Distribution and characterization of dihydrodiol dehydrogenases in mammalian ocular tissues.
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ABSTRACT:
SUBMITTER: Hara A
PROVIDER: S-EPMC1150020 | biostudies-other | 1991 Apr
REPOSITORIES: biostudies-other
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Project description:The properties of 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase from Sprague-Dawley rat liver cytosol have been re-examined in light of several reports which suggest that multiple forms of the enzyme may exist in this tissue. During enzyme purification, chromatography on DE-52 cellulose and chromatofocusing columns indicated the existence of only one form of the protein. Re-chromatography of the purified enzyme by either of these techniques failed to resolve the protein into additional forms. When the purified enzyme was subjected to SDS/polyacrylamide-gel electrophoresis a single band corresponding to Mr 34,000 was detected. Two-dimensional gels showed one predominant protein with a pI of 5.9. Using the homogeneous enzyme as antigen, high-titre polyclonal antibody was raised in rabbits. Western-blot analysis of cytosolic proteins prepared from male and female Sprague-Dawley rat liver indicated the presence of a single immunoreactive band with an Mr of 34,000 in both sexes. All of the 3 alpha-hydroxysteroid dehydrogenase activity present in rat liver cytosol could be immunotitrated with the antibody and the resulting titration curve was superimposable on the titration curve obtained with the purified enzyme. Western-blot analysis of cytosolic proteins prepared from livers of male Wistar and Fischer rats also revealed the presence of a single immunoreactive protein with an Mr of 34,000. These data indicate that, contrary to previous reports, only one form of the dehydrogenase may exist in liver cytosols prepared from a variety of rat strains. Although 3 alpha-hydroxysteroid dehydrogenase activity is known to be widely distributed in male Sprague-Dawley rat tissues, Western blots indicate that only the liver, lung, testis and small intestine contain immunoreactive protein with an Mr of 34,000. The levels of immunoreactive protein in these tissues follow the distribution of dihydrodiol dehydrogenase.
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Project description:Cynomolgus and Japanese monkey kidneys, dog and pig livers and rabbit lens contain dimeric dihydrodiol dehydrogenase (EC 1.3.1.20) associated with high carbonyl reductase activity. Here we have isolated cDNA species for the dimeric enzymes by reverse transcriptase-PCR from human intestine in addition to the above five animal tissues. The amino acid sequences deduced from the monkey, pig and dog cDNA species perfectly matched the partial sequences of peptides digested from the respective enzymes of these animal tissues, and active recombinant proteins were expressed in a bacterial system from the monkey and human cDNA species. Northern blot analysis revealed the existence of a single 1.3 kb mRNA species for the enzyme in these animal tissues. The human enzyme shared 94%, 85%, 84% and 82% amino acid identity with the enzymes of the two monkey strains (their sequences were identical), the dog, the pig and the rabbit respectively. The sequences of the primate enzymes consisted of 335 amino acid residues and lacked one amino acid compared with the other animal enzymes. In contrast with previous reports that other types of dihydrodiol dehydrogenase, carbonyl reductases and enzymes with either activity belong to the aldo-keto reductase family or the short-chain dehydrogenase/reductase family, dimeric dihydrodiol dehydrogenase showed no sequence similarity with the members of the two protein families. The dimeric enzyme aligned with low degrees of identity (14-25%) with several prokaryotic proteins, in which 47 residues are strictly or highly conserved. Thus dimeric dihydrodiol dehydrogenase has a primary structure distinct from the previously known mammalian enzymes and is suggested to constitute a novel protein family with the prokaryotic proteins.
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Project description:BackgroundIn mammals, L-threonine is an indispensable amino acid. The conversion of L-threonine to glycine occurs through a two-step biochemical pathway involving the enzymes L-threonine 3-dehydrogenase and 2-amino-3-ketobutyrate coenzyme A ligase. The L-threonine 3-dehydrogenase enzyme has been purified and characterised, but the L-threonine 3-dehydrogenase gene has not previously been identified in mammals.ResultsTranscripts for L-threonine 3-dehydrogenase from both the mouse and pig are reported. The ORFs of both L-threonine dehydrogenase cDNAs encode proteins of 373 residues (41.5 kDa) and they share 80% identity. The mouse gene is located on chromosome 14, band C. The amino-terminal regions of these proteins have characteristics of a mitochondrial targeting sequence and are related to the UDP-galactose 4-epimerases, with both enzyme families having an amino-terminal NAD+ binding domain. That these cDNAs encode threonine dehydrogenases was shown, previously, by tiling 13 tryptic peptide sequences, obtained from purified L-threonine dehydrogenase isolated from porcine liver mitochondria, on to the pig ORF. These eukaryotic L-threonine dehydrogenases also have significant similarity with the prokaryote L-threonine dehydrogenase amino-terminus peptide sequence of the bacterium, Clostridium sticklandii. In murine tissues, the expression of both L-threonine dehydrogenase and 2-amino-3-ketobutyrate coenzyme A ligase mRNAs were highest in the liver and were also present in brain, heart, kidney, liver, lung, skeletal muscle, spleen and testis.ConclusionsThe first cloning of transcripts for L-threonine dehydrogenase from eukaryotic organisms are reported. However, they do not have any significant sequence homology to the well-characterised Escherichia coli L-threonine dehydrogenase.
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