Bovine dihydropteridine reductase

Dihydropteridine reductase has been purified to homogeneity from bovine liver and bovine adrenal medulla by precipitation with polyethylene glycol, ion exchange chromatography, gel filtration, and affinity chromatography on 5-AMP-Sepharose 4B. The enzymes from the two tissues seem identical by the criteria of gel filtration chromatography, affinity chromatography, polyacrylamide gel electrophoresis in the presence and absence of dodecyl sulfate, isoelectric focusing, amino acid analysis, and binding of NADH. Fluorescence studies show two independent binding sites for NADH and a dissociation constant of 10 nM at pH 6.8. Isoelectric focusing of the enzyme as purified in the presence of NADH revealed three different bands, which by removal of this coenzyme were converted into a single band, corresponding to pI 5.7. The enzyme contains no carbohydrate or zinc.     

The effects of ionic strength on the self-association of human spectrin.

The self-association of human spectrin has been studied by means of sedimentation equilibrium in the analytical ultracentrifuge at pH 7.5 and over a range of ionic strength from 0.009 to 1.0 M. Increasing ionic strength above 0.1 M reduces the equilibrium constants for all of the measurable steps in the self-association reaction. These results support the concept of charge-charge interactions stabilizing the tetramer and higher oligomers with respect to the heterodimer. In addition, increasing ionic strength brought about a dissociation of the heterodimer to component polypeptide chains. Dissociation to the heterodimers is also enhanced with a decrease in ionic strength below 0.05 M. This low ionic strength-dependent dissociation is consistent with generalised electrostatic repulsion; however, this effect also correlates with some loss of alpha-helical content as revealed by circular dichroism. The secondary, tertiary and quaternary structures may all be partially disrupted by electrostatic free energy at low ionic strength.     

Characterization of Peptostreptococcus asaccharolyticus glutamate dehydrogenase purified by dye-ligand chromatography

Glutamate dehydrogenase (L-glutamate:NAD+ oxidoreductase (deaminating); EC 1.4.1.2) has been purified from Peptostreptococcus asaccharolyticus in a single step using dye-ligand chromatography. The enzyme (GDH) was present in high yields and was stabilized in crude extracts. A subunit molecular weight of 49000 +/- 500 was determined by SDS polyacrylamide gel electrophoresis and six bands were obtained after cross-linking the subunits with dimethyl suberimidate. This bacterial GDH was predominantly NAD+-linked, but was able to utilize both NADP+ and NADPH at 4% of the rates with NAD+ and NADH, respectively. An investigation of the amino acid specificity revealed some similarities with GDH from mammalian sources and some clear differences. The values of apparent Km for the substrates ammonia, 2-oxoglutarate, NADH, NAD+ and glutamate were 18.4, 0.82, 0.066, 0.031 and 6 mM, respectively. The P. asaccharolyticus GDH was not regulated by purine nucleotides, but was subject to strong inhibition with increasing ionic strength.     

Engineering surface charge. 1. A method for detecting subunit exchange in Escherichia coli glutathione reductase.

The gene gor encoding Escherichia coli glutathione reductase was mutated to create a positively charged N-terminal extension consisting of five arginine residues followed by a factor Xa cleavage site to the enzyme polypeptide chain. The modified protein assembled in vivo to yield a dimeric enzyme with kinetic parameters indistinguishable from those of wild-type glutathione reductase. The N-terminal extension could not be released by treatment with factor Xa but could be removed by exposure to trypsin, again without effect on the enzyme activity. The modified enzyme was readily separated from the wild-type enzyme by means of ion-exchange chromatography or nondenaturing polyacrylamide gel electrophoresis. Incubation of the modified and wild-type enzymes, separately or as a mixture, with NADH led to their partial inactivation, and activity was restored by exposure to 1 mM reduced glutathione. No hybrid dimer was formed in the mixture of modified and wild-type enzymes, as judged by polyacrylamide gel electrophoresis, strongly suggesting that the inactivation induced by NADH was not due to dissociation of the parental dimers. The addition of otherwise benign positively or negatively charged extensions to the N- or C-terminal regions of the constituent polypeptide chains of oligomeric enzymes offers a simple route to detecting hybrid formation and the causative subunit dissociation and exchange.     

A 220 kDa polypeptide, immunolocalized to epithelial tight junctions, is associated with brain clathrin preparations

Antibodies were raised in rabbits to highly purified preparations of bovine brain clathrin. The serum stained by immunofluorescence rat liver sections at tight junctions in a pattern that was identical to that previously reported (B. R. Stevenson et al.: J. Cell Biol. 103, 755-766 (1986] in which a monoclonal antibody specific to a 220 kDa (ZO-1) liver tight junction component was used. The serum also stained regions of the cell surface corresponding to the positions of intercellular junctions in confluent MDCK and HepG-2 cell cultures. Analysis of brain clathrin preparations resolved by polyacrylamide gel electrophoresis by immunoblotting with the serum indicated reaction with clathrin heavy and light chains as well as towards a 220 kDa polypeptide that was a minor component. Affinity purification of the serum provided antibodies directed mainly to clathrin light chains and these antibodies, as well as an independent antiserum to clathrin heavy chains, immunofluorescently stained liver tissue and cells in a manner typical of coated membranes/vesicles. These results suggested, by difference, that antibodies to a 220 kDa polypeptide, a minor constituent in brain clathrin preparations, were responsible for staining intercellular tight junctions in epithelia. The 220 kDa polypeptide present in brain clathrin preparations was demonstrated to be immunologically distinct from liver myosin heavy chain as well as erythrocyte and brain ankyrin. Comparison by two-dimensional mapping of the 220 kDa in brain clathrin with the clathrin heavy chain (180 kDa) polypeptide showed they were different proteins, but the 220 kDa polypeptide present in rat liver tight junctions was highly similar to the 220 kDa present in bovine brain clathrin preparations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histidine 454 plays an important role in polymerization of human glutamate dehydrogenase

Although previous chemical modification studies have suggested several residues to be involved in the maintenance of the quaternary structure of glutamate dehydrogenase (GDH), there are conflicting views for the polymerization process and no clear evidence has been reported yet. In the present study, cassette mutagenesis at seven putative positions (Lys333, Lys337, Lys344, Lys346, Ser445, Gly446, and His454) was performed using a synthetic human GDH gene to examine the polymerization process. Of the mutations at the seven different sites, only the mutagenesis at His454 results in depolymerization of the hexameric GDH into active trimers as determined by HPLC gel filtration analysis and native gradient polyacrylamide gel electrophoresis. The mutagenesis at His454 has no effects on expression or stability of the protein. The K_M values for NADH and 2-oxoglutarate were 1.5-fold and 2.5-fold greater, respectively, for the mutant GDH than for wild-type GDH, indicating that substitution at position 454 had appreciable effects on the affinity of the enzyme for both NADH and 2-oxoglutarate. The V_max values were similar for wild-type and mutant GDH. The k_cat/K_M value of the mutant GDH was reduced up to 2.8-fold. The decreased efficiency of the mutant, therefore, results from the increase in K_M values for NADH and 2-oxoglutarate. The results with cassette mutagenesis and HPLC gel filtration analysis suggest that His454 is involved in the polymerization process of human GDH.     

A soluble lipid.protein complex from bovine adrenal medulla chromaffin granules

A unique soluble lipoprotein has been isolated from aqueous lysates of bovine adrenal medulla chromaffin granules by DEAE-cellulose chromatography and gel filtration. Chloroform/methanol extracts of this complex contain sphingomyelin, lecithin, and cholesterol. Gel filtration in aqueous media indicate an approximate molecular weight of 900,000 for the complex. Incubation with sodium dodecyl sulfate causes dissociation to a low molecular weight polypeptide; prolonged treatment with guanidine HCl does not promote dissociation at all. Amino acid analysis revealed a high content of hydrophobic amino acids. Analysis of the tryptic fingerprint indicates that a single type of polypeptide chain is present. The complex appears to contain approximately five copies of polypeptide per aggregate.     

Characterization of specific interactions of coenzymes, regulatory nucleotides and cibacron blue with nucleotide binding domains of enzymes by analytical affinity chromatography

The dissociation constant for the complex of rhodanese and Cibacron Blue, determined by analytical affinity chromatography using rhodanese immobilized on controlled-pore glass (CPG) beads (200 nm pore diameter) and aminohexyl-Cibacron Blue, was 44 microM which agreed well with the kinetic inhibition constant, suggesting that the dye binds at or near the active site of this enzyme. Formation of a binary complex of the dye and lactate dehydrogenase (LDH) was also characterized by direct chromatography of LDH on CPG/immobilized Cibacron Blue (KD = 0.29 microM). The binary complex formed between LDH and NADH was characterized by analytical affinity chromatography using both CPG/immobilized LDH and immobilized Cibacron Blue. Since the dye competes with NADH in binding to the active site of LDH, competitive elution chromatography using the immobilized dye allows determination of the dissociation constant of the soluble LDH.NADH complex. Agreement between the dissociation constants determined by direct chromatography of NADH on immobilized LDH (KD = 1.4 microM) and that determined for the soluble complex (KD = 2.4 microM) indicates that immobilization of LDH did not affect the interaction. Formation of various binary, ternary and quaternary complexes of bovine liver glutamate dehydrogenase (GDH) with glutamate, NADPH, NADH, and ADP was also investigated using immobilized GDH. This approach allows characterization of the enzyme/ligand interactions without the complicating effect of enzyme self-association. The affinity for NADPH is considerably greater in the ternary complex (including glutamate) as compared to the binary complex (0.38 microM vs 22 microM); however, occupancy of the regulatory site by ADP greatly reduces the affinity in both complexes (6.4 microM and 43 microM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

3(17)beta-Hydroxysteroid Dehydrogenase of Pseudomonas testosteroni. Ligand binding properties.

The binding of NAD and NADH to electrophoretically pure 3(17)beta-hydroxysteroid dehydrogenase of Pseudomonas testosteroni was determined by Fluorescence spectroscopy and gel filtration. Four moles of cofactor are bound/mol of tetrameric enzyme; the binding sites are equivalent and independent. The dissociation constants for NAD and NADH are 16 and 0.25 micronM, respectively. As measured by gel filtration in the absence of cofactor, 0.4 mol of estradiol-17 beta is bound/mol of tetrameric enzyme. Data obtained from isotope exchange at equilibrium indicate that the binding of the cofactor to the enzyme is favored over the binding of steroid, although each may bind in the absence of the other. The rates of cofactor dissociation from the ternary complexes are slower than the rates of steroid dissociation; cofactor dissociation is probably the rate-limiting step. Cofactor analogs modified in the pyridine moiety are cosubstrates, whereas modified adenine derivatives are not. The enzyme also utilized as substrate a number of potential steroid affinity labels; no enzyme inactivation by these compounds was observed.     

Conditions for reciprocal conversion of oligomeric forms of heart mitochondrial creatine kinase

A procedure for purifying creatine kinase from bovine heart mitochondria, including enzyme extraction from mitochondria with salt solutions, concentration on cellulose phosphate gel and gel filtration on Sephacryl S-300 has been developed. Using ultracentrifugation in a sucrose density gradient and gel filtration, it was demonstrated that mitochondrial creatine kinase is present in solution as a mixture of two main forms, i. e., an octamer and a dimer. The distribution of the oligomeric forms is not influenced by changes in the ionic strength from 0.02 to 0.25, temperature (5-20 degrees C), freezing-thawing and the nature of monovalent anions (Cl-, NO3-, CH3COO-) and cations (Na+, K+) present in the medium. At pH 6.0, the predominant form is the octamer; an increase in pH induces its dissociation. An equilibrious mixture of the creatine kinase reaction substrates in the presence of Mg2+ also causes octamer dissociation; no dissociation is observed in the absence of Mg2+ or in the presence of one of the substrates. The non-working couple of substrates, Mg-ADP and creatine, causes dissociation of the octamer in the presence of Cl-, but not of CH3COO-. It is assumed that the dissociating effect of the substrates is due to conformational changes in the subunits concomitant with the formation of the creatine kinase active center in the course of catalysis. At physiological concentrations of nucleotide substrates, the degree of octamer dissociation depends on pH, creatine phosphate/creatine ratio and Pi. It is assumed that the above factors may regulate the reversible conversion of the octamer into the dimer in vivo.     

Purification of a bovine counterpart to human prealbumin and its interaction with a bovine retinol-binding protein

A bovine counterpart to human prealbumin was purified from bovine serum by thiol-disulfide exchange chromatography on thiol-Sepharose 4B and affinity chromatography on human retinol-binding protein linked to Sepharose 4B. The bovine prealbumin had alpha1-mobility on agarose gel electrophoresis at pH 8.6. It has the same molecular weight as human prealbumin on gel filtration and consisted of subunits with a molecular weight of 12 500. This is compatible with a tetrameric structure for the bovine protein. Antiserum against human prealbumin cross-reacted with bovine prealbumin and vice versa. The bovine prealbumin formed at high ionic strength complexes with another bovine serum protein which were dissociated at low ionic strength. This property was used to isolate a protein from bovine serum, by chromatography on bovine prealbumin linked to Sepharose which cross-reacted with antiserum against human retinol-binding protein; had a molecular weight of 21 000 and alpha 2-mobility on agarose gel electrophoresis. It was concluded that the latter protein was a bovine retinol-binding protein.     

Rat liver nuclear protein kinases NI and NII. Purification, subunit composition, substrate specificity, possible levels of regulation

Rat liver nuclear protein kinases NI and NII have been purified to homogeneity by an improved method. This method includes a casein-phosvitin-Sepharose column step, which separates the enzymes from the other chromosomal non-histone proteins, and a gel filtration at high ionic strength in the presence of a high concentration of protease inhibitors to separate the two enzymes from each other. NI has an apparent molecular mass of approximately 50 kDa and is composed of a single subunit. NII has an apparent molecular mass of 133 kDa and is composed of two subunits of identical molecular mass. The V and the Km of the two enzymes were determined for several substrates. Both enzymes phosphorylate chromosomal non-histone proteins with partly different specificities as shown by two-dimensional electrophoreses. When incubated in the absence of protease inhibitors, the enzymes were degraded into discrete polypeptides. Autophosphorylation of a polypeptide derived from NII was observed after incubation of the enzyme with ATP. This phosphorylation stimulated the enzyme activity. Several chromosomal proteins coeluted with NII from the casein-phosvitin-Sepharose column. They remained associated with the enzyme in sucrose gradients, during gel filtration performed at physiological ionic strength, and are dissociated at high ionic strength. These proteins were highly phosphorylated when the protein-NII complex was incubated with ATP.     

Equilibrium binding of nicotinamide nucleotides to lactate dehydrogenases

1. No discontinuities were observed during the continuous titration with NADH of the lactate dehydrogenases of ox muscle, pig heart, pig muscle, rabbit muscle, dogfish muscle or lobster tail muscle. The binding was monitored by either the enhanced fluorescence of bound NADH or the quenched fluorescence of the protein. A single macroscopic dissociation constant, independent of protein concentration, could be used to describe the binding to each enzyme, and there was no need to postulate the involvement of molecular relaxation effects. 2. The affinity for NADH decreases only threefold between pH6 and 8.5. Above pH9 the affinity decreases more rapidly with increasing pH and is consistent with a group of about pK9.5 facilitating binding. Muscle enzymes bind NADH more weakly than does the pig heart enzyme. 3. Increasing temperature and increasing concentrations of ethanol both weaken NADH binding. 4. NADH binding is weakened by increasing ionic strength. NaCl is more effective than similar ionic strengths derived from sodium phosphate or sodium pyrophosphate. 5. Commercial NAD(+) quenches the protein fluorescence of the heart and muscle isoenzymes. Highly purified NAD(+) does not, and its binding was monitored by competition for the NADH-binding sites. A single macroscopic dissociation constant is sufficient to describe NAD(+) binding at the concentrations tested. The dissociation constant is about 0.3mm and is not sensitive to changed ionic strength and to changed pH in the range pH6-8.5.     

Purification and Properties of Acetate Kinase from Acholeplasma laidlawii

Acetate kinase (EC 2.7.2.1) was purified from Acholeplasma laidlawii cytoplasm by a combination of ammonium sulfate fractionation, gel filtration, diethylaminoethyl-cellulose chromatography, and affinity chromatography on 8-(6-aminohexylamino)-adenosine 5'-triphosphate conjugated to Sepharose 4B. The enzyme was composed of polypeptide chains of about 50,000 molecular weight as estimated from sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Under nondenaturating conditions, apparent molecular weights between 64,000 and 130,000 were obtained, depending upon mainly the ionic strength of the test solution. The enzyme had a narrow specificity for phosphate acceptor acids, whereas both purine and pyrimidine nucleoside triphosphates were suitable phosphate donors. Na(+) and K(+) inhibited both acetyl phosphate and adenosine 5'-triphosphate synthesis, and the latter was also inhibited by high concentrations of adenosine 5'-diphosphate and acetyl phosphate. This substrate inhibition was partially abolished by 0.5 M NaCl. The enzyme catalyzed the independent adenosine 5'-diphosphate<-->adenosine 5'-triphosphate and acetate<-->acetyl phosphate exchanges. The rate of the latter was enhanced by the addition of cosubstrate Mg(2+)-adenosine 5'-triphosphate. The high affinity for substrates, except for acetate, indicated that under physiological conditions the direction of the enzymic reaction favors adenosine 5'-triphosphate synthesis. Thus, a mechanism for adenosine 5'-triphosphate generation in mycoplasmas is suggested.     

Purification and properties of low-Km aldehyde reductase from ox brain

A low-Km aldehyde reductase (alcohol:NADP+ oxidoreductase, EC 1.1.1.2), which may be identical with aldose reductase (alditol:NADP+ 1-oxidoreductase, EC 1.1.1.21), has been purified from ox brain to homogeneity. It was shown to be a monomer with Mr values of 31 000 and 35 100 being obtained by gel filtration and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate, respectively. The enzyme catalyses the NADPH-dependent reduction of a number of aromatic and sugar aldehydes. The activity of the enzyme with 133 microM NADH was about one-third of that with 120 microM NADPH. Activity with both these coenzymes was optimum at pH 6.2 and was inhibited by increasing the ionic strength with KCl, NaCl or NaNO3. In contrast, the activity was stimulated by sodium phosphate. The activity with NADH as the coenzyme was more sensitive to stimulation by phosphate and to inhibition by increasing ionic strength than that determined with NADPH.     

Steady-state and pre-steady-state kinetics of propionaldehyde oxidation by sheep liver cytosolic aldehyde dehydrogenase at pH 5.2. Evidence that the release of NADH remains rate-limiting in the enzyme mechanism at acid pH values

The kcat value for the oxidation of propionaldehyde by sheep liver cytosolic aldehyde dehydrogenase increased 3-fold, from 0.16 s-1 at pH 7.6 to 0.49 s-1 at pH 5.2, in parallel with the increase in the rate of displacement of NADH from binary enzyme.NADH complexes. A burst in nucleotide fluorescence was observed at all pH values consistent with the rate of isomerization of binary enzyme.NADH complexes constituting the rate-limiting step in the steady state. No substrate activation by propionaldehyde was observed at pH 5.2, but the enzyme exhibited dissociation/association behavior. The inactive dissociated form of the enzyme was favored by low enzyme concentration, low pH, and low ionic strength. Propionaldehyde protected the enzyme against dissociation.     

Kinetic and physical properties of the L-malate-NAD+ oxidoreductase from Methanospirillum hungatii and comparison with the enzyme from other sources.

The L-malate-NAD+ oxidoreductase of Methanospirillum hungatii was purified to homogeneity by using Blue Sepharose and ADP-Sepharose affinity chromatography. The molecular weight was estimated as 61 700 +/- 1900 by gel filtration and 64 200 +/- 1200 by ultracentrifugation. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis indicated that the protein is composed of two polypeptide chains, each corresponding to 31 350 +/- 2150 daltons. Inhibition patterns obtained for malate, alpha-oxoglutarate and ADP established that the sequential reaction mechanism was ordered, with NADH serving as the first substrate. Intracellular concentrations of oxaloacetate approximated the Km value of 27 microM, but NADH was present at less than Km values. Comparison of the amino-acid composition of the L-malate-NAD+ oxidoreductase of M. hungatii and 22 others from prokaryotic and eukaryotic cells revealed a significant direct relationship between average hydrophobicity and the frequency of non-polar side chains, as well as a significant indirect relationship between average hydrophobicity and the polarity ratio. Calculations based on amino-acid-composition data indicated significant composition similarity between pairs of mammalian-cytoplasmic or pairs of mitochondrial L-malate-NAD+ oxidoreductases from various sources, but no significant composition similarity between any of the pairs of bacterial species examined.     

The interconversion between monomeric and dimeric bovine heart cytochrome c oxidase

Monomers and dimers of bovine heart cytochrome c oxidase (EC 1.9.3.1.) were separated by gel filtration chromatography on Ultrogel AcA 34 or by sucrose gradient centrifugation. Factors influencing the interconversion of the two aggregation states of this enzyme were analyzed. At very low ionic strength, in the presence of dodecyl maltoside, monomers were the main species. Salts appeared to stabilize the dimeric form, divalent cations being more efficient than monovalent. High enzyme concentrations favoured the formation of dimers, also at low ionic strength. The type of detergent had a strong influence on the monomer-dimer interconversion; in Triton X-100 and dodecyl maltoside (at high ionic strength) cytochrome c oxidase was homogenously dispersed in its dimeric form, while in Tween-80 gel filtration showed only large particles eluting in the void volume. In cholate monomers and aggregates were observed but no dimers. The aggregation state had an influence on the steady state kinetics of the ferrocytochrome c oxidase activity. Monomers showed linear Eadie-Hofstee plots, whilst the dimeric and aggregated enzyme gave nonlinear Eadie-Hofstee plots. Ionic strength, enzyme concentration and type of detergent were affecting the enzyme's kinetics in a way consistent with the molecular form obtained by the gel filtration or sedimentation analysis. The data support a negative cooperative mechanism for the interaction of cytochrome c with the dimeric enzyme, as proposed earlier (K.A. Na?ecz et al., (1983) Biochem. Biophys. Res. Commun., 114, 822-828).     

Argininosuccinase from bovine brain: isolation and comparison of catalytic, physical, and chemical properties with the enzymes from liver and kidney.

Homogeneous argininosuccinase has been isolated from bovine brain: compared to liver and kidney argininosuccinases from the same species, the catalytic activity (1400 U/mg). molecular weight of the fully active form (202,000 by gel filtration), and the minimum molecular weight (50, 000 in sodium dodecyl sulfate and mercaptoethanol) were in agreement with published liver and kidney enzyme values from this laboratory. That the brain enzyme is composed of four identical, or closely similar, polypeptide chains is supported by peptide maps analyzed after tryptic or cyanogen bromide cleavage. One-fourth the number of peptide fragments were produced as compared to the total number of susceptible residues per mole. The number of peptides containing other specific residues, or methionyl residues, were consistently one-fourth of the total considered. As maps of peptide fragments prepared from the brain enzyme were also superimposable, or nearly so, on liver enzyme maps, the four polypeptide chains from both sources were closely similar to each other in amino acid sequence. Distribution of the 16 sulfhydryl groups, as based on titration with Ellman's reagent, was in accord with the liver enzyme: Four sulfhydryl groups reacted without affecting catalytic activity, a second group of 4 became accessible on cold dissociation of the tetramers to catalytically inactive dimers, and the final 8 became accessible in strong dissociating agents. On analysis, K_m values and negative homotropic interactions with substrate were in accord with liver enzyme kinetics. Immunological studies indicated a ciose resemblance in antigenic properties. The brain enzyme, as antigen, was fully crossreactive in the formation of precipitin bands with rabbit antibody to either liver or kidney enzymes already known to be mutually cross-reactive. The antibody to the liver enzyme was an effective inhibitor of brain enzyme activity comparable to inhibition of the homologous liver and kidney antigen.