Purification and molecular and enzymic properties of mitochondrial NADH dehydrogenase.

Mitochondrial NADH dehydrogenase has been purified to homogeneity by resolution of Complex I from beef heart mitochondria with the chaotrope NaClO₄ and precipitation of the enzyme with ammonium sulfate. The enzyme is water-soluble, has a molecular weight of 69,000 ± 1000 as determined by gel filtration on Sephadex G-100 and agarose 1.5 M. It is an iron-sulfur flavoprotein, with the ratio of flavin (FMN) to nonheme iron to labile sulfide being 1:5–6:5–6. The FMN content suggests a minimum molecular weight of 74,000 ± 3000 for the enzyme. NADH dehydrogenase is composed of three subunits with apparent M_r values, as determined by acrylamide gel electrophoresis as well as by gel filtration on agarose 5 M both in the presence of sodium dodecyl sulfate, of about 51,000, 24,000, and 9–10,000. Coomassie blue stain intensities of the subunits on acrylamide gels suggest that they are present in NADH dehydrogenase in equimolar amounts. However, summation of the apparent M_r values of the dodecyl sulfate-treated subunits appears to overestimate the molecular weight of the native enzyme. The amino acid compositions of NADH dehydrogenase and of each of the isolated and purified subunits have been determined. NADH dehydrogenase catalyzes the oxidation of NADH and NADPH by quinones, ferric compounds, and NAD (3-acetylpyridine adenine dinucleotide was used). All the activities of NADH dehydrogenase are greatly stimulated by addition of guanidine (up to 150 mm), alkylguanidines, arginine, and arginine methyl ester to the assay medium. Phosphoarginine had no effect. These results pointed to the importance of the positively charged guanido group, which appears to interact with and neutralize the negative charges on NAD(P)H and thereby allow for better enzyme-substrate interaction. In the absence of guanidine, NADPH is essentially unoxidized by the enzyme at pH values above 6.0. However, both NADPH dehydrogenase and NADPH → NAD transhydrogenase activities increase dramatically as the assay pH is lowered below pH = 6. Since the pK of the 2′-phosphate of NADPH is 6.1, it appears that the above pH effect is related to protonation of the 2′-phosphate, thus rendering NADPH a closer electronic analog of NADH, which is the primary substrate of the enzyme.     

Purification and properties of pyruvate dehydrogenase kinase from bovine kidney

Pyruvate dehydrogenase kinase was purified about 2,700-fold to apparent homogeneity from extracts of bovine kidney mitochondria. The kinase consists of two subunits (alpha beta) with molecular weights of 48,000 (alpha) and 45,000 (beta) as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Kinase activity resides in the alpha subunit. The alpha subunit is sensitive to proteolysis by chymotrypsin, whereas the beta subunit is selectively modified by trypsin. These observations, together with the results of peptide mapping, indicate that the two subunits are distinctly different proteins. It is proposed that the beta subunit is a regulatory subunit.     

A menadione-stimulated pyridine nucleotide oxidase from resting bovine neutrophil membranes. Purification, properties, and immunochemical cross-reactivity with the human neutrophil NADPH oxidase

A menadione-stimulated, superoxide-generating enzyme was purified 127-fold from resting bovine polymorphonuclear leukocyte (neutrophil) membranes with a yield of 34%. The enzyme was extracted with Triton X-100 and purified by chromatography on DEAE-Sepharose CL-6B, NAD-agarose, and Sephacryl S-200. The purified enzyme contained FAD and had an apparent molecular mass of 93 kDa by sodium dodecyl sulfate gel electrophoresis. In a nondenaturing gel electrophoresis system, the enzyme was multimeric (Mr greater than 400,000). The oxidase showed 3-4-fold higher activity (Vm) with NADH compared with NADPH, but the Km for both pyridine nucleotides was similar (39 and 47 microM, respectively). The enzyme transferred electrons to cytochrome c, dichlorophenolindophenol, and nitro blue tetrazolium. Cytochrome c reduction was stimulated 4-fold by menadione and was inhibited 70% by superoxide dismutase. Cytochrome c reduction was not inhibited by several mitochondrial respiratory chain inhibitors (azide, cyanide, and rotenone) but was sensitive to thiol-reactive agents (p-chloromercuribenzoate and monoiodo acetate). The catalytic properties of this enzyme distinguish it from the NADPH-dependent superoxide-generating respiratory burst oxidase (NADPH-oxidase) of human neutrophils. Nevertheless, antibodies to this enzyme inhibited not only the purified menadione-stimulated oxidase, but also the respiratory burst oxidase in membranes isolated from activated human neutrophils, indicating similar antigenic determinants are shared by these enzymes. Western blots of human neutrophil membranes visualized a plasma membrane protein of molecular mass 67 kDa, corresponding in size to a protein previously reported in preparations of the human respiratory burst oxidase.     

Chemical cross-linking of mitochondrial NADH dehydrogenase from bovine heart.

The structure of bovine heart mitochondrial NADH dehydrogenase was investigated by using two cleavable cross-linking agents, disuccinimidyl tartrate and (ethylene glycol)yl bis-(succinimidyl succinate). Cross-linking was analysed primarily by immunoblotting to detect products containing subunits of the iron-protein fraction from chaotropic resolution of the enzyme, namely those of 75, 49, 30 and 13 kDa. By using both the isolated iron-protein fraction and the intact dehydrogenase, cross-links were identified between these four subunits, from these subunits to the largest subunit of the flavoprotein fraction, which contains the active site for NADH, and from these subunits to polypeptides in the hydrophobic shell, which surrounds the hydrophilic iron-protein and flavoprotein fractions.     

Purification and properties of NADH dehydrogenase from a thermoacidophilic archaebacterium, Sulfolobus acidocaldarius

An NADH dehydrogenase was purified to electrophoretical homogeneity from Sulfolobus acidocaldarius, a thermoacidophilic archaebacterium optimally growing at pH 2-3 and 75 degrees C. A 2,100-fold purification was achieved. The purified enzyme is an acidic protein with an isoelectric point of 5.6 and a molecular weight of 95,000, consisting of two 50,000-dalton subunits. The enzyme showed an absorption spectrum characteristic of flavoproteins, with maxima at 272, 372, and 448 nm. The enzyme is highly thermostable, is specific for NADH as an electron donor, and is capable of using 2,6-dichlorophenolindophenol, ferricyanide, benzoquinone, and naphthoquinone as electron acceptors. Though at a low rate, caldariellaquinone, a unique and sole benzothiophenequinone in the genus Sulfolobus, was also reduced by the enzyme, suggesting that the enzyme is a possible member of the respiratory chain of the thermoacidophilic archaebacterium.     

Purification and characterization of NADH dehydrogenase from Bacillus subtilis

NADH dehydrogenase from Bacillus subtilis W23 has been isolated from membrane vesicles solubilized with 0.1% Triton X-100 by hydrophobic interaction chromatography on an octyl-Sepharose CL-4B column. A 70-fold purification is achieved. No other components could be detected with sodium dodecyl sulphate polyacrylamide gel electrophoresis. Ferguson plots of the purified protein indicated no anomalous binding of sodium dodecyl sulphate and an accurate molecular weight of 63 000 could be determined. From the amino acid composition a polarity of 43.8% was calculated indicating that the protein is not very hydrophobic. Optical absorption spectra and acid extraction of the enzyme chromophore followed by thin-layer chromatography showed that the enzyme contains 1 molecule FAD/molecule. The enzyme was found to be specific for NADH. NADPH is oxidized at a rate which is less than 6% of the rate of NADH oxidation. The activity of the enzyme as determined by NADH:3-(4'-5'-dimethyl-thiazol-2-yl)2,4-diphenyltetrazolium bromide oxidoreduction is optimal at 37 C and pH 7.5-8.0. The purified enzyme has a Kapp for NADH of 60 microM and a V of 23.5 mumol NADH/min X mg protein. These parameters are not influenced by phospholipids. The enzyme activity is hardly or not at all affected by NADH-related compounds such as ATP, ADP, AMP, adenosine, deoxyadenosine, adenine and nicotinic amide indicating the high binding specificity of the enzyme for NADH.     

Purification and properties of pyruvate dehydrogenase phosphatase from bovine heart and kidney

Pyruvate dehydrogenase phosphatase was purified to apparent homogeneity from bovine heart and kidney mitochondria. The phosphatase has a sedimentation coefficient (S20,w) of about 7.4 S and a molecular weight (Mr) of about 150 000 as determined by sedimentation equilibrium and by gel-permeation chromatography. The phosphatase consists of two subunits with molecular weights of about 97 000 and 50 000 as estimated by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. Phosphatase activity resides in the Mr 50 000 subunit, which is sensitive to proteolysis. The phosphatase contains approximately 1 mol of flavin adenine dinucleotide (FAD) per mol of protein of Mr 150 000. FAD is apparently associated with the Mr 97 000 subunit. The function of this subunit remains to be established. The phosphatase binds 1 mol of Ca2+ per mol of enzyme of Mr 150 000 at pH 7.0, with a dissociation constant (Kd) of about 35 microM as determined by flow dialysis. Use of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetate (EGTA) at pH 7.6 in conjunction with flow dialysis gave a Kd value for Ca2+ of about 8 microM. In the presence of both the phosphatase and the dihydrolipoyl transacetylase (E2) core of the pyruvate dehydrogenase complex, two equivalent and apparently non-interacting CA2+-binding sites were detected per unit of Mr 150 000, with a Kd value of about 24 microM in the absence and about 5 microM in the presence of EGTA. In the presence of 0.2 M KCl, which inhibits phosphatase activity about 95%, the phosphatase exhibited only one Ca2+-binding site, even in the presence of E2. The phosphatase apparently possesses an "intrinsic" Ca2+-binding site, and a second Ca2+-binding site is produced in the presence of E2. The second site is apparently altered by increasing the ionic strength. It is proposed that the second site may be at the interface between the phosphatase and E2, with Ca2+ acting as a bridging ligand for specific attachment of the phosphatase to E2.     

Purification and kinetic properties of 3 beta-hydroxysteroid dehydrogenase from bovine adrenocortical microsomes

3 beta-Hydroxysteroid dehydrogenase was purified from bovine adrenocortical microsomes and its properties were studied. The purified dehydrogenase gave a single homogeneous protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and showed no steroid delta 5-delta-4 isomerase activity. The molecular weight of the dehydrogenase was estimated to be 41,000 for the monomer and the isoelectric point was determined to be at pH 6.3. The Km values of the dehydrogenase were 6.2 microM for NAD+, 4.9 mM for NADP+, 2.0 microM for pregnenolone, and 5.3 microM for 17 alpha-hydroxypregnenolone. The mechanism of inhibition by trilostane of the dehydrogenase was also examined kinetically. The inhibition was found to be competitive, with Ki values of 0.14 microM for 17 alpha-hydroxypregnenolone and 0.38 microM for pregnenolone.     

Purification and properties of NADP-specific malate dehydrogenase from bovine adrenal cortex mitochondria

An electrophoretically homogeneous preparation of mitochondrial NADP-dependent malate dehydrogenase with a specific activity of 155 u./mg and a 67% yield has been obtained, using ammonium sulfate fractionation, gel filtration through Toyopearl HW-55 F, ion-exchange chromatography on DEAE-Toyopearl 650 M and affinity chromatography on 2',5'-ADP-Sepharose 4B. The molecular mass of native malate dehydrogenase is 260 kD; Mr of the SDS-treated enzyme is 61 kD, which is suggestive of a tetrameric structure of the protein. Malate dehydrogenase is active only in the presence of Mg2+ or Mn2+, but not Ca2+ or Ba2+. The Km' values for Mn2+ and Mg2+ are 50 and 66 microM, respectively. At low malate concentrations and NADP saturation, the enzyme is characterized by a sigmoidal kinetics which changes to hyperbolic at low concentrations of NADP. The Lineweaver--Burk plots for the dependence of the initial reaction rate on the concentration of one substrate at several fixed concentrations of the other substrate intersect to the left of the B-axis. NADPH competes with NADP:pyruvate inhibits malate dehydrogenase ++noncompetitively with respect to the coenzyme. NADPH and pyruvate inhibit the malate dehydrogenase-catalyzed reaction via a mixed type mechanism with respect to malate. The data obtained are consistent with a consecutive mechanism of reaction, whose first substrate is NADP and the last product is NADPH.     

Purification and properties of NADP-dependent isocitrate dehydrogenase from the bovine adrenal cortex

NADP-dependent isocitrate dehydrogenase (EC 1.1.42) was isolated and 430 times purified from the hyaloplasm fraction of bull adrenal cortex using fractionation by ammonium sulphate and acetone, heat treatment, chromatography on DEAE-Sephadex A-50, gel-filtration on Sephadex G-200 and affinity chromatography on 2',5'-ADP-sepharose 4B. The specific activity of homogeneous enzyme is 60 units per 1 mg of protein at 30 degrees C, yield--34%, pH optimum--8.0, molecular weight, determined by gel filtration on Sephadex G-200, is 96 kDa. The preparation electrophoresis in PAAG in the presence of DS-Na reveals one protein fraction with the mobility corresponding to that of protein having molecular weight of 46 kDa. The data obtained evidence for a dimer structure of the isocitrate dehydrogenase molecule from bull adrenals.     

Purification and properties of branched-chain alpha-keto acid dehydrogenase kinase from bovine kidney

Branched-chain alpha-keto acid dehydrogenase (BCKDH) kinase was purified 5000-fold to apparent homogeneity from extracts of bovine kidney mitochondria. The kinase co-purified with the BCKDH complex. About 70% of the kinase was released by treatment of the complex with 1.5 M NaCl and 0.1% 2-mercaptoethanol at pH 7.4, followed by chromatography on Sephacryl S-400. The uncomplexed kinase was purified further by chromatography on Q Sepharose and Superose 12. The purified kinase is a monomer of apparent Mr approximately 43,000. BCKDH kinase exhibited little activity, if any, toward pyruvate dehydrogenase.     

NADH dehydrogenase of Corynebacterium glutamicum. Purification of an NADH dehydrogenase II homolog able to oxidize NADPH

NADPH oxidase activity, in addition to NADH oxidase activity, has been shown to be present in the respiratory chain of Corynebacterium glutamicum. In this study, we tried to purify NADPH oxidase and NADH dehydrogenase activities from the membranes of C. glutamicum. Both the enzyme activities were simultaneously purified in the same fraction, and the purified enzyme was shown to be a single polypeptide of 55 kDa. The N-terminal sequence of the enzyme was consistent with the sequence deduced from the NADH dehydrogenase gene of C. glutamicum, which has been sequenced and shown to be a homolog of NADH dehydrogenase II. In addition to high NADH-ubiquinone-1 oxidoreductase activity at neutral pH, the purified enzyme showed relatively high NADPH oxidase and NADPH-ubiquinone-1 oxidoreductase activities at acidic pH. Thus, NADH dehydrogenase of C. glutamicum was shown to be rather unique in having a relatively high reactivity toward NADPH.     

Arogenate dehydrogenase from Streptomyces phaeochromogenes. Purification and properties

Arogenate dehydrogenase, the terminal enzyme of tyrosine biosynthesis in Streptomyces phaeochromogenes, was purified to homogeneity by a five-step procedure. The enzyme is a dimer of Mr 57 600 as determined by dodecyl sulfate polyacrylamide gel electrophoresis after cross-linking of the monomers, or of 66 300 as found by gel permeation chromatography, and consists of two identical subunits of Mr 28 100. The pI of the enzyme is 4.45, and the Km values are 0.105mM for arogenate and 0.01 mM for NAD.     

Purification and properties of the bovine liver mitochondrial dihydroorotate dehydrogenase

Dihydroorotate dehydrogenase has been purified 6,000-fold from bovine liver mitochondria to apparent homogeneity in six steps. Electrophoretic migration of the homogeneous enzyme on sodium dodecyl sulfate-polyacrylamide gels reveals a subunit Mr of 42,000. By contrast to the well-characterized, cytosolic dihydroorotate oxidases (EC 1.3.3.1), the purified bovine dehydrogenase is a dihydroorotate:ubiquinone oxidoreductase. Maximal rates of orotate formation are obtained using coenzymes Q6 or Q7 as cosubstrate electron acceptors. Concomitant with substrate oxidation, the enzyme will reduce simple quinones, such as benzoquinone, but at significantly lower rates (10-15%) than that obtained for reduction of coenzyme Q6. Enzyme-catalyzed substrate oxidation is not supported by molecular oxygen. The specificity of the purified enzyme for dihydropyrimidine substrates has also been explored. The methyl-, ethyl-, t-butyl-, and benzyl-S-dihydroorotates are substrates, but 1- and 3-methyl and 1,3-dimethyl methyl-S-dihydroorotates are not. Competitive inhibitors include product orotate, 5-methyl orotate, and racemic cis-5-methyl dihydroorotate.     

Alanine dehydrogenase from Streptomyces fradiae. Purification and properties

Alanine dehydrogenase was purified to homogeneity from a cell-free extract of Streptomyces fradiae, which produces tylosin. The enzyme was purified 1180-fold to give a 21% yield, using a combination of hydrophobic chromatography and ion-exchange fast protein liquid chromatography. The relative molecular mass of the native enzyme was determined to be 210,000 or 205,000 by equilibrium ultracentrifugation or gel filtration, respectively. The enzyme is composed of four subunits, each of Mr 51,000. Using analytical isoelectric focusing the isoelectric point of alanine dehydrogenase was found to be 6.1. The Km were 10.0 mM for L-alanine and 0.18 mM for NAD+. Km values for reductive amination were 0.23 mM for pyruvate, 11.6 mM for NH4+ and 0.05 mM for NADH. Oxidative deamination of L-alanine proceeds through a sequential-ordered binary-ternary mechanism in which NAD+ binds first to the enzyme, followed by alanine, and products are released in the order ammonia, pyruvate and NADH.     

Purification and properties of NADH oxidase from Bacillus megaterium

NADH oxidase, which catalyzes the oxidation of NADH, with the consumption of a stoichiometric amount of oxygen, to NAD+ and hydrogen peroxide was purified from Bacillus megaterium by 5'-AMP Sepharose affinity chromatography to homogeneity. The enzyme is a dimeric protein containing 1 mol of FAD per mol of subunit, Mr = 52,000. The absorption maxima of the native enzyme (oxidized form) were found at 270, 383, and 450 with a shoulder at 475 nm in 50 mM KPi buffer, pH 7.0. The visible absorption bands at 383 and 450 nm disappeared on the addition of NADH under anaerobic conditions and reappeared upon the introduction of air. Thus, the non-covalently bound FAD functioned as a prosthetic group for the enzyme. We tentatively named this new enzyme NADH oxidase (NADH:oxygen oxidoreductase, hydrogen peroxide forming). This enzyme stereospecifically oxidizes the pro-S hydrogen at C-4 of the pyridine ring of NADH.