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Biomedical subjects

J Colby

Publications and source records attributed to J Colby.

At least 37 records · Page 2Linked to original sources
PubMed1983

Implications of normal exercise electrocardiographic results in patients with angiographically documented coronary artery disease. Correlation with left ventricular function and myocardial perfusion.

The purpose of this study was to examine the incidence and implications of false-negative exercise electrocardiographic results among 216 consecutive patients with angiographically documented coronary artery disease (50 percent diameter narrowing or greater of one or more vessels). Exercise electrocardiography gave negative (false-negative) results in 23 patients and positive (true-positive) results in 102 patients, and were nondiagnostic in the rest. Exercise thallium-201 imaging was performed in 88 patients. The extent of coronary artery disease was quantitated by a scoring system that takes into consideration the degree and site of narrowing in the major vessels and their branches. The exercise heart rate was higher in patients with false-negative than in patients with true-positive exercise electrocardiographic results (161 +/- 18 versus 133 +/- 24 beats per minute, mean +/- SD; p less than 0.0001). Q-wave infarction was present in two patients (9 percent) with false-negative and 20 patients (20 percent) with true-positive exercise electrocardiographic results (p = NS); left ventricular asynergy at rest was observed in 13 patients (57 percent) with false-negative and in 74 patients (74 percent) with true-positive results (p = NS). Patients with false-negative results had less extensive coronary disease than did patients with true-positive results (score 5.8 +/- 3.6 versus 9.2 +/- 5.0; p = 0.0025). Angina during exercise was less frequent in patients with false-negative results (p less than 0.01). Abnormal exercise thallium-201 images were seen in 15 of 20 patients (75 percent) with false-negative results and in 56 of 68 patients (82 percent) with true-positive results (p = NS). It is concluded that (1) false-negative exercise electrocardiographic results are infrequent (10 percent) among patients with coronary artery disease and are associated with less extensive coronary artery disease; (2) the frequency of Q-wave infarction and left ventricular asynergy is the same in patients with false-negative results as in patients with true-positive exercise electrocardiographic results; (3) exercise thallium images can identify 75 percent of patients with coronary disease and false-negative results of exercise electrocardiography.

Adult↗
PubMed1983

Poor R wave progression in the precordial leads: clinical implications for the diagnosis of myocardial infarction.

A definite diagnosis of anterior myocardial infarction is often difficult to make in patients when a pattern of poor R wave progression in the precordial leads is present on the electrocardiogram. The purpose of this study was to determine whether a mathematical model could be devised to identify patients with anterior infarction among 102 consecutive patients with poor R wave progression. Each patient underwent exercise testing with thallium scanning. The diagnosis of anterior infarction was established in 20 (20%) of the 102 patients by the presence of fixed thallium-201 perfusion defects in the anterior wall or septum, or both. With the use of a multivariate stepwise discriminant analysis of clinical and electrocardiographic variables, five variables (sex, ST-T changes, S wave amplitude in leads V2 and V3 and the sum of the R wave amplitude in leads V3 and V4) that were statistically significant by univariate analysis were selected by the model to identify patients with anterior infarction (sensitivity 85%, specificity 71%). The discriminant model was subsequently applied prospectively to an additional 21 patients with poor R wave progression and provided a sensitivity of 85% and a specificity of 88%. Thus, anterior infarction (fixed thallium-201 defects in the anteroseptal segments) was present in 20% of patients with poor R wave progression in the precordial leads; and a mathematical model can be used to identify a subset of patients with anterior infarction in a group of patients with poor R wave progression.

Adult↗
PubMed1983

Hemodynamic, angiographic and scintigraphic correlates of positive exercise electrocardiograms: emphasis on strongly positive exercise electrocardiograms.

The results of treadmill exercise electrocardiograms were analyzed in 179 patients with coronary artery disease (greater than or equal to 50% diameter narrowing of one or more vessels). Exercise thallium-201 images were available in 141 of these patients. The exercise electrocardiograms were strongly positive in 51 patients, mildly positive (1 to 1.9 mm ST depression) in 28 patients, falsely negative in 23 patients and uninterpretable in 77 patients. The degree of exercise-induced ST depression did not correlate with left ventricular function, extent of coronary artery disease, exercise heart rates and rate-pressure product and extent of exercise-induced thallium-201 perfusion abnormality. However, the presence of a strongly positive exercise electrocardiogram only at heart rates of 140 beats/min or more or stage III or higher of the Bruce protocol was predictive of less extensive coronary disease and perfusion abnormalities. Thus, the magnitude of ST depression as such during exercise is not predictive of the extent of coronary disease, even in patients with 3 mm or greater ST depression. However, a strongly positive exercise electrocardiogram in the first two stages of the Bruce protocol or at a heart rate of less than 140 beats/min was related to the extent of coronary artery disease and impaired myocardial perfusion, and identified patients with more extensive coronary artery disease and jeopardized myocardium. Therefore, caution should be used in interpreting prognostic data on the basis of the degree of exercise-induced ST depression alone.

Adult↗
PubMed1982

Direct evidence against a role of ATP as the nonadrenergic, noncholinergic inhibitory neurotransmitter in guinea pig tenia coli.

Electrical field stimulation of the isolated guinea pig tenia coli in the presence of a muscarinic receptor antagonist (atropine) and an adrenergic neuron blocker (guanethidine) produces relaxation. A large amount of indirect evidence has suggested that the neurotransmitter that is released from these nonadrenergic, noncholinergic inhibitory neurons is ATP or a related nucleotide, and the nerves have been termed "purinergic." A photoaffinity analog of ATP, arylazido aminopropionyl ATP, which produces a specific pharmacological antagonism of P2 purinergic receptors in isolated guinea pig vas deferens and urinary bladder, was utilized in the present study to evaluate directly whether ATP is the nonadrenergic, noncholinergic inhibitory neurotransmitter in tenia coli. By blocking postjunctional P2 receptors, arylazido aminopropionyl ATP produced a pronounced antagonism of relaxations induced by exogenously added ATP. Responses produced by ADP, AMP, and adenosine also were antagonized by arylazido aminopropionyl ATP, but to a lesser extent. Inhibitory responses to isoproterenol were not antagonized. Under these conditions of established, specific P2-receptor blockade of responses to exogenously added ATP, relaxations induced by field stimulation of intrinsic inhibitory nerves in the presence of atropine (1 microM) and guanethidine (1 microM) were not antagonized. Though these results provide no indication of the actual substance involved, they suggest strongly that the nonadrenergic, noncholinergic inhibitory neurotransmitter in the guinea pig tenia coli is not ATP.

Adenosine↗
PubMed1981

Contribution by purines to the neurogenic response of the vas deferens of the guinea pig.

The specific purine-receptor antagonist, arylazido aminopropionyl ATP (ANAPP3), was used to determine if purines released from nerves of the guinea-pig was deferens contribute to the neurogenic response. ANAPP3, which is a photoaffinity label, antagonized contractile responses of the in vitro vas deferens to transmural stimulation, reversibly in the presence of the compound and irreversibly after its photoactivation in the presence of the tissues. The antagonism by ANAPP3 was augmented by depletion of norepinephrine produced by reserpine pretreatment. Responses of untreated tissues were only slightly antagonized by the alpha-adrenoceptor blocker prazosin. However, neurogenic responses were markedly reduced in the combined presence of ANAPP3 and prazosin. ANAPP3 did not affect the release of tritium from tissues prelabeled with [3H]norepinephrine. The initial phasic component of the neurogenic response was preferentially antagonized by ANAPP3 whereas the secondary more tonic component of the response was preferentially antagonized by prazosin and reserpine pretreatment. Small, residual responses remaining after chemical sympathectomy produced by 6-hydroxydopamine pretreatment were potentiated, rather than inhibited, by ANAPP3 and were, unlike untreated tissues, sensitive to atropine. These and previous findings indicate that ATP or a related purine, originating from adrenergic neurons, acts as a co-transmitter with norepinephrine in this tissue.

Adenosine Triphosphate↗
PubMed1979

Characterization of the second prosthetic group of the flavoenzyme NADH-acceptor reductase (component C) of the methane mono-oxygenase from Methylococcus capsulatus (Bath).

1. A new two-step purification is described that routinely yields 100mg quantities of component C for biochemical studies. 2. Chemical analyses show component C purified by this procedure to contain 2 g-atoms of iron, 2 mol of acid-labile sulphide (S) and 1 mol of FAD per mol of protein. 3. The Fe-S core of component C was extruded by treating the protein with p-methoxybenzenethiol in hexamethyl phosphoramide/50mM-Tris/HCl buffer, pH 8.5 (4:1, v/v), under anaerobic conditions. The spectral properties of the extruded core suggest that component C contains 1 mol of [2Fe-2S(S-Cys)4] centre per mol of protein. 4. E.p.r. spectroscopy confirms the presence of a Fe-S centre in component C. 5. Component C catalyses the reduction by NADH of ferricyanide, 2,6-dichlorophenol-indophenol or horse heart cytochrome c, with specific activities of 50--230 units/mg of protein. 6. The optimum pH for the NADH-acceptor reductase activity is 8.5--9.0, and the apparent Km values for NADH and NADPH are 0.05mM and 15.5mM respectively. 7. Unlike methane mono-oxygenase activity, NADH-acceptor reductase activity of component C is not inhibited by 8-hydroxyquinoline or by acetylene.

Electron Spin Resonance Spectroscopy↗
PubMed1979

A comparison of the substrate and electron-donor specificities of the methane mono-oxygenases from three strains of methane-oxidizing bacteria.

1. Methane mono-oxygenase from Methylosinus trichosporium has the same broad substrate specificity as the analogous enzyme from Methylococcus capsulatus (Bath); the enzyme from Methylomonas methanica is more specific. 2. Contrary to previous reports, NAD(P)H and not ascorbate is the required electron donor for the enzyme from Methylosinus trichosporium. 3. It is concluded that these three bacteria contain similar methane mono-oxygenases.

Methane↗
PubMed1978

Resolution of the methane mono-oxygenase of Methylococcus capsulatus (Bath) into three components. Purification and properties of component C, a flavoprotein.

1. Ion-exchange chromatography resolves the methane mono-oxygenase from soluble extracts of Methylococcus capsulatus (Bath) into three fractions. 2. Fractions A and B are comparatively stable at 0 degrees C, whereas fraction C is very unstable unless kept in the presence of sodium thioglycollate (1-10 mM) or dithiothreitol (5-10mM). 3. The active component from fraction C was purified some 80-fold. 4. Purified component C has mol. wt. 42000. Its solutions are yellow with absorption maxima at 270 and 465 nm and a shoulder at 395 nm. The 465 nm peak is abolished by reduction with NADH or sodium dithionite, or by photoreduction in the presence of EDTA. A new spectral species, probably a neutral flavin semiquinone, is observed on partial reduction of component C. 5. No copper was detected in samples of purified component C, but the protein contains 1.3-1.5 atoms of iron/molecule. 6. On boiling, component C releases a yellow-green fluorescent material that has been identified as FAD from its absorption and fluorescence spectra and by t.l.c. 7. Component C contains 1 mol of FAD/mol of protein.

Copper↗
PubMed1977

The soluble methane mono-oxygenase of Methylococcus capsulatus (Bath). Its ability to oxygenate n-alkanes, n-alkenes, ethers, and alicyclic, aromatic and heterocyclic compounds.

1. Methane mono-oxygenase of Methylococcus capsulatus (Bath) catalyses the oxidation of various substituted methane derivatives including methanol. 2. It is a very non-specific oxygenase and, in some of its catalytic properties, apparently resembles the analogous enzyme from Methylomonas methanica but differs from those found in Methylosinus trichosporium and Methylomonas albus. 3. CO is oxidized to CO2. 4. C1-C8 n-alkanes are hydroxylated, yielding mixtures of the corresponding 1- and 2-alcohols; no 3- or 4-alcohols are formed. 5. Terminal alkenes yield the corresponding 1,2-epoxides. cis- or trans-but-2-ene are each oxidized to a mixture of 2,3-epoxybutane and but-2-en-1-ol with retention of the cis or trans configuration in both products; 2-butanone is also formed from cis-but-2-ene only. 6. Dimethyl ether is oxidized. Diethyl ether undergoes sub-terminal oxidation, yielding ethanol and ethanal in equimolar amounts. 7. Methane mono-oxygenase also hydroxylates cyclic alkanes and aromatic compounds. However, styrene yields only styrene epoxide and pyridine yields only pyridine N-oxide. 8. Of those compounds tested, only NADPH can replace NADH as electron donor.

Alkanes↗
PubMed1976

Some properties of a soluble methane mono-oxygenase from Methylococcus capsulatus strain Bath.

Soluble extracts of Methylococcus capsulatus (Bath), obtained by centrifugation of crude extracts at 160000g for 1h, catalyse the NAD(P)H- and O2-dependent disappearance of bromomethane, and also the formation of methanol from methane. Soluble methane mono-oxygenase is not inhibited by chelating agents or by most electron-transport inhibitors, and is a multicomponent enzyme.

Electron Transport↗
PubMed1975

Tricarboxylic acid-cycle and related enzymes in restricted facultative methylotrophs.

The isolation is described of pure cultures of three non-methane-utilizing methylotrophic bacteria which, together with the previously described Bacillus PM6, have a very limited range of growth substrates; these organisms are designated "restricted facultative' methylotrophs. Two of these isolates, W6A and W3A1, grow only on glucose out of 50 non-C1 compounds tested, whereas the third isolate S2A1 and Bacillus PM6 grow on betaine, glucose, gluconate, alanine, glutamate, citrate and nutrient agar, but not on any of a further 56 non-C1 compounds. Crude sonic extracts of trimethylamine-grown and glucose-grown W6A and W3A1 isolates, and of trimethylamine-grown C2A1 (an obligate methylotroph) contain (i) no detectable 2-oxogltarate dehydrogenase activity, (ii) very low or zero specific activities of succinate dehydrogenase and succinyl-CoA synthetase and (iii) NAD+-dependent isocitrate dehydrogenase activity. Extracts of trimethylamine-grown PM6 and S2A1 methylotrophs have (i) very low 2-oxoglutarate dehydrogenase specific activities, (ii) comparatively high specific activities of succinate dehydrogenase, malate dehydrogenase and succinyl-CoA synthetase and (iii) NADP+-dependent isocitrate dehydrogenase activity but no NAD+-dependent isocitrate dehydrogenase activity. The activities of most of these enzymes are increased during growth on glucose, alanine, glutamate or citrate, but only very low 2-oxoglutarate dehydrogenase activities are present under all growth conditions. The restricted facultative methylotrophs grow on certain non-C1 compounds in the absence of 2-oxoglutarate dehydrogenase and, in some cases, of other enzymes of the tricarboxylic acid cycle; these lesions cannot therefore be the sole cause of obligate methylotrophy.

Bacteria↗
PubMed1975

Enzymological aspects of the pathways for trimethylamine oxidation and C1 assimilation of obligate methylotrophs and restricted facultative methylotrophs.

Extracts of trimethylamine-grown W6A and W3A1 (type M restricted facultative methylotrophs) contain trimethylamine dehydrogenase whereas similar extracts of Bacillus PM6 and Bacillus S2A1 (type L restricted facultative methylotrophs) contain trimethylamine mono-oxygenase and trimethylamine N-oxide demethylase but no trimethylamine dehydrogenase. Extracts of the restricted facultatives and of the obligate methylotroph C2A1 contain hexulose phosphate synthase-hexulose phosphate isomerase activity; hydroxypyruvate reductase was not detected. Neither the restricted facultatives nor the obligates 4B6 and C2A1 contain all the enzymes of the hexulose phosphate cycle of formaldehyde assimilation as originally proposed by Kemp & Quayle (1967). Organisms PM6 and S2A1 lack transaldolase and use a modified cycle involving sedoheptulose 1,7-diphosphate and sedoheptulose diphosphatase. The obligates 4B6 and C2A1, and the type M organisms W6A and W3A1, use a different modification of the assimilatory hexulose phosphate cycle involving the Entner-Doudoroff-pathway enzymes phosphogluconate dehydratase and phospho-2-keto-3-deoxygluconate aldolase. The lack of fructose diphosphate aldolase and hexose diphosphatase in these organisms may be a partial explanation of their restricted growth-substrate range. Enzymological evidence suggests that all the obligates and the restricted facultatives use a dissimilatory hexulose phosphate cycle to accomplish the complete oxidation of formaldehyde to CO2 and water.

Aldehyde-Lyases↗
PubMed1975

Regulation of citrate synthase activity in methylotrophs by reduced nicotinamide-adenine dinucleotide, adenine nucleotides and 2-oxoglutarate.

Citrate synthase from two typical facultative methylotrophs, but not from four obligate methylotrophs or from two restricted facultative methylotrophs, is inhibited by 0.1 mM-NADH. ATP or ADP (both at 10mM) inhibits all the citrate synthases, whereas 2-oxoglutarate (10mM) inhibits those from only three of the eight methylotrophs.

Adenine Nucleotides↗
PubMed1975

An improved assay for bacterial methane mono-oxygenase: some properties of the enzyme from Methylomonas methanica.

Extracts of Methylomonas methanica catalyse the O2-and NAD(P)H-dependent disappearance of bromomethane. The activity is unstable at 2 degrees C but is stable at --70 degrees C for several weeks. Bromomethane mono-oxygenase is particulate and is inhibited by metal-binding reagents, by compounds SKF 525A and Lilly 53325, by some metal ions and by acetylene. Evidence is presented that indicates that bromomethane mono-oxygenase is the enzyme responsible for methane oxidation in vivo.

Hydrogen-Ion Concentration↗
PubMed1975

Assimilation of exogenous fructose, aspartate and some organic acids during the growth of methylotrophs.

The percentage of bacterial carbon that was derived from exogenous labelled compounds present in the medium during the growth of some methylotrophs on trimethylamine or on non-C1 compounds was determined. Less than 10% of bacterial carbon was derived from acetate during the growth of the obligate methylotrophs 4B6 and C2A1, and of the restricted facultative methylotroph PM6; the other restricted facultative methylotroph W3A1 gave a value of 18%. Corresponding values for three typical facultative methylotrophs growing on trimethylamine were 41, 42 and 52%. Aspartate, fructose, pyruvate and succinate made only a small percentage contribution (0-4 to 12%) to bacterial carbon in 4B6, C2A1, W3A1 and PM6. Washed suspensions of 4B6, C2A1, W3A1 and PM6, all grown on trimethylamine, assimilated labelled acetate only in the presence of trimethylamine and there was a linear relationship between the amount of acetate assimilated and the amount of trimethylamine oxidized. Organisms 4B6, C2A1, W3A1 and PM6 assimilated 14C from labelled acetate predominantly into lipid (except PM6), glutamate, arginine, proline and leucine, whereas the typical facultative methylotrophs assimilated 14C from acetate into lipid, nucleic acid and all the protein amino acids. These results are consistent with the presence of a deficient tricarboxylic acid cycle in the obligate methylotrophs and in the restricted facultative methylotrophs.

Acetates↗
PubMed1974

Purification and properties of the trimethylamine dehydrogenase of bacterium 4B6.

1. The trimethylamine dehydrogenase of bacterium 4B6 was purified to homogeneity as judged by analytical polyacrylamide-gel electrophoresis. The specific activity of the purified enzyme is 30-fold higher than that of crude sonic extracts. 2. The molecular weight of the enzyme is 161000. 3. The kinetic properties of the purified enzyme were studied by using an anaerobic spectrophotometric assay method allowing the determination of trimethylamine dehydrogenase activity at pH8.5, the optimum pH. The apparent K(m) for trimethylamine is 2.0+/-0.3mum and the apparent K(m) for the primary hydrogen acceptor, phenazine methosulphate, is 1.25mm. 4. Of 13 hydrogen acceptors tested, only Brilliant Cresyl Blue and Methylene Blue replace phenazine methosulphate. 5. A number of secondary and tertiary amines with N-methyl and/or N-ethyl groups are oxidized by the purified enzyme; primary amines and quaternary ammonium salts are not oxidized. Of the compounds that are oxidized by the purified enzyme, only trimethylamine and ethyldimethylamine support the growth of bacterium 4B6. 6. Trimethylamine dehydrogenase catalyses the anaerobic oxidative N-demethylation of trimethylamine with the formation of stoicheiometric amounts of dimethylamine and formaldehyde. Ethyldimethylamine is also oxidatively N-demethylated yielding ethylmethylamine and formaldehyde; diethylamine is oxidatively N-de-ethylated. 7. The activity of the purified enzyme is unaffected by chelating agents and carbonyl reagents, but is inhibited by some thiol-binding reagents and by Cu(2+), Co(2+), Ni(2+), Ag(+) and Hg(2+). Trimethylamine dehydrogenase activity is potently inhibited by trimethylsulphonium chloride, by tetramethylammonium chloride and other quaternary ammonium salts, and by monoamine oxidase inhibitors of the substituted hydrazine and the non-hydrazine types. 8. Inhibition by the substituted hydrazines is time-dependent, is prevented by the presence of trimethylamine or trimethylamine analogues and in some cases requires the presence of the hydrogen acceptor phenazine methosulphate. The inhibition was irreversible with the four substituted hydrazines that were tested.

Anaerobiosis↗