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C H Williams

Publications and source records attributed to C H Williams.

At least 181 records · Page 10Linked to original sources
PubMed1976

Measurement of the oxidation-reduction potentials for two-electron and four-electron reduction of lipoamide dehydrogenase from pig heart.

The oxidation-reduction potential, E2, for the couple oxidized lipoamide dehydrogenase/2-electron reduced lipoamide dehydrogenase has been determined by measurement of equilibria of these enzyme species with lipoamide and dihydrolipoamide or with oxidized and reduced azine dyes. E2 is -0.280 V at pH 7, and deltaE2/deltapH is -0.06 V in the pH range 5.5 to 7.6. Values for E1, the oxidation-reduction potential for the couple 2-electron reduced enzyme/4-electron reduced enzyme, were obtained from measurements of the extent of dismutation of 2-electron reduced enzyme to form mixtures containing oxidized and 4-electron reduced enzyme. E1 is -0.346 V at pH 7, and deltaE1/deltapH is -0.06 V in the pH range 5.7 to 7.6. Spectra of oxidized enzyme and 4-electron reduced enzyme do not show variations with pH over this range, but the spectrum of the 2-electron reduced enzyme is pH-dependent, with the molar extinction at 530 nm changing from 3250 M-1 cm-1 at pH 8 to 2050 M-1 cm-1 at pH 5.2. The pH-dependent changes which are observed in the absorption properties of the 2-electron reduced enzyme are consistent with the disappearance of a charge transfer complex between an amino acid side chain and the oxidized flavin at the lower pH values, with the apparent pK of the side chain at pH 5. It has been suggested that the 530 nm absorbance of 2-electron reduced enzyme is due to a charge transfer complex between thiolate anion and oxidized flavin, and we propose that the thiolate anion is stabilized by interaction with a protonated base. The thermodynamic data predict that the amount of 4-electron reduced enzyme formed when the enzyme is reduced by excess NADH will be pH-dependent, with the greatest amounts seen at low pH values. These data support earlier evidence (Matthews, R.G., Wilkinson, K.D., Ballou, D,P., and Williams, C.H., Jr. (1976) in Flavins and Flavoproteins (Singer, T.P., ed) pp. 464-472; Elsevier Scientific Publishing Co., Amsterdam) that the role of NAD+ in the NADH-lipoamide reductase reaction catalyzed by lipoamide dehydrogenase is to prevent accumulation of inactive 4-electron reduced enzyme by simple reversal of the reduction of 2-electron reduced enzyme by NADH.

Animals↗
PubMed1976

Differential reactivity of the two active site cysteine residues generated on reduction of pig heart lipoamide dehydrogenase.

Reduction of the active center disulfide bond in the flavoprotein pig heart lipoamide dehydrogenase generates two sulfur moieties which are chemically inequivalent in the 2-electron reduced form of the enzyme. Thus 1 cysteine residue is at least 13-fold more reactive than its partner toward iodoacetamide at pH 7.6. This selectivity was demonstrated by reaction of the 2-electron reduced enzyme with a low concentration of iodo[1-14C]acetamide under anaerobic conditions. The formation of a monolabeled derivative is accompanied by the reappearance of a spectrum of oxidized bound flavin, clearly different from that of the native enzyme. Alkylation of the remaining cysteine residues with iodo[12C]acetamide enabled the isolation of a tryptic version of the active center disulfide peptide. A single chymotryptic cleavage between the 2 alkylated cysteine residues generated a cationic and an anionic fragment containing 7% and 93% of the radioactivity of the purified tryptic peptide, respectively. The monolabeled derivative is catalytically inactive toward reduced or oxidized lipoamide, but is approximately 2-fold better as a transhydrogenase than the native protein using NADH and acetylpyridine adenine dinucleotide as substrates. Anaerobic titration with NADH leads to reduction of the flavin with concomitant formation of long wavelength absorption of low intensity. No intermediate reduced states were detected in this titration analogous to the red 2-electron form observed with the native enzyme. Similarly, intermediates during reduction of the enzyme by 1 eq of dithionite have not been detected.

Anaerobiosis↗
PubMed1976

The chronically reserpinized rat as a possible animal model for cystic fibrosis. IV. The protein composition of pulmonary lavage fluid.

Lung lavage samples obtained from patients with cystic fibrosis (CF) had significantly higher levels of total protein per ml lavage fluid (0.49 vs. 0.30 mg/ml). A significant increase in the absolute and relative amounts of a low molecular weight glycoprotein (15,000 mol wt) was noted in lavage specimens from CF patients. Reserpine-treated rats also showed a significant increase in the total protein recovered in the lung lavage fluid with a 233% increase in the absolute and relative amounts of a low molecular weight glycoprotein (15,000 mol wt). Thus, reserpine induced changes in the secretions of the lung of the rat which are similar to those observed in samples obtained from the lung of CF patients.

Adult↗
PubMed1975

Pigs susceptible to energy metabolism in the fulminant hyperthermia stress syndrome.

Pigs susceptible to the fulminant hyperthermia-stress syndrome spontaneously developed the hyperthermia syndrome. Basal metabolic rates 10-fold higher than normal were observed in these animals. The metabolic rate exceeded a 17-fold increase over normal with a total heat production of over 28.25 J (6;76 kcal) h-1 kg-1. Heat loss by radiation ceased early in the syndrome, possibly owing to intense peripheral vasoconstriction--a finding which suggests that in man vasodilators might have an important therapeutic role.

Animals↗
PubMed1975

Modification of pig heart lipoamide dehydrogenase by cupric ions.

The insertion of a second disulfide bridge into native pig heart lipoamide dehydrogenase, requires two Cu-2+ ions for each catalytic center inactivated under anaerobic conditions. During inactivation, both metal atoms become reducible by their juxtaposition to the two participating cysteine residues and may be removed as the Cu+-chelates of neocuproine and bathocuproinesulfonate, leaving an additional disulfide bridge on the protein. Inactivation does not require the presence of oxygen, but when substoichiometric levels of copper are used under aerobic conditions the slow regeneration of Cu-2+ becomes rate-limiting. The course of aerobic inactivation is markedly biphasic at 0 degrees using 2 Cu-2+/FAD, with 30% of the total change completed rapidly, followed by a much slower phase. Both the extent of the fast phase and the rate of the second phase are enhanced by increasing levels of Cu-2+, but are relatively unaffected when the Cu-2+/FAD ratio is maintained at 2 and the protein concentration is varied. The enzyme affords several binding sites for Cu-2+ at pH 7.8, and it is suggested that competition between these sites during the initial statistical distribution of metal ions may explain this biphasic behavior.

Anaerobiosis↗
PubMed1975

The sequence of amino acid residues around the oxidation-reduction active disulfide in yeast glutathione reductase.

A 14-residue peptide containing the oxidation-reduction active cystine residue from yeast glutathione reductase has been isolated from proteolytic digests of the enzyme in which the free sulfhydryl groups had been reacted with N-ethylmaleimide. The sequence of this disulfide-containing peptide was found to be:(see article). The sequence was highly homologous with the active cystine regions in Escherichia coli and pig heart lipoamide dehydrogenase. The sequences of three of the postulated four thiol-containing regions of the enzyme are also presented, as well as evidence supporting the view that the enzyme is composed of two identical subunits.

Amino Acid Sequence↗
PubMed1975

Rapid diagnosis of primary influenza pneumonia.

Primary influenza pneumonia is a disease of high mortality. Differentiation between a bacterial and viral etiology for the pulmonary infiltrates frequently presents a diagnostic dilemma. Rapid diagnosis is essential; and once established, the patient requires careful supportive therapy. This report describes two patients with primary influenza pneumonia complicated by severe respiratory failure. Early diagnosis of the pulmonary infiltrates was accomplished by obtaining bronchial secretions with fiberoptic bronchoscopy and staining them with influenza-A fluorescent conjugate. One patient died of the complications of this illness, despite maximal supportive therapy. The other patient survived the illness and at the time of hospital discharge was showing marked improvement in his exercise tolerance. There was subsequent gradual return of ventilation and gas transport function to normal values.

Female↗