Evidence for the identity of glutathione-dependent formaldehyde dehydrogenase and class III alcohol dehydrogenase

Formaldehyde dehydrogenase (EC 1.2.1.1) is a widely occurring enzyme which catalyzes the oxidation of S-hydroxymethylglutathione, formed from formaldehyde and glutathione, into S-formyglutathione in the presence of NAD. We determined the amino acid sequences for 5 tryptic peptides (containing altogether 57 amino acids) from electrophoretically homogeneous rat liver formaldehyde dehydrogenase and found that they all were exactly homologous to the sequence of rat liver class III alcohol dehydrogenase (ADH-2). Formaldehyde dehydrogenase was found to be able at high pH values to catalyze the NAD-dependent oxidation of long-chain aliphatic alcohols like n-octanol and 12-hydroxydodecanoate but ethanol was used only at very high substrate concentrations and pyrazole was not inhibitory. The amino acid sequence homology and identical structural and kinetic properties indicate that formaldehyde dehydrogenase and the mammalian class III alcohol dehydrogenases are identical enzymes.     

Malate dehydrogenase and lactate dehydrogenase in the serum of hyperthyroxinemic and hypothyroid rats]

In serum of hyperthyroxinemic and hypothyreotic rats the activities of MDH and LDH were investigated. In both groups the level of MDH was significantly elevated in comparison with control animals. The activity of LDH did not show any significant alterations.     

A single cyclohexadienyl dehydrogenase specifies the prephenate dehydrogenase and arogenate dehydrogenase components of the dual pathways to L-tyrosine in Pseudomonas aeruginosa

Dual biosynthetic pathways diverge from prephenate to L-tyrosine in Pseudomonas aeruginosa, with 4-hydroxyphenylpyruvate and L-arogenate being the unique intermediates of these pathways. Prephenate dehydrogenase and arogenate dehydrogenase activities could not be separated throughout fractionation steps yielding a purification of more than 200-fold, and the ratio of activities was constant throughout purification. Thus, the enzyme is a cyclohexadienyl dehydrogenase. The native enzyme has a molecular weight of 150,000 and is a hexamer made up of identical 25,500 subunits. The enzyme is specific for NAD+ as an electron acceptor, and identical Km values of 0.25 mM were obtained for NAD+, regardless of whether activity was assayed as prephenate dehydrogenase or as arogenate dehydrogenase. Km values of 0.07 mM and 0.17 mM were calculated for prephenate and L-arogenate, respectively. Inhibition by L-tyrosine was noncompetitive with respect to NAD+, but was strictly competitive with respect to either prephenate or L-arogenate. With cyclohexadiene as variable substrate, similar Ki values for L-tyrosine of 0.06 mM (prephenate) and 0.05 mM (L-arogenate) were obtained. With NAD+ as the variable substrate, similar Ki values for L-tyrosine of 0.26 mM (prephenate) and 0.28 mM (L-arogenate), respectively, were calculated. This is the first characterization of a purified, monofunctional cyclohexadienyl dehydrogenase.     

Kinetic advantages of hetero-enzyme complexes with glutamate dehydrogenase and the alpha-ketoglutarate dehydrogenase complex

We have found previously (Fahien, L.A., Kmiotek, E.H., MacDonald, M. J., Fibich, B., and Mandic, M. (1988) J. Biol. Chem. 263, 10687-10697) that glutamate-malate oxidation can be enhanced by cooperative binding of mitochondrial aspartate aminotransferase and malate dehydrogenase to the alpha-ketoglutarate dehydrogenase complex. The present results demonstrate that glutamate dehydrogenase, which forms binary complexes with these enzymes, adds to this ternary complex and thereby increases binding of the other enzymes. Kinetic evidence for direct transfer of alpha-ketoglutarate and NADH, within these complexes, has been obtained by measuring steady-state rates of E2 when most of the substrate or coenzyme is bound to the aminotransferase or glutamate dehydrogenase (E1). Rates significantly greater than those which can be accounted for by the concentration of free ligand, calculated from the measured values of the E1-ligand dissociation constants, require that the E1-ligand complex serve as a substrate for E2 (Srivastava, D. K., and Bernhard, S. A. (1986) Curr. Tops. Cell Regul. 28, 1-68). By this criterion, NADH is transferred directly from glutamate dehydrogenase to malate dehydrogenase and alpha-ketoglutarate is channeled from the aminotransferase to both glutamate dehydrogenase and the alpha-ketoglutarate dehydrogenase complex. Similar evidence indicates that GTP bound to an allosteric site on glutamate dehydrogenase functions as a substrate for succinic thiokinase. The potential physiological advantages to channeling of activators and inhibitors as well as substrates within multienzyme complexes organized around the alpha-ketoglutarate dehydrogenase complex are discussed.     

Identity of the subunits and the stoicheiometry of prosthetic groups in trimethylamine dehydrogenase and dimethylamine dehydrogenase.

Trimethylamine dehydrogenases from bacterium W3A1 and Hyphomicrobium X and the dimethylamine dehydrogenase from Hyphomicrobium X were found to contain only one kind of subunit. The millimolar absorption coefficient of a single [4Fe-4S] cluster in trimethylamine dehydrogenase from bacterium W3A1 was estimated to be 14.8 mM-1 . cm-1 at 443 nm. From this value a 1:1 stoicheiometry of the prosthetic groups, 6-S-cysteinyl-FMN and the [4Fe-4S] cluster, was established. Millimolar absorption coefficients of the three enzymes were in the range 49.4-58.7 mM-1 . cm-1 at approx. 440 nm. This range of values is consistent with the presence of two [4Fe-4S] clusters and two flavin residues, for which the millimolar absorption coefficient had earlier been found to be 12.3 mM-1 . cm-1 at 437 nm. The N-terminal amino acid was alanine in each of the three enzymes. Sequence analysis of the first 15 residues from the N-terminus of dimethylamine dehydrogenase indicated a single unique sequence. Two identical subunits, each containing covalently bound 6-S-cysteinyl-FMN and a [4Fe-4S] cluster, in each of the enzymes are therefore indicated.     

Purification and characterization of the molybdoenzymes nicotinate dehydrogenase and 6-hydroxynicotinate dehydrogenase from Bacillus niacini

The enzymes nicotinate dehydrogenase and 6-hydroxynicotinate dehydrogenase from Bacillus niacini could be purified to homogeneity by means of anion exchange chromatography, hydrophobic interaction chromatography, gel filtration, and chromatography on hydroxylapatite. During enrichment procedures both enzymes showed a significant loss in specific activity. The molecular weight of nicotinate dehydrogenase and 6-hydroxynicotinate dehydrogenase was determined to be about 300,000 and 120,000, respectively. They were highly substrate specific and transferred electrons only to artificial acceptors of high redox potential. The K _m for their specific substrates was about 1.0 mM for both enzymes, and their pH optimum was determined to be 7.5. For nicotinate dehydrogenase a content of 8.3 mol iron, 1.5 mol acid-labile sulfur, 2.0 mol flavin, and 1.5 mol molybdenum per mol of enzyme was determined. Both enzymes contained FAD and Fe/S center. After inhibition by KCN, thiocyanate was detected, and subsequently the initial nicotinate dehydrogenase activity was restored by the addition of Na₂S indicating the presence of cyanolyzable sulfur. 6-Hydroxynicotinate dehydrogenase seemed to contain the same type of constituents as determined for nicotinate dehydrogenase. A partial immunological identity of the enzymes could be shown by antibodies raised against nicotinate dehydrogenase.Abbreviations DCPIP 2,6-dichlorophenol-indophenol - EEO electroendosmosis - FTTC fluorescein isothiocyanate - HAP hydroxylapatite - 6-HDH 6-hydroxynicotinate dehydrogenase - NBT nitroblue tetrazolium chloride - NDH nicotinate dehydrogenase - MTT thiazolyl blue - PES phenazine ethosulfate - PMSF phenylmethyl sulfonyl fluoride - TEMED N,N,N',N'-tetramethyl-ethylenediamine     

Purification of the 2-oxoglutarate dehydrogenase and pyruvate dehydrogenase complexes of Neurospora crassa mitochondria

A simple purification procedure for the 2-oxoglutarate dehydrogenase and the pyruvate dehydrogenase complexes of Neurospora crassa mitochondria is described. After fractionated precipitations with polyethylene glycol, elimination of thiol proteins, and gel-filtration chromatography, the resulting preparations contained both activities. Covalent chromatography on thiol-activated Sepharose CL-4B allowed the specific binding of the 2-oxoglutarate dehydrogenase complex activity in the presence of 2-oxoglutarate, whereas the pyruvate dehydrogenase complex activity was retained in the presence of pyruvate. The purified 2-oxoglutarate dehydrogenase complex showed 4 protein bands by electrophoresis under dissociating conditions with apparent molecular weights of 160,000, 56,200, 55,600, 52,600 and a Km value of 3.8 X 10(-4) M for 2-oxoglutarate. The purified pyruvate dehydrogenase complex showed 5 protein bands with apparent molecular weights of 160,000, 57,600, 55,600, 52,500 and 37,100 and a Km value of 3.2 X 10(-4) M for pyruvate.     

Malate dehydrogenase and lactate dehydrogenase in trematodes and turbellarians

Studies have been made on the activity and properties of malate and lactate dehydrogenases from the cattle rumen trematodes Eurytrema pancreaticum, Calicophoron ijimai and the turbellarian Phagocata sibirica which has a common free-living ancestor with the trematodes. All the species studied have a highly active malate dehydrogenase, its activity in the reaction of reducing oxaloacetate being 6-14 times higher than in the reaction of malate oxidation. The affinity of malate dehydrogenase to oxaloacetate was found to be higher than that to malate. The activity of lactate dehydrogenase (reducing the pyruvate) was lower than the activity of malate dehydrogenase, the difference being 50 times for C. ijimai, 4 times for E. pancreaticum and 10 times for P. sibirica.     

Dark modulation of NADP-dependent malate dehydrogenase and glucose-6-phosphate dehydrogenase in the chloroplast

The properties of the system which reverses light modulation of NADP-dependent malate dehydrogenase and glucose-6-phosphate dehydrogenase activity in pea chloroplasts were examined. A factor catalyzing dark modulation of these enzymes was found. This factor cochromatographed with thioredoxin in all systems used (Sephacryl S-200, Sephadex G-75, DEAE-cellulose). Inhibition of dithiothreitol-dependent modulation and of dark reversal by antibody against Escherichia coli thioredoxin further suggest that the dark factor is in fact thioredoxin. It appears that the reaction is the reverse of the previously described dithiothreitol-dependent thioredoxin-catalyzed modulation of enzymes. The limiting step in vitro seems to be the oxidation of thioredoxin during the dark period.     

3 Alpha-hydroxysteroid dehydrogenase and 3 beta-hydroxysteroid dehydrogenase in the ovary of young Mongolian gerbils

The ovaries of sexually mature, pregnant mare serum gonadotropin (PMSG) stimulated, 12 week old Mongolian gerbils were investigated morphologically and enzyme histochemically for the appearance of the 3 alpha-hydroxy-steroid and the 3 beta-hydroxysteroid dehydrogenase during the estrous cycle. Up to ovulation, on day 3 of the estrous cycle, the number of vesicular follicles increases continuously. Primarily atretic follicles can be seen on day 4. On day 5 corpora lutea appear, but they degenerate already by day 6. During the entire estrous cycle, 3 alpha-hydroxysteroid dehydrogenase and 3 beta-hydroxysteroid dehydrogenase activity can be found in the theca of tertiary follicles and in the interstitial cells, whereas the theca of secondary follicles and the granulosa of healthy follicles do not exhibit any enzyme activity. The activity decreases from day 1 till day 6. The granulosa of atretic follicles and the cells of corpora lutea show only weak activity. It may be significant that the intensity of enzyme activity in the ovary and the estrogen level in the plasma are differently correlated to the estrous cycle.