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Biomedical subjects

G Lowe

Publications and source records attributed to G Lowe.

At least 109 records · Page 6Linked to original sources
PubMed1988

Beta-lactamase inhibitors. The inhibition of serine beta-lactamases by specific boronic acids.

Many beta-lactamases have active-site serine residues, and are competitively inhibited by boronic acids. Hitherto, the boronic acids used have lacked any structural resemblance to the substrates of beta-lactamases. Phenylacetamidomethaneboronic acid, trifluoroacetamidomethaneboronic acid and 2,6-dimethoxybenzamidomethaneboronic acid have now been synthesized. The first of these contains the side-chain moiety of penicillin G, and the last that of methicillin. The pH-dependence of binding of the first inhibitor to beta-lactamase I from Bacillus cereus revealed pK values of 4.7 and 8.2 for (presumably) active-site groups in the enzyme. The kinetics of inhibition were studied by cryoenzymology and by stopped-flow spectrophotometry. These techniques provided evidence for a two-step mechanism of binding of the first two boronic acids mentioned above to beta-lactamase I, and for benzeneboronic acid to a beta-lactamase from Pseudomonas aeruginosa. The slower step is probably associated with a change in enzyme conformation as well as the formation of an O-B bond between the active-site serine hydroxy group and the boronic acid.

Bacillus cereus↗
PubMed1988

A new synthesis of adenosine 5'-([gamma(R)-17O,18O]-gamma-thiotriphosphate) and its use to determine the stereochemical course of the activation of glutamate by glutamine synthetase.

A new synthetic route to adenosine 5'-([gamma(R)-17O,18O]-gamma-thiotriphosphate) is described which combines chemical methods for introducing the heavy oxygen isotopes and enzymic methods for achieving the enantiospecificity. This material was used as a substrate for the activation of glutamate catalyzed by glutamine synthetase from Salmonella typhimurium. Analysis of the chirality of the [16O,17O,18O]thiophosphate produced showed that the reaction proceeds with inversion of configuration on phosphorus. This result, taken together with the positional isotope exchange studies of Midelfort and Rose [Midelfort, C. F., & Rose, I.A. (1976) J. Biol. Chem. 251, 5881-5887], demonstrates that the activation of glutamate to form gamma-glutamyl phosphate proceeds by a direct "in-line" transfer of the phosphoryl group.

Adenosine Triphosphate↗
PubMed1987

The proton flux through the bacterial flagellar motor.

Bacterial flagella are driven by a rotary motor that utilizes the free energy stored in the electrochemical proton gradient across the cytoplasmic membrane to do mechanical work. The flux of protons coupled to motor rotation was measured in Streptococcus and found to be directly proportional to motor speed. This supports the hypothesis that the movement of protons through the motor is tightly coupled to the rotation of its flagellar filament. Under this assumption the efficiency of energy conversion is close to unity at the low speeds encountered in tethered cells but only a few percent at the high speeds encountered in swimming cells. This difference appears to be due to dissipation by processes internal to the motor. The efficiency at high speeds exhibits a steep temperature dependence and a sizable deuterium solvent isotope effect.

Flagella↗
PubMed1986

Comparison of methods of plasma volume determination for dose calculation of factor VIII in patients with classic haemophilia.

Plasma volumes have been measured in 12 patients with moderate or severe haemophilia A and compared with plasma volumes derived by calculation using a variety of commonly recommended formulae based on body weight with or without a correction for haematocrit. The mean plasma volume by measurement was 47 ml/kg. A calculated plasma volume using 42 ml/kg and a correction for haematocrit most closely approximated the measured results. The correlation coefficient was 0.9. Ex vivo factor VIII recoveries, following infusion of either lyophilised cryoprecipitate or NZFVIII (controlled pore glass preparation), were then determined based on the observed/expected response assuming different values for plasma volume. Mean recoveries of approximately 100% were associated with a 2.4% FVIII rise per unit/kg administered using cryoprecipitate. Ex vivo recoveries following NZFVIII exceeded 100% with mean values, depending on the technique used for plasma volume determination, up to 131%. Recoveries were not significantly affected by the plasma volume method used and all methods indicated that the labelled potency of NZFVIII is currently being underestimated by at least 20-30%.

Body Height↗
PubMed1986

The stereochemical course of phosphoryl transfer catalyzed by herpes simplex virus type I-induced thymidine kinase.

Herpes simplex virus type I (HSV-I)-induced thymidine kinase has been shown to catalyze phosphoryl transfer from adenosine 5'-[gamma-(S)-16O,17O,18O]triphosphate to thymidine with inversion of configuration at phosphorus. The simplest interpretation of this result is that phosphoryl transfer occurs by a single in-line group transfer between ATP and thymidine within the ternary enzyme complex.

Adenosine Triphosphate↗
PubMed1986

State-dependent learning effects with a combination of alcohol and nicotine.

An experiment was carried out to investigate whether nicotine ingestion (via cigarette smoking) interacted with alcohol (vodka and tonic) in its effect on state-dependent learning (SDL) in humans. On Day 1 of the 2-day experiment 24 subjects were required to learn a simple route map previously found to be SDL sensitive with alcohol. All subjects ingested 0.66 g alcohol/kg body wt. and smoked two medium tar cigarettes (average nicotine content 1.4 mg). Twenty-four hours later, subjects attempted recall under one of the following drug states; (i) alcohol and nicotine (A + N); (ii) alcohol and smoking placebo (A + O); (iii) Nicotine and placebo drink (O + N); and (iv) no drugs (O + O). Highest recall scores were observed in the A + N subjects, with O + N and O + O subjects recalling the least. A + O subjects had intermediate recall performance. Thus the combination did produce a clear SDL effect, with alcohol possibly contributing the major influence.

Adolescent↗
PubMed1985

A stereochemical study of the mechanism of activation of donor oligonucleotides by RNA ligase from bacteriophage T4 infected Escherichia coli.

RNA ligase from bacteriophage T4 infected Escherichia coli catalyzes the activation of adenosine 3',5'-bisphosphate (representing the donor oligonucleotide) by adenosine 5'-[(S)-alpha-17O,alpha,alpha-18O2]triphosphate with retention of configuration at P alpha. Since single-step enzyme-catalyzed nucleotidyl transfer reactions proceed with inversion, this stereochemical result provides support for a double displacement mechanism involving an adenylyl-enzyme intermediate as proposed previously from isotope exchange experiments.

Adenine Nucleotides↗
PubMed1985

Mechanism of activation of phenylalanine and synthesis of P1, P4-bis(5'-adenosyl) tetraphosphate by yeast phenylalanyl-tRNA synthetase.

The activation of L-phenylalanine by yeast phenylalanyl-tRNA synthetase using adenosine 5'-[(S)-alpha-17O,alpha,alpha-18O2]triphosphate is shown to proceed with inversion of configuration at P alpha of ATP. This observation taken together with the lack of positional isotope exchange when adenosine 5'-[beta,beta-18O2]triphosphate is incubated with the enzyme in the absence of phenylalanine and in the presence of the competitive inhibitor phenylalaninol indicates that activation of phenylalanine occurs by a direct "in-line" adenylyl-transfer reaction. In the presence of Zn2+, yeast phenylalanyl-tRNA synthetase also catalyzes the phenylalanine-dependent hydrolysis of ATP to AMP and the synthesis of P1,P4-bis(5'-adenosyl) tetraphosphate (Ap4A). With adenosine 5'-[(S)-alpha-17O,alpha,alpha-18O2]triphosphate, the formation of AMP and Ap4A is shown to occur with inversion and retention of configuration, respectively. It is concluded that phenylalanyl adenylate is an intermediate in both processes, Zn2+ promoting AMP formation by hydrolytic cleavage of the C-O bond and Ap4A formation by displacement at phosphorus of phenylalanine by ATP.

Adenine Nucleotides↗
PubMed1984

An investigation of the mechanism of activation of tryptophan by tryptophanyl-tRNA synthetase from beef pancreas.

Adenosine (S)-5'-[alpha-17O, 18O2]triphosphate has been synthesized and used to investigate the stereochemical course of activation of tryptophan by tryptophanyl-tRNA synthetase from beef pancreas. It is shown that the reaction proceeds by displacement of Mg pyrophosphate from MgATP with inversion of configuration at P alpha. Tryptophanyl-tRNA synthetase catalyses positional isotope exchange in adenosine 5'-[beta-18O2]triphosphate in the presence of tryptophan but not in its absence or in the presence of the competitive inhibitors tryptamine and tryptophanol. These observations eliminate a multi-adenylyl transfer or dissociative mechanism and in combination with the sterochemical study leave a direct associative 'in line' displacement at P alpha of MgATP as the only tenable mechanism for the activation of tryptophan by tryptophanyl-tRNA synthetase.

Adenosine Triphosphate↗
PubMed1983

The stereochemical course of nucleotidyl transfer catalysed by NAD pyrophosphorylase.

NAD pyrophosphorylase catalyses nucleotidyl transfer from adenosine (R)-5'-[alpha-17O]triphosphate to nicotinamide mononucleotide with inversion of configuration at the alpha-P giving (S)-[17O]NAD+. The simplest interpretation of this observation is that the adenylyl group is transferred directly from ATP to the co-substrate by an 'in line' mechanism. It is also shown that snake venom phosphodiesterase hydrolyses NAD+ regio-specifically at the adenylyl terminus of the pyrophosphate bond.

Adenosine Triphosphate↗
PubMed1983

A stereochemical and positional isotope exchange study of the mechanism of activation of isoleucine by isoleucyl-tRNA synthetase from Escherichia coli.

Isoleucyl-tRNA synthetase from Escherichia coli catalyzes the activation of [18O2]isoleucine by adenosine 5'-[(R)-alpha-17O]triphosphate with inversion of configuration at phosphorus. Moreover, isoleucyl-tRNA synthetase does not catalyze positional isotope exchange in adenosine 5'-[beta-18O2]triphosphate in the absence of isoleucine or in the presence of the competitive inhibitor isoleucinol, which effectively eliminates the possibility of either adenylyl-enzyme or adenosine metaphosphate intermediates being involved. Together, these observations require that isoleucyl-tRNA synthetase catalyzes the activation of isoleucine by associative "in line" nucleotidyl transfer. The synthesis of adenosine 5'-[(R)-alpha-17O]diphosphate and its conversion to adenosine 5'-[(R)-alpha-17O]triphosphate is described and an explanation provided for the reported differences between the treatment of adenosine 5'-[(S)-alpha-thiodiphosphate] with cyanogen bromide and bromine in [18O]water.

Amino Acyl-tRNA Synthetases↗
PubMed1983

A stereochemical and positional isotope-exchange study of the mechanism of activation of methionine by methionyl-tRNA synthetase from Escherichia coli.

Methionyl-tRNA synthetase from Escherichia coli catalyses the activation of [18O2]methionine by adenosine 5'-[(R)-alpha 17O]triphosphate with inversion of configuration at P alpha. Furthermore methionyl-tRNA synthetase does not catalyse positional isotope exchange in adenosine 5'-[beta-18O2]triphosphate in the absence of methionine or in the presence of the competitive inhibitor, methioninol, which eliminates the possibility of either adenylyl-enzyme or adenosine metaphosphate intermediates being involved. These observations require that methionyl-tRNA synthetase catalyses the activation of methionine by an associative 'in-line' nucleotidyl transfer mechanism. A kinetic study of positional isotope exchange in adenosine 5'-[beta-18O2]triphosphate in the presence of methionine, Mg2+ and methionyl-tRNA synthetase showed that torsional equilibration (18O exchange into the P alpha--O--P beta bridge) occurs faster than tumbling (18O exchange into P gamma by rotation about the C2 axis of Mg[18O2]PPi), demonstratings that the positional isotope exchange occurs at least in part in the E X Met-AMP X Mg[18O2]PPi complex.

Amino Acyl-tRNA Synthetases↗
PubMed1983

Alcohol and state-dependent learning.

This paper reviews several attempts to demonstrate state-dependent (St.D) effects from alcohol and reports a study in which the subject's state (sober or intoxicated) produces a 'dissociation' decrement in recall performance only when the drug state differed from that under which the original learning took place. Thirty-two subjects were used in a 2 x 2 design with moderate doses of alcohol (mean BAC = 81 mg/100 ml). In a second study, with 16 volunteers, alcohol was administered immediately after learning in order to distinguish between 'stimulus' and 'storage' hypotheses. Greater retention was found for those subjects whose drug states were the same in memory consolidation and retrieval. Thus, an alcohol state effective during the memory consolidation interval following acquisition appears to be a sufficient condition for producing St.D learning. In this context, St.D learning might be better termed state-dependent memory storage and retrieval. The implications of these results for the aetiology and treatment of alcohol dependence are discussed.

Adult↗
PubMed1982

The stereochemical course of nucleotidyl transfer catalyzed by ATP sulfurylase.

ATP sulfurylase catalyzes the synthesis of ATP from adenosine 5'-phosphosulfate and magnesium pyrophosphate with inversion of configuration at phosphorus. This implies an "in line" displacement mechanism in the ternary complex and effectively eliminates both an adjacent mechanism followed by pseudorotation and a double displacement mechanism involving an adenylyl-enzyme intermediate. The double displacement mechanism had been invoked previously to account for a number of observations, including the ability of the enzyme to catalyze the hydrolysis of MgATP to AMP and MgPPi, and the exchange of Mg32PPi into MgATP in the absence of sulfate.

Adenosine Monophosphate↗
PubMed1982

A stereochemical investigation of the hydrolysis of cyclic AMP and the (Sp)-and (Rp)-diastereoisomers of adenosine cyclic 3':5'-phosphorothioate by bovine heart and baker's-yeast cyclic AMP phosphodiesterases.

Bovine heart cyclic AMP phosphodiesterase, which has a requirement for Mg2+, hydrolyses cyclic AMP with inversion of configuration at the phosphorus atom, but only the (Sp)-diastereoisomer of adenosine cyclic 3':5'-phosphorothioate is hydrolysed by this enzyme. By contrast, the low-affinity yeast cyclic AMP phosphodiesterase, which contains tightly bound Zn2+, hydrolyses both the (Sp)- and the (Rp)-diastereoisomers of adenosine cyclic 3':5'-phosphorothioate, the (Rp)-diastereoisomer being the preferred substrate under V max. conditions. Both of the diastereoisomers of adenosine cyclic 3':5'-phosphorothioate, as well as cyclic AMP, are hydrolysed with inversion of configuration at the phosphorus atom by the yeast enzyme. It is proposed that, with both enzymes, the bivalent metal ion co-ordinates with the phosphate residue of the substrate, and that hydrolysis is catalysed by a direct "in-line' mechanism.

3',5'-Cyclic-AMP Phosphodiesterases↗