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Biomedical subjects

C H Williams

Publications and source records attributed to C H Williams.

At least 109 records · Page 6Linked to original sources
PubMed1990

A new treatment for traumatic shock and ARDS.

Trauma causes more years of lost life than any other cause of death. Traumatic shock and sepsis are the most common late causes of death following trauma. Traumatic shock and sepsis cause multiple organ failure. The most common organ to fail is the lung, which develops Adult Respiratory Distress Syndrome (ARDS). ARDS can be caused by Disseminated Intravascular Coagulation (DIC) with microscopic clots in the lungs. Trauma causes hemolysis and the red cell stroma may initiate DIC. Plasminogen activators, which causes lysis of blood clot, can lyse pulmonary microthrombi and prevent the onset of ARDS even when given several hours after the trauma.

Animals↗
PubMed1990

Prevention of adult respiratory distress syndrome with plasminogen activator in pigs.

Death from traumatic shock has been associated with loss of blood externally or internally. However, many patients die after trauma, even though blood volume restoration is adequate. Death is often due to pulmonary failure (adult respiratory distress syndrome [ARDS]). Death and ARDS have been associated with disseminated intravascular coagulation (DIC) and microclots in the lungs. Dissolution of the microclots after trauma can be achieved by activation of endogenous plasmin. Nine pigs were anesthetized for 48 h. Trauma was administered by 60 standard blows to each thigh resulting in a bruise of muscle but no skin, bone, or major vessel injury. Nutrition and respiration were maintained at normal levels. All nine pigs died with severe lung pathology and low PaO2. Ten other traumatized pigs were treated with a plasminogen activator iv 4 h after trauma. Five of these were treated with tissue plasminogen activator (tPA) and five with urokinase. All treated pigs survived 48 h and maintained a normal PaO2. Autopsy showed minimal lung pathology.

Animals↗
PubMed1989

Lipoamide dehydrogenase from Escherichia coli. Steady-state kinetics of the physiological reaction.

Lipoamide dehydrogenase from Escherichia coli operates qualitatively by the same mechanism as the enzyme from pig heart. It has been suggested that quantitative differences between the two, in particular the marked inhibition of the bacterial enzyme by its product NADH, are related to the fact that the E. coli enzyme lacks the phosphorylation/dephosphorylation control present in the mammalian enzyme (Wilkinson, K. D., and Williams, C. H., Jr. (1981) J. Biol. Chem. 256, 2307-2314). Because of the inhibition by NADH, the kinetics of the E. coli enzyme have not been studied previously in the physiological direction with the natural substrate, dihydrolipoamide. We have now measured the steady-state kinetics of the oxidation of dihydrolipoamide by NAD+ using the stopped-flow technique to follow only the early time course. The pH dependence of kcat revealed an apparent pKa value of 6.7, reflecting ionization(s) of the enzyme-substrate complex. The pH dependence of kcat/Km gave an apparent pKa of 7.4 reflecting ionization(s) of the free 2-electron-reduced enzyme. The inhibition pattern for NADH was mixed, consistent with the fact that NADH is both a product inhibitor and inhibits by reducing a fraction of the enzyme to the catalytically inactive 4-electron-reduced state. There is a modest pH-dependent positive cooperativity in the saturation curve for NAD+ decreasing with increasing pH. Spectral changes in the 530 and 446 nm bands of the 2-electron-reduced enzyme, associated with the titration of the nascent thiols and the base, showed tentative pKa values of 6.4 and 7.1, respectively, in a pH jump experiment. The properties of the wild type E. coli enzyme can now be compared with those of several site-directed mutants.

Animals↗
PubMed1989

Titration studies on the active sites of pig heart lipoamide dehydrogenase and yeast glutathione reductase as monitored by the charge transfer absorbance.

Macroscopic pKa values associated with the influence of pH on the visible spectrum of 2-electron reduced pig heart lipoamide dehydrogenase and yeast glutathione reductase have been determined by monitoring changes in the principal flavin band near 460 nm and the charge transfer band at 540 nm. The ionization of at least three active site amino acid side chains can influence the spectra over the range of pH studied: the two nascent thiols (interchange thiol and electron transfer thiol) and the histidine residue which acts as the base catalyst in lipoamide dehydrogenase and the acid catalyst in glutathione reductase thiol-disulfide interchange reactions. These systems are analogous to, but more complex than, those in glyceraldehyde-3-phosphate dehydrogenase and papain where a single thiol and a histidine residue in a relatively apolar milieu form a thiolate-imidazolium ion pair which is favored over the thiol-imidazole prototropic tautomer. In an effort to more nearly mimic the papain titrations, the macroscopic pKa values were determined on reduced glutathione reductase which had been monoalkylated with iodoacetamide under conditions known to favor the reaction of the interchange thiol by at least 10 to 1 (Arscott, L. D., Thorpe, C., and Williams, C. H., Jr. (1981) Biochemistry 20, 1513-1520). Like papain and glyceraldehyde-3-phosphate dehydrogenase, alkylated glutathione reductase showed two macroscopic pKa values, at pH 3.7 and pH 9.1, and by analogy, these were associated primarily with the thiol and the imidazole, respectively. Results with the native enzymes depended on the wavelength monitored. Glutathione reductase had pKa values at 4.8, 7.1, and 9.2 when monitored at 540 nm and 5.1 and 8.2 when monitored at 462 nm. Lipoamide dehydrogenase had pKa values at 4.4 and 8.7 when monitored at 529 nm and 3.9, 7.0, and 9.3 when monitored at 455 nm.

Animals↗
PubMed1989

Inactivation-reactivation of two-electron reduced Escherichia coli glutathione reductase involving a dimer-monomer equilibrium.

Glutathione reductase from Escherichia coli is inactivated when incubated with either NADPH or NADH. The process is inversely dependent on the enzyme concentration. Inactivation is rapid and monophasic with 1 microM NADPH and 1 nM enzyme FAD giving a t1/2 of 1 min. Complex formation between NADPH and the two-electron reduced enzyme (EH2) at higher levels of NADPH protects against rapid inactivation. NADP+, produced in a side reaction with oxygen, also protects by forming a complex with EH2. These complexes make analysis of the concentration dependence of the inactivation process difficult. Inactivation with NADH, where complexes do not interfere, is slower but can be analyzed more readily. With 152 microM NADH and 5.4 nM enzyme FAD, the time required for 50% inactivation is 17 min. The process is markedly biphasic, reaching the final inactivation level after 5-7 h. Analysis of the relationship between the final level of inactivation with NADH and the enzyme concentration indicates that inactivation is due to dissociation of the normally dimeric enzyme. Thus, the position of the dimer-monomer equilibrium between an active dimeric two-electron reduced species and an inactive monomeric two-electron reduced form determines the enzyme activity. An apparent equilibrium constant (Kd) for dissociation of dimer obtained from the anaerobic concentration dependent inactivation curves is 220 nM. Enzyme inactivated with NADH can be reactivated with glutathione, and the reactivation kinetics are second order, monomer-monomer over 75% of the reaction with an average apparent association rate constant (ka) of 13.1 (+/- 5.5) X 10(6) M-1 min-1.

Enzyme Reactivators↗
PubMed1989

Characterization of two active site mutations of thioredoxin reductase from Escherichia coli.

Thioredoxin reductase (TRR), a member of the pyridine nucleotide-disulfide oxidoreductase family of flavoenzymes, undergoes two sequential thiol-disulfide interchange reactions with thioredoxin during catalysis. In order to assess the catalytic role of each nascent thiol of the active site disulfide of thioredoxin reductase, the 2 cysteines (Cys-136 and Cys-139) forming this disulfide have been individually changed to serines by site-directed mutageneses of the cloned trxB gene of Escherichia coli. Spectral analyses of TRR(Ser-136,Cys-139) as a function of pH and ionic strength have revealed two pKa values associated with the epsilon 456, one of which increases from 7.0 to 8.3 as the ionic strength is increased, and a second at 4.4 which is seen only at high ionic strength. epsilon 458 of wild type TRR(Cys-136,Cys-139) and epsilon 453 of TRR(Cys-136,Ser-139) are pH-independent. A charge transfer complex (epsilon 530 = 1300 M-1 cm-1), unique to TRR(Ser-136,Cys-139), has been observed under conditions of high ammonium cation concentration (apparent Kd = 54 microM) at pH 7.6. These results suggest the assignment of Cys-139 as the FAD-interacting thiol in the reduction of thioredoxin by NADPH via thioredoxin reductase. If, as with other members of this enzyme family, the two distinct catalytic functions are each carried out by a different nascent thiol, then Cys-136 would perform the initial thiol-disulfide interchange with thioredoxin. Steady state kinetic analyses of the proteins have revealed turnover numbers of 10 and 50% of the value of the wild type enzyme for TRR(Ser-136,Cys-139) and TRR(Cys-136,Ser-139), respectively, and no changes in the apparent Km values of TR(S2) or NADPH. The finding of activity in the mutants indicates that the remaining thiol can carry out interchange with the disulfide of thioredoxin, and the resulting mixed disulfide can be reduced by NADPH via the flavin.

Amino Acid Sequence↗
PubMed1989

Evidence for the participation of Cys558 and Cys559 at the active site of mercuric reductase.

Mercuric reductase, with FAD and a reducible disulfide at the active site, catalyzes the two-electron reduction of Hg(II) by NADPH. Addition of reducing equivalents rapidly produces a spectrally distinct EH2 form of the enzyme containing oxidized FAD and reduced active site thiols. Formation of EH2 has previously been reported to require only 2 electrons for reduction of the active site disulfide. We present results of anaerobic titrations of mercuric reductase with NADPH and dithionite showing that the equilibrium conversion of oxidized enzyme to EH2 actually requires 2 equiv of reducing agent or 4 electrons. Kinetic studies conducted both at 4 degrees C and at 25 degrees C indicate that reduction of the active site occurs rapidly, as previously reported [Sahlman, L., & Lindskog, S. (1983) Biochem. Biophys. Res. Commun. 117, 231-237]; this is followed by a slower reduction of another redox group via reaction with the active site. Thiol titrations of denatured Eox and EH2 enzyme forms show that an additional disulfide is the group in communication with the active site. [14C]Iodoacetamide labeling experiments demonstrate that the C-terminal residues, Cys558 and Cys559, are involved in this disulfide. The fluorescence, but not the absorbance, of the enzyme-bound FAD was found to be highly dependent on the redox state of the C-terminal thiols. Thus, Eox with Cys558 and Cys559 as thiols exhibits less than 50% of the fluorescence of Eox where these residues are present as a disulfide, indicating that the thiols remain intimately associated with the active site.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1988

Overexpression and mutagenesis of the lipoamide dehydrogenase of Escherichia coli.

A 'split-gene' technique for the overexpression and mutagenesis of the gene encoding the lipoamide dehydrogenase of Escherichia coli was developed in order to overcome the instability problems encountered when attempting to mutate the intact gene. The lipoamide dehydrogenase gene, lpd, was dissected into two fragments which were separately subcloned into M13 vectors for mutagenesis in vitro followed by reconstitution in the pJLA504 expression vector under the transcriptional control of the lambda PR and lambda PL promoters and a temperature-sensitive lambda repressor. After thermo-induction, E. coli cells transformed with the plasmid carrying the reconstituted lpd gene contained 4-5 times more lipoamide dehydrogenase activity than is normally found in the wild-type organism. The strategy was used to engineer a Glu-188----Asp replacement in lipoamide dehydrogenase, and this generated an enzyme with markedly different kinetic properties.

Cloning, Molecular↗
PubMed1988

Oxidation of 3-amino-1-phenylprop-1-enes by monoamine oxidase and their use in a continuous assay of the enzyme.

3-Amino-1-phenylprop-1-ene (cinnamylamine) and some derivatives were examined as substrates for monoamine oxidases A and B in mitochondria. All of the amines examined were readily oxidized by monoamine oxidase B but much less readily by monoamine oxidase A. E-Cinnamylamine was found to have Km 0.025 mM and Vmax. 3.9 nmol/min per mg of mitochondrial protein. Corresponding values with monoamine oxidase A were 0.026 mM and 0.85 nmol/min per mg respectively. Despite their different stereochemistry, E- and Z-N-methylcinnamylamines were almost equally effective as substrates for monoamine oxidase B. The characteristic u.v. absorbance and high absorption coefficient of cinnamaldehyde, the product produced by enzymic oxidation of cinnamylamine, is utilized in a sensitive continuous spectrophotometric assay for both enzymes in the rat and for the assay of a purified monoamine oxidase B from bovine liver.

Animals↗
PubMed1988

The kinetic mechanism of beef kidney D-aspartate oxidase.

The mechanism of action of the flavoprotein D-aspartate oxidase (EC 1.4.3.1) has been investigated by steady-state and stopped flow kinetic studies using D-aspartate and O2 as substrates in 50 mM KPi, 0.3 mM EDTA, pH 7.4, 4 degrees C. Steady-state results indicate that a ternary complex containing enzyme, O2, and substrate (or product) is an obligatory intermediate in catalysis. The kinetic parameters are turnover number = 11.1 s-1, Km(D-Asp) = 2.2 x 10(-3) M, Km(O2) = 1.7 x 10(-4) M. Rapid reaction studies show that 1) the reductive half reaction is essentially irreversible with a maximum rate of reduction of 180 s-1; 2) the free reduced enzyme cannot be the species which is reoxidized during turnover since its reoxidation by oxygen (second order rate constant equal to 5.3 x 10(2) M-1 s-1) is too slow to be of relevance in catalysis; 3) reduced enzyme can bind a ligand rapidly and be reoxidized as a complex at a rate faster than that observed for the free reduced enzyme; 4) the rate of reoxidation of reduced enzyme by oxygen during turnover is dependent on both O2 and D-aspartate concentrations (second order rate constant of reaction between O2 and reduced enzyme-substrate complex equal to 6.2 x 10(4) M-1 s-1); and 5) the rate-limiting step in catalysis occurs after reoxidation of the enzyme and before its reduction in the following turnover. A mechanism involving reduction of enzyme by substrate, dissociation of product from reduced enzyme, binding of a second molecule of substrate to the reduced enzyme, and reoxidation of the reduced enzyme-substrate complex is proposed for the enzyme-catalyzed oxidation of D-aspartate.

Amino Acid Oxidoreductases↗
PubMed1988

Detection of cytomegalovirus in shell vial cultures by using a DNA probe and early nuclear antigen monoclonal antibody.

An in situ biotinylated DNA probe assay was evaluated as an adjunct to anti-cytomegalovirus early nuclear antigen indirect immunofluorescence and cytopathic effect on cytomegalovirus-infected monolayers in shell vial cultures. Viral infection was detected by early nuclear antigen indirect immunofluorescence at 24 h and by DNA probe assay and shell vial cytopathic effect at 5 days.

Antibodies, Monoclonal↗
PubMed1987

D-aspartate oxidase from beef kidney. Purification and properties.

The flavoprotein D-aspartate oxidase (EC 1.4.3.1) has been purified to homogeneity from beef kidney cortex. The protein is a monomer with a molecular weight of 39,000 containing 1 molecule of flavin. The enzyme as isolated is a mixture of a major active form containing FAD and a minor inactive form containing 6-hydroxy-flavin adenine dinucleotide (6-OH-FAD). The absorption and fluorescence spectral properties of the two forms have been studied separately after reconstitution of the apoprotein with FAD or 6-OH-FAD, respectively. FAD-reconstituted D-aspartate oxidase has flavin fluorescence, shows characteristic spectral perturbation upon binding of the competitive inhibitor tartaric acid, is promptly reduced by D-aspartic acid under anaerobiosis, reacts with sulfite to form a reversible covalent adduct, stabilizes the red anionic form of the flavin semiquinone upon photoreduction, and yields the 3,4-dihydro-FAD-form after reduction with borohydride. A Kd of 5 X 10(-8) M was calculated for the binding of FAD to the apoprotein. 6-OH-FAD-reconstituted D-aspartate oxidase has no flavin fluorescence, shows no spectral perturbation in the presence of tartaric acid, is not reduced by D-aspartic acid under anaerobiosis, does not stabilize any semiquinone upon photoreduction, and does not yield the 3,4-dihydro-form of the coenzyme when reduced with borohydride; the enzyme stabilizes the p-quinoid anionic form of 6-OH-FAD and lowers its pKa more than two pH units below the value observed for the free flavin. The general properties of the enzyme thus resemble those of the dehydrogenase/oxidase class of flavoprotein, particularly those of the amino acid oxidases.

Amino Acid Oxidoreductases↗
PubMed1987

The behaviour of leucine aminopeptidase towards thionopeptides.

Thionoleucine S-anilide (Leut-anilide), Leut-Gly-OEt and Leut-Phe-OMe were synthesized and shown to be competitive inhibitors of leucine aminopeptidase from pig kidney. The kinetics of inhibition were determined in the presence of leucine 4-methylcoumarin-7-amide as substrate. Although the compounds showed only moderate inhibitory potency, it was found that all were resistant to hydrolysis by the enzyme, in contrast with the reported behaviour of some thionopeptide analogues of substrates for other Zn2+-peptidases such as carboxypeptidase A and angiotensin-converting enzyme.

Kinetics↗
PubMed1987

L-lactate-2-monooxygenase. Sequence of peptides containing residues modified by 1-fluoro-2,4-dinitrobenzene.

L-Lactate-2-monooxygenase (EC 1.13.12.4) inactivated by 1-fluoro-2,4-dinitrobenzene essentially as described previously (Choong, Y. S., Shepherd, M. G., and Sullivan, P. A. (1978) Biochem. J. 173, 255-262) incorporated 2.8 mol of the dinitrophenyl (DNP) moiety per mole of flavin. The inhibitors 2-methyl lactate or sulfite decreased the incorporation to 0.9 mol of DNP per mole of flavin. Peptide mapping by high performance liquid chromatography of radioactively labeled protein digested with trypsin showed three peaks of radioactivity. DNP-amino acid analysis and peptide sequencing showed that 2 distinct cysteine residues and a histidine residue had been modified. Both cysteine peptides were protected from modification by either of the inhibitors, whereas the histidine was only partially protected. The sum of the 2 cysteine peptides accounted for nearly 1 mole of label per mole of monomer. Since both of the cysteines are protected by inhibitors, they both must be in or near the substrate-binding site of the enzyme and appear to be modified in a mutually exclusive fashion. The histidine, on the other hand, does not lie directly in the substrate-binding site. It is possible that this histidine is the positively charged residue that is postulated to be near the N-1 position of the flavin.

Amino Acid Sequence↗
PubMed1987

Identification of methionine-110 as the residue covalently modified in the electrophilic inactivation of D-amino-acid oxidase by O-(2,4-dinitrophenyl) hydroxylamine.

The reaction of O-(2,4-dinitrophenyl)hydroxylamine with D-amino-acid oxidase leads to complete inactivation which can be protected against by the competitive inhibitor benzoate [D'Silva, C., Williams, C. H., Jr., & Massey, V. (1986) Biochemistry 25, 5602-5608]. The residue modified has been identified as methionine-110. Differential high-performance liquid chromatography mapping of tryptic digests of D-amino-acid oxidase modified in the absence and presence of benzoate allows the isolation of a single methionine-containing tryptic peptide corresponding to residues 100-115 and referred to as T6-T7. In unmodified enzyme, the bond involving Arg-108 is readily cleaved and T6 and T7 are isolated. Brief treatment of peptide T6-T7 with carboxypeptidase Y released residues 112-115, and the residual peptide was isolated in good yield. Further treatment of this peptide (residues 100-111) with carboxypeptidase Y released Val and an unknown amino acid that comigrated with synthetically prepared S-aminomethionine sulfonium salt. The unknown compound and S-aminomethionine break down to methionine on treatment with dithiothreitol.

Amino Acids↗