The cofactor preferences exhibited by the enzymes of the SDR family are mainly determined by the electrostatic environment surrounding the 2'-hydroxyl (or phosphate) group of the adenosine ribose moiety of NADH (or NADPH). Thus, positively charged and negatively charged environments correlate with preference for NADPH and NADH respectively.
We have deduced the entire 575-amino acid sequence of the human thrombomodulin precursor from cDNA clones. The precursor starts with an 18-residue signal peptide domain, followed by the NH2-terminal domain, a domain with six epidermal growth factor-like structures, an 0-glycosylation site-rich domain, a 24-residue transmembrane domain and a cytoplasmic domain. Simian COS cells transfected with the expression vector pSV2 containing thrombomodulin cDNA synthesized immunoreactive and functionally active thrombomodulin.
Human 3alpha-hydroxysteroid dehydrogenase exists in four isoforms, which belong to the aldo-keto reductase (AKR) superfamily and are named AKR1C1-AKR1C4. The properties of AKR1C3 have not been fully characterized compared to the other isoforms. In addition, a cDNA that shows more than 99% homology with AKR1C3 cDNA has been cloned from human myeloblasts. We have here expressed and purified a recombinant enzyme (designated as DBDH) from this cDNA. DBDH oxidized xenobiotic alicyclic alcohols and 3alpha- or 17beta-hydroxy-5beta-androstanes, and catalyzed the reversible conversion between prostaglandin D2 and 9alpha,11beta-prostaglandin F2 more efficiently than that of 3alpha- or 17beta-hydroxysteroids:the respective Km values were 0.6 and 6.8 microM, and kcat/Km values were about 1,000 min-1.mM-1. Anti-inflammatory drugs highly inhibited the enzyme. The recombinant AKR1C3 prepared by site-directed mutagenesis of DBDH also showed the same properties as the wild-type DBDH. Analyses of expression of mRNAs for DBDH and AKR1C3 by reverse transcription-PCR indicated that only one mRNA species for DBDH is expressed in 33 human specimens of liver, kidney, lung, brain, heart, spleen, adrenal gland, small intestine, placenta, prostate, and testis. These results suggest that AKR1C3 acts as prostaglandin D2 11-ketoreductase, and that its principal gene in the human has a coding region represented by DBDH cDNA.
Blood coagulation capacity increases with age in healthy individuals. Through extensive longitudinal analyses of human factor IX gene expression in transgenic mice, two essential age-regulatory elements, AE5' and AE3', have been identified. These elements are required and together are sufficient for normal age regulation of factor IX expression. AE5', a PEA-3 related element present in the 5' upstream region of the gene encoding factor IX, is responsible for age-stable expression of the gene. AE3', in the middle of the 3' untranslated region, is responsible for age-associated elevation in messenger RNA levels. In a concerted manner, AE5' and AE3' recapitulate natural patterns of the advancing age-associated increase in factor IX gene expression.
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