developmental expression and localization of CRABP and CRABP-II in rat testis. Northern blot analysis of CRABP-II demonstrated the highest messenger RNA expression on day 4 (the earliest time point assayed by this technique), decreasing thereafter until day 20, when it became undetectable. Western blot analysis, begun on day 19 of fetal development, indicated that high levels of protein expression in the testis already existed at that time. CRABP messenger RNA expression reached its highest levels between postnatal days 16-20 and decreased thereafter. Immunolocalization revealed that CRABP-II was confined to the fetal population of Leydig and Sertoli cells. We observed that CRABP-II was expressed in certain cells that synthesized retinoic acid in the uterus and ovary (unpublished). The expression of CRABP-II in Sertoli cells and fetal Leydig cells suggested that these cells may well be the site of RA synthesis in the developing testis. CRABP was localized to gonocytes in earlier stages and spermatogonia later, where it was clearly excluded from the nucleus, indicating that the role of CRABP may be to protect these cells from the effects of RA. The reported expression of CRABP-II in embryonal tissues, which are RA responsive and undergoing morphogenesis, coupled with CRABP-II expression in the testis at a critical morphogenic stage suggest that RA may play a prominent role in the morphogenesis of the testis.

Retinoic acid synthesis and expression of cellular retinol-binding protein and cellular retinoic acid-binding protein type II are concurrent with decidualization of rat uterine stromal cells.

Decidualization of stromal cells at the site of embryo implantation in the rat uterus is accompanied by expression of cellular retinol-binding protein and cellular retinoic acid-binding protein [CRABP(II)], whose presence has been shown to correlate with gain of ability to synthesize retinoic acid in other cells. Here we examined whether decidual cells also acquired the ability to synthesize retinoic acid, which would have important implications for understanding the implantation process. Decidual cells were isolated from the uterus on day 8 of pregnancy and cultured. When provided with retinol, they indeed synthesized and released retinoic acid to the medium. To follow acquisition of this ability more closely, artificial induction of decidualization was exploited. Ovariectomized rats were placed on a hormonal regimen that allows decidualization to occur in vivo, with oil stimulation, or in vitro, if cells are isolated on day 5 of the regimen and then cultured. Decidualization in vivo reproduced the expression of cellular retinol-binding protein and CRABP(II) seen during pregnancy. Stromal cells isolated on regimen day 2 synthesized little retinoic acid and expressed little alkaline phosphatase, a marker of decidualization. Stromal cells isolated on regimen day 5 had elevated levels of alkaline phosphatase, increasing during the 3 days of culture examined. The ability of the stromal cells to synthesize retinoic acid showed the same pattern: a substantially elevated production from that previously observed, on day 2, with production increasing significantly over the next 2 culture days. Thus, expression of CRABP(II) was correlated with gain of ability to synthesize retinoic acid. Retinoid signaling may be an important part of the process of embryo implantation.

Molecular cloning and hormonal regulation of a murine epididymal retinoic acid-binding protein messenger ribonucleic acid.

A complementary DNA encoding the mouse epididymal secretory protein MEP 10 (mouse epididymal protein 10) was cloned and is now renamed murine epididymal retinoic acid binding protein (mE-RABP). The analysis of the predicted primary amino acid sequence showed that mE-RABP has a 75% identity with rat ESP I (epididymal secretory protein I), another epididymal retinoic acid-binding protein. The homology strongly suggests that mE-RABP is the mouse orthologue of rat ESP I. A computer analysis of the predicted three-dimensional structure confirmed that mE-RABP can accommodate retinoic acid as ligand. In the rat, ESP I messenger RNA (mRNA) is expressed in the efferent ducts and in the entire caput epididymidis. However, in the mouse, the expression of a 950-bp mE-RABP mRNA was detected only in principal cells of the mid/distal caput epididymidis, suggesting that the regulation of region-specific expression is different in rat and mouse. Northern blot analyses showed that mE-RABP gene expression is no longer detected 10 days after castration but progressively rebounds between days 15 and 60. However, mE-RABP protein could not be detected by Western blot 30 days after castration. Androgen replacement, begun 5 days after castration and continued for 4 days restored significant expression of mE-RABP mRNA. Efferent duct ligation for 10 days did not affect gene expression. Taken together, these results indicate that mE-RABP mRNA expression is regulated by androgens but not by testicular factors. The overall similarity in the primary amino acid sequence of mE-RABP with ESP I and other members of the lipocalin superfamily suggests that they are evolutionarily related.

Gene duplication gives rise to a new 17-kilodalton lipocalin that shows epididymal region-specific expression and testicular factor(s) regulation.

Using transgenic mice, we have recently shown that 5 kb of the 5'-flanking region of the mouse epididymal retinoic acid-binding protein (mE-RABP) gene contains all of the information required for spatial and temporal gene expression in the epididymis. To identify the important cis-DNA regulatory element(s) involved in the tissue-, region-, and cell-specific expression of the mE-RABP gene, the 5-kb DNA fragment was sequenced. A computer analysis of the nucleotide sequence showed the presence of a new gene located 1.7 kb upstream from the mE-RABP gene transcription initiation site. The analysis of the open reading frame showed that the new gene encoded a putative 17-kDa lipocalin (named mEP17) related to mE-RABP. A 600-bp complementary DNA encoding mEP17 was cloned by rapid amplification of 3'-cDNA ends from epididymal total RNA. Two mEP17 RNA species (1 and 3.1 kb in size) were detected by Northern blot in the epididymis, but not in other tissues tested. In situ hybridization analyses showed that, unlike mE-RABP messenger RNA (mRNA), which is expressed in the distal caput epididymidis, mEP17 mRNA was detected only in the principal cells of the initial segment. The spatial expression and homology with mE-RABP suggest that mEP17 may act as a retinoid carrier protein within the epididymis. mEP17 mRNA expression disappeared 5 days postcastration. Four days after unilateral castration, mEP17 mRNA had nearly disappeared in the epididymis from the castrated side, but not from the intact side. In addition, testosterone replacement to bilaterally castrated mice failed to restore gene expression. We conclude that mEP17 gene expression is dependent on testicular factors circulating in the luminal fluid. Together our results suggest that mE-RABP and mEP17 genes were generated by duplication and that evolution led to a different region-specific gene expression and regulation in the epididymis.

Regulation and localization of cellular retinol-binding protein, retinol-binding protein, cellular retinoic acid-binding protein (CRABP), and CRABP II in the uterus of the pseudopregnant rat.

Three members of the superfamily of small intracellular carrier proteins for lipophilic compounds are cellular retinol-binding protein (CRBP), cellular retinoic acid-binding protein (CRABP), and cellular retinoic acid-binding protein II (CRABP II). Retinol-binding protein (RBP) is a secreted protein that binds and solubilizes vitamin A for transport. Here we report the coordinate regulation of RBP, CRBP, retinol, and CRABP II in the uterus of the pseudopregnant rat. In the proliferative stage of the uterus, which was induced by PMSG, the messenger RNA (mRNA) and protein levels of RBP and CRBP as well as retinol levels significantly decreased. This pattern of regulation was duplicated by estrogen treatment of prepubertal rats. In addition, CRBP and RBP were found to be colocalized to the stromal cells of the rat uterus by immunohistochemistry and [35S]methionine-labeled affinity chromatography, respectively, and were not detected in other cell populations. CRABP II mRNA and protein expression were up-regulated in the proliferative phase of the uterus brought about by PMSG injection or, alternatively, by estrogen treatment of prepubertal rats. CRABP II was localized to the surface epithelium, but was not seen elsewhere, including glandular epithelium. Immunolocalization of CRABP showed staining of the smooth muscle and stromal cells of the uterus. The appearance of CRABP in the stroma of the uterus also correlated with PMSG injection as well as estrogen treatment. Although estrogen induced the appearance of both binding proteins, CRABP mRNA levels peaked between 4-24 h postestrogen treatment, whereas CRABP II mRNA levels continued to rise 48 h postestrogen treatment. These data demonstrate an important role for vitamin A and retinoid-binding proteins in rat uterine physiology.

Cellular retinoic acid binding protein is associated with mitochondria.

We report that immunohistochemical staining for cellular retinoic acid-binding protein (CRABP) was restricted to the cytoplasm of cortical cells in bovine adrenal. In contrast, staining for the similar protein, cellular retinol-binding protein (CRBP), was found throughout these cells. After transfections of CRABP and CRBP into cultured cells, immunofluorescence analyses again revealed cytoplasmic restriction only for CRABP, with a pronounced punctate appearance. Use of organelle-specific fluorochromes indicated that CRABP immunofluorescence overlaid exactly with the pattern of the mitochondrial-specific fluorochrome. Confirmation of this association came with subcellular fractionation of the adrenal cortex. CRABP, but not CRBP, co-sedimented with the mitochondria, a novel finding for a member of this superfamily of cellular lipid-binding proteins.

Quantitation of cellular retinol-binding protein in human organs.

Levels of cellular retinol-binding protein (CRBP) have been determined for a number of human tissues by a sensitive radioimmunoassay. The protein was detectable in at least one sample of every tissue examined. Samples with the highest levels were obtained from adrenal, liver, ovary, pituitary, and testis. The relative abundance of CRBP was significantly different from the relative abundance for rat organs. The wide distribution of CRBP in human organs stresses the importance of this protein in the metabolism of vitamin A throughout the body.

Intestinal uptake of retinol: enhancement by bovine milk beta-lactoglobulin.

The effect of bovine milk beta-lactoglobulin (BLG) on intestinal uptake of retinol was examined in suckling rats with the everted sac technique. Uptake of 0.06 mumol retinol/L bound to BLG (BLG-retinol) was significantly (p less than 0.01) higher than that of 0.06 mumol free retinol/L both in the jejunum and the ileum. The enhancing effect of BLG on retinol uptake was specific because equimolar concentrations of bovine serum albumin and lactoferrin had no effect on retinol uptake. However, serum retinol-binding protein (RBP), which shares structural and conformational similarities with BLG, also enhanced retinol uptake. BLG, BLG-retinol, and RBP-retinol all inhibited the uptake of retinol from BLG-[3H]retinol in a concentration-dependent manner. Uptake of retinol from BLG-retinol was saturable (apparent Km = 5.6 mumol/L, Vmax = 22.7 nmol.g-1.5 min-1), not affected by metabolic inhibitors, and partially temperature dependent (Q10 = 2.77). BLG also significantly (p less than 0.01) enhanced retinol uptake in the intestine of adult rats. These results demonstrate that BLG specifically enhances intestinal uptake of retinol and suggest the possibility of a receptor for BLG-like proteins at the brush border membrane of the enterocyte.

Retinyl ester hydrolytic activity associated with human intestinal brush border membranes.

Hydrolysis of retinyl esters in the lumen of the small intestine is required before absorption. Previously, rat brush border membranes (BBMs) were found to contain a pancreatic-derived esterase preferring retinyl esters with short fatty acyl chains and an intrinsic esterase preferring esters with long fatty acyl chains. Here, similar activities were found for preparations of human BBMs. Long-chain ester hydrolysis was stimulated best by deoxycholate, a dihydroxy bile salt, whereas short-chain ester hydrolysis was stimulated best by taurocholate, a trihydroxy bile salt. A 10-fold difference in KM values for retinyl palmitate (0.53 mumol/L) and caproate (5.5 mumol/L) also indicated distinguishable long-chain and short-chain activities. Differences between retinyl butyrate and retinyl caproate hydrolysis suggested the possible presence of two short-chain esterase activities associated with both rat and human BBMs, in addition to the long-chain activity. Similarities between human BBM retinyl ester hydrolytic activities and those observed for rat BBMs suggest that the rat is a good model for humans in this step of vitamin A metabolism.