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Biomedical subjects

W J Albery

Publications and source records attributed to W J Albery.

16 recordsLinked to original sources
PubMed1991

Molecular recognition and molecular sensors.

Enzyme-substrate recognition provides a convenient and powerful basis on which to construct molecular sensors. In direct enzyme electrodes the rate of the enzyme reaction is transduced into a current using an electrode made of a conducting organic salt. In vivo microelectrodes designed to measure glucose have been constructed and used in the brain of the freely moving rat. Another strategy is to use enzymes that operate with NADH; the NADH can readily be oxidized on conducting organic salt electrodes. Results for the measurement of micellar equilibria involving bile acids are presented. The packed-bed wall-jet electrode provides a device of greater sensitivity; results for the measurement of femtomoles of acetylcholine obtained by microdialysis from cerebral fluid demonstrate the power of this method. The wall-jet ring-disc electrode can be used in an electrochemical immunoassay again at the femtomole level. Finally, enzyme inhibition can be used to make a sensor for toxic substances such as H2S at the p.p.m. level.

Acetylcholine↗
PubMed1979

O2 and N2O analysis with a single intravascular catheter electrode. An in-vitro study.

The simultaneous measurement of O2 and N2O in liquid, using a single polarographic catheter electrode, is described. It is shown that commercial PO2 intravascular electrodes, with silver cathodes, produce separate and distinct polarograms for O2 and N2O, and that these electrodes can be used for the measurement of both PO2 and PN2O.

Blood Gas Analysis↗
PubMed1979

Percutaneous absorption: interfacial transfer kinetics.

A new rotating diffusion cell is described in which a solute diffuses through a rotating filter. The transport of the solute to both sides of the filter is controlled by the rotation. The filter is filled with an organic phase. The rate of transfer of the solute through the filter is determined by the transport and by the kinetics of the interfacial transfer reactions. Since the transport is controlled the rate constant for the transfer reaction can be measured. Results for eleven different systems are reported and it is found that the rate constants are all smaller than 10(-4) ms-1.

Diffusion↗
PubMed1979

Percutaneous absorption: theoretical description.

Equations are derived to describe the percutaneous absorption of a substance through the epidermal barrier. The treatment includes interfacial barriers and allows for the depletion of the substance in the external phase. The equations are derived both for the continuous application and for pulse experiments where the drug is applied for a time, then removed, and the response occurs some time after the removal of the drug. Competition between the drug diffusing through the keratinized cells (transcellular route) and diffusing in the interstitial channels around the cells (intercellular route) is also considered.

Kinetics↗
PubMed1979

Percutaneous absorption: in vivo experiments.

The percutaneous absorption of esters of nicotinic acid has been studied in vivo in man. The time for erythema to be produced has been measured both when the ester is applied continuously and in 'pulse' experiments when the ester is removed before the erythema develops. The results show that the erythema is produced long before steady state diffusion across the epidermis is established and the penetration of methyl nicotinate is characterized by D/l2 = 2.3 X 10(-4)s-1 where D is the diffusion coefficient and l the thickness of the barrier. Results using glycerol water mixtures in the external phase show that the route of penetration for methyl nicotinate is through the interstitial channels and not through the keratinized cells. Data for absorption from various creams and ointments (Barrett et al 1964) show that the route is independent of the nature of the external phase. Steady state data for the absorption of salicylic acid and carbinoxamine through the abdominal skin of guinea-pigs (Arita et al 1970) show that the route of penetration does not change as the experiment proceeds. Data for the absorption of other substances (Michaels et al 1975) also fit the interstitial route.

Diffusion↗
PubMed1978

An electrode for PN2O and PO2 analysis in blood and gas.

The development of a new polarographic sensor for measuring simultaneously both N2O and O2, in either gas or blood, is described. The cathode is made of silver, and it is shown that silver deposition on normal platinum or gold cathode electrodes can result in an enhancement of a PO2 signal, when measured in the presence of nitrous oxide. Silver can be deposited on the cathode by means of Ag+ ions diffusing through the electrolyte from an Ag/AgCl reference electrode. The use of an Ag cathode enables both O2 and N2O signals to be measured.

Blood Gas Analysis↗
PubMed1976

Deuterium and tritium exchange in enzyme kinetics.

The theory of the isotopic exchange of deuterium and tritium between an enzyme-substrate complex and the solvent is derived for 16 different types of experiment involving measurements of initial velocities and of the isotopic content of the reactants and products as a function of the extent of reaction. It is shown how the data from these experiments can be analyzed to obtain the rate constants for the individual steps and thereby the Gibbs free energies of the intermediates and transition states in the reaction. The effects of isotopic substitution on each intermidiate and transition state are also found and this allows conclusions to be drawn as to the extent to which a proton is in flight in a particular transition state. Neither substrate handling (that is, on-off steps), nor the isotopic exchange with the solvent, is assumed to be rapid.

Deuterium↗
PubMed1976

Energetics of triosephosphate isomerase: the appearance of solvent tritium in substrate dihydroxyacetone phosphate and in product.

When the isomerization of dihydroxyacetone phosphate to D-glyceraldehyde 3-phosphate is catalyzed by triosephosphate isomerase in tritiated water, both the substrate and product become labeled. The specific radioactivity of the product is about 80% that of the solvent, which shows that the protonation of the enediol intermediate at C-2 (to form the enzyme-bound product D-glceraldehyde 3-phosphate) is followed by a slower step not involving proton transfer. The specific radioactivity of the remaining substrate after partial reaction rises as the reaction proceeds and shows that the reaction intermediate that exchanges protons with the medium returns to dihydroxyacetone phosphate (picking up tritium) about one-third as often as it is converted to D-glceraldehyde 3-phosphate. These results allow a qualitative description of the relative heights of the energy barriers in the catalyzed reaction and contribute to the quantitative analysis of the energetics of the process.

Carbohydrate Epimerases↗
PubMed1976

Energetics of triosephosphate isomerase: the appearance of solvent tritium in substrate glyceraldehyde 3-phosphate and in product.

When the isomerization of D-glyceraldehyde 3-phosphate to dihydroxyacetone phosphate is catalyzed by triosephosphate isomerase in tritiated water, both the substrate and the product become labeled. The specific radioactivity of the product is only about 13% that of the solvent, which shows that the protonation of the enediol intermediate at C-1 (to form the enzyme-bound product dihydroxyacetone phosphate) is a kinetically significant step, and that the rate of loss of dihydroxyacetone phosphate from the enzyme is relatively fast. The specific radioactivity of the remaining substrate after partial reaction rises as the reaction proceeds and shows that the reaction intermediate that exchanges protons with the medium returns to D-glyceraldehyde 3-phosphate about one-third as often as it is converted to dihydroxyacetone phosphate. These results confirm the qualitative description of the relative heights of the energy barriers in this reaction and further contribute to the quantitative analysis of the free-energy profile.

Carbohydrate Epimerases↗
PubMed1976

Energetics of triosephosphate isomerase: deuterium isotope effects in the enzyme-catalyzed reaction.

The effect of isotopic substitution of the specifically labilized hydrogen in the substrates of triosephosphate isomerase on the steady-state rates of the enzyme-catalyzed reaction has been examined. The k cat value for the enzyme-catalyzed transformation of [1(R)-2H] dihydroxyacetone phosphate is 2.9 times smaller than that for the 1(R)-1H compound. Because of the rapid loss of 2H to solvent from the enzyme-enediol complex, this factor represents the full kinetic isotope effect of the proton abstraction step. The values of k cat and of Km for D-[2-2H]glyceraldehyde 3-phosphate are indistinguishable from those of the 2-1H material. This arises from the rapid loss of 2H from the enzyme-enediol intermediate, which results in 1H rather than 2H transfer in the rate-limiting step. The steady-state kinetic results reported in this paper qualitatively confirm and quantitatively extend the results from the previous papers on the variation of the free energy along the reaction path.

Carbohydrate Epimerases↗
PubMed1976

Energetics of triosephosphate isomerase: the nature of the proton transfer between the catalytic base and solvent water.

The isomerization of specifically deuterium-labeled [1(R)-2H5dihydroxyacetone phosphate to D-glyceraldehyde 3-phosphate, catalyzed by the enzyme triosephosphate isomerase, has been studied. It is shown that the extent of transfer of the 2H label from the substrate to the product D-glyceraldehyde 3-phosphate is (after complete reaction) the same as that of the corresponding transfer of 3H. The absence of an isotope effect shows that the exchange process of the tstopically labeled enzyme carboxyl group, -COOL H2O leads to -COOH + LOH, does not tnvolve a rate-limiting transition state in which L is the flight. Possible modes for the nature of the ionization of -COOL in 1H2O are discussed.

Carbohydrate Epimerases↗
PubMed1976

Free-energy profile of the reaction catalyzed by triosephosphate isomerase.

The experimental results on the interconversion of dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate catalyzed by triosephosphate isomerase that are presented in the previous five papers are here collected and analyzed according to the theory presented in the first paper (Albery, W.J., Knowles, J.R. (1976), Biochemistry 15, the first of eight papers in a series in this issue). The rate constants and fractionation factors so derived allow the construction of theGibbs free-energy profile for this enzyme-catalyzed reaction.

Carbohydrate Epimerases↗
PubMed1975

Electrochemical improvement of the performance of PO2 electrodes.

Rotating ring-disc electrode studies have indicated that relatively large quantities of hydrogen peroxide ion, HO2-, are produced when oxygen is reduced at a platinum or gold polarographic electrode surface. The electrochemical reduction processes are improved and the quantity of HO2- is reduced by using alkaline buffer electrolytes (pH 10 to 11) and by polarising the electrode at voltages more negative than -0.9 V. The presence of HO2- in the electrolyte has been shown to be the cause of excessively long time response in both blood-gas and respiratory polarographic PO2 electrodes; electrode alinearity on micro-blood-gas PO2 electrodes has also been shown to be due to the absence of a plateau on the polarogram of electrodes when used with conventional electrolytes. The use of a high pH buffer and high negative voltage results in a long, flat plateau and a marked improvement in both electrode linearity and response time. This two-fold improvement in electrode performance holds true for both platinum and gold polarographic respiratory gas and blood-gas PO2 electrodes.

Blood Gas Analysis↗