[Separation, purification and properties of mitochondrial xylitol-dehydrogenases of the guinea pig liver]

Molecular characterization of mammalian dicarbonyl/L-xylulose reductase and its localization in kidney

In this report, we first cloned a cDNA for a protein that is highly expressed in mouse kidney and then isolated its counterparts in human, rat hamster, and guinea pig by polymerase chain reaction-based cloning. The cDNAs of the five species encoded polypeptides of 244 amino acids, which shared more than 85% identity with each other and showed high identity with a human sperm 34-kDa protein, P34H, as well as a murine lung-specific carbonyl reductase of the short-chain dehydrogenase/reductase superfamily. In particular, the human protein is identical to P34H, except for one amino acid substitution. The purified recombinant proteins of the five species were about 100-kDa homotetramers with NADPH-linked reductase activity for alpha-dicarbonyl compounds, catalyzed the oxidoreduction between xylitol and l-xylulose, and were inhibited competitively by n-butyric acid. Therefore, the proteins are designated as dicarbonyl/l-xylulose reductases (DCXRs). The substrate specificity and kinetic constants of DCXRs for dicarbonyl compounds and sugars are similar to those of mammalian diacetyl reductase and l-xylulose reductase, respectively, and the identity of the DCXRs with these two enzymes was demonstrated by their co-purification from hamster and guinea pig livers and by protein sequencing of the hepatic enzymes. Both DCXR and its mRNA are highly expressed in kidney and liver of human and rodent tissues, and the protein was localized primarily to the inner membranes of the proximal renal tubules in murine kidneys. The results imply that P34H and diacetyl reductase (EC ) are identical to l-xylulose reductase (EC ), which is involved in the uronate cycle of glucose metabolism, and the unique localization of the enzyme in kidney suggests that it has a role other than in general carbohydrate metabolism.

Molecular cloning, expression and tissue distribution of hamster diacetyl reductase. Identity with L-xylulose reductase

Using rapid amplification of cDNA ends PCR, a cDNA species for diacetyl reductase (EC 1.1.1.5) was isolated from hamster liver. The encoded protein consisted of 244 amino acids, and showed high sequence identity to mouse lung carbonyl reductase and hamster sperm P26h protein, which belong to the short-chain dehydrogenase/reductase family. The enzyme efficiently reduced L-xylulose as well as diacetyl, and slowly oxidized xylitol. The K(m) values for L-xylulose and xylitol were similar to those reported for L-xylulose reductase (EC 1.1.1.10) of guinea pig liver. The identity of diacetyl reductase with L-xylulose reductase was demonstrated by co-purification of the two enzyme activities from hamster liver and their proportional distribution in other tissues.

Calculation of standard transformed formation properties of biochemical reactants and standard apparent reduction potentials of half reactions

The standard Gibbs energies of formation and standard enthalpies of formation of species involved in biochemical reactions are used to calculate standard transformed Gibbs energies of formation and standard transformed enthalpies of formation of 62 biochemical reactants (sums of species) at 298.15 K, pH 7, and ionic strengths of 0, 0.10, and 0.25 M. It has been possible to put the oxidized and reduced forms of some reactants in this table because their standard apparent reduction potentials are known at pH 7. This paper emphasizes redox reactions. Two applications have been made of these 62 new values of standard transformed Gibbs energies of formation at pH 7: (1) They have been used to calculate standard transformed Gibbs energies of formation of 16 more biochemical reactants from measurements of apparent equilibrium constants of redox reactions. (2) They have been used to calculate standard apparent reduction potentials at pH 7 for half reactions involving reactants discussed in this article and the previous one. This table of standard apparent reduction potentials can be extended considerably from known apparent equilibrium constants for enzyme-catalyzed redox reactions. This brings the total number of reactants for which the standard transformed Gibbs energy of formation at 298K, pH 7, and ionic strengths of 0, 0.10, and 0.25 M have been calculated to 142.

Calculation of standard transformed Gibbs energies and standard transformed enthalpies of biochemical reactants

The standard Gibbs energies of formation and standard enthalpies of formation of species involved in biochemical reactions are used to calculate standard transformed Gibbs energies of formation and standard transformed enthalpies of formation of 53 reactants (sums of species) at 298.15 K, pH 7, and ionic strengths of 0, 0.1, and 0. 25 M. The standard transformed Gibbs energies of formation are used to calculate apparent equilibrium constants K' for 22 biochemical reactions for which apparent equilibrium constants have been determined close to these conditions. This comparison is generally satisfactory given the differences in experimental conditions. The transformed formation properties for the 53 reactants make it possible to calculate transformed formation properties for other reactants involved in biochemical reactions with some of these reactants. This is illustrated by calculating standard transformed Gibbs energies of formation for 11 more reactants without information on the standard Gibbs energies of formation of the species. The list of 64 reactants for which standard transformed Gibbs energies of formation are presented can be considerably extended. The use of tables of standard transformed Gibbs energies of formation to store information on apparent equilibrium constants is more efficient than simply storing apparent equilibrium constants because a reactant can be looked up in a table and may be involved in hundreds of reactions. The effects of magnesium ions on several reactions involving ATP are calculated. The advantages of using enzyme-catalyzed reactions for determining thermodynamic properties of complicated molecules in aqueous solution are discussed.

Histochemical studies on the morphology of the Golgi apparatus and its relation to catecholamine biosynthesis in the locus coeruleus of Rhesus and crab-eating monkeys

Detailed histochemical studies have been conducted on the distribution of thiamine pyrophosphatase (TPPase), L-gulonolactone oxidase (GLO), and NAD-linked xylitol dehydrogenase (XDH) in every component of the Locus coeruleus (LC) of healthy adult male Rhesus and crab-eating monkeys in order to clearify the morphology of the Golgi apparatus (GA) and its relation to biosynthesis of catechol-amines in this special nucleus of the primate (NA nucleus A 6 as defined in the Rhesus monkey by German and Bowden [1975]). Medium-sized neurons of both species of monkeys, which are considered to play an important role in the LC, were classified into 5 groups on the basis of morphological patterns of the GA. Many neurons of both species of monkeys were positive for the XDH test while some neurons of the crab-eating monkey as well as a few neurons of the Rhesus monkey were positive for the GLO reaction. The LC of both species of monkeys must be composed of metabolically one kind of identical medium-sized parasympathetic neurons whose GA may continously undergo 5 distinct phasic changes depending on the functional state of that cell. However, the GA changes its shape much more significantly even within each group of the 5 in the crab-eating monkey than in the Rhesus monkey. The GA Type IV may correspond to the catabolic phase of the GA during which biosynthesis of both catecholamines and vitamin C should be going on. Production of vitamin C may greatly help biosynthesis of catecholamines in LC. The difference in species is evident between the 2 kinds of monkeys studied in regard to the degree of their ability to synthesize these substances. The degree of the ability to synthesize vitamin C parallels the density distribution of Type IV neurons in LC whose GA often develops much more greatly in the crab-eating monkey than in the Rhesus monkey.