Expression pattern and localization of β,β-carotene 15,15′-dioxygenase in different tissues

Abstract

Beta,beta-carotene 15,15'-dioxygenase cleaves beta,beta-carotene into two molecules of retinal, and is the key enzyme in the metabolism of beta,beta-carotene to vitamin A. The enzyme has been known for more than 40 years, yet all attempts to purify the protein to homogeneity have failed. Recently, the successful cloning and sequencing of an enzyme with beta,beta-carotene 15,15'-dioxygenase activity from chicken, as well as from Drosophila, has been reported. Here, we describe in detail our attempt to enrich the chicken beta,beta-carotene 15,15'-dioxygenase to such an extent as to allow determination of partial amino acid sequences, which were then used to design degenerate oligonucleotides. Screening of a chicken duodenal expression library yielded a full-length clone containing a coding sequence of 1578 bp. Functional expression in Escherichia coli and in eukaryotic cell lines confirmed that we had cloned the first vertebrate dioxygenase that cleaves beta,beta-carotene at the central 15,15'-double bond. By performing a sequence homology search, the cDNA sequence of the mouse homologue was found as an expressed sequence tag (EST) in the gene bank. At the amino-acid level, the degree of homology between the chicken and mouse sequences is 81%. Thus beta,beta-carotene 15,15'-dioxygenase can be considered as being an enzyme that is evolutionarily rather well conserved. We established the expression pattern of beta,beta-carotene 15,15'-dioxygenase in chicken and mouse tissues with a combination of Northern blots and in situ hybridization. The mRNA for beta,beta-carotene 15,15'-dioxygenase was localized primarily in duodenal villi, as well as in liver and in tubular structures of lung and kidney. These new findings demonstrate that beta,beta-carotene 15,15'-dioxygenase is also expressed in epithelial structures, where it serves to provide the tissue-specific vitamin A supply.

In Vitro Characterization of a Recombinant Blh Protein from an Uncultured Marine Bacterium as a β-Carotene 15,15′-Dioxygenase

“…The enzyme reaction was performed in 100 mM Tricine-KOH buffer (pH 8.0) containing 50 M ␤-carotene and 0.04 unit/ml enzyme at 40°C for 60 min. After incubation, the reaction was stopped by 3.7% (v/v) formaldehyde, and additional incubation was done at 40°C for 10 min (32 was evaluated with and without phenanthroline treatment. To examine the effect of pH on the enzyme activity, the pH was varied between 6.0 and 9.0 using 100 mM potassium phosphate buffer (pH 6.0 -7.0) and 100 mM Tricine-KOH buffer (pH 7.0 -9.0).…”

Carotenoid metabolism in mammals, including man: formation, occurrence, and function of apocarotenoids

“…Given the lack of defi nitive information on the reaction mechanisms, we use ␤ -carotene-oxygenase 1 (BCO1) for BCMO1 and ␤ -caroteneoxygenase 2 (BCO2) for BCDO2. BCO1 has been cloned from the Drosophila melanogaster ( 51 ), chicken ( 50 ), mouse (60)(61)(62), and human ( 63 ). BCO2 has been identifi ed and cloned from mice, humans, and zebrafi sh ( 54 ).…”

Enzymology of retinoic acid biosynthesis and degradation

“…1 ), is expressed in many other adult tissues and in mammalian embryo starting at seven days postconception (112)(113)(114)(115)(116)(117)(118)(119). In mice, BCMO1 is detected at both mRNA and protein levels in liver, kidney, and testis in addition to the small intestine (112)(113)(114)(115)(116). In humans, BCMO1 is detectable by immunohistochemistry in the stomach, small intestine, colon, liver, kidney, skin, skeletal muscle, adrenal gland, pancreas, testis, ovary, prostate, endometrium, mammary tissue ( 117 ), and eyes ( 118,119 ).…”