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Biomedical subjects

J E Bell

Publications and source records attributed to J E Bell.

At least 127 records · Page 7Linked to original sources
PubMed1984

Effects of phospholipid surface charge on ion conduction in the K+ channel of sarcoplasmic reticulum.

Single-channel K+ currents through sarcoplasmic reticulum K+ channels were compared after reconstitution into planar bilayers formed from neutral or negatively charged phospholipids. In neutral bilayers, the channel conductance saturates with K+ concentration according to a rectangular hyperbola, with half-saturation at 40 mM K+, and maximum conductance of 220 pS. In negatively charged bilayers (70% phosphatidylserine/30% phosphatidylethanolamine), the conductance is, at a given K+ concentration, higher than in neutral bilayers. This effect of negative surface charge is increasingly pronounced at lower ionic strength. The maximum conductance at high K+ approaches 220 pS in negative bilayers, and the channel's ionic selectivity is unaffected by lipid charge. The divalent channel blocker " bisQ11 " causes discrete blocking events in both neutral and negatively charged bilayers; the apparent rate constant of blocking is sensitive to surface charge, while the unblocking rate is largely unaffected. Bilayers containing a positively charged phosphatidylcholine analogue led to K+ conductances lower than those seen in neutral bilayers. The results are consistent with a simple mechanism in which the local K+ concentration sensed by the channel's entryway is determined by both the bulk K+ concentration and the bulk lipid surface potential, as given by the Gouy-Chapman model of the electrified interface. To be described by this approach, the channel's entryway must be assumed to be located 1-2 nm away from the lipid surface, on both sides of the membrane.

Animals↗
PubMed1984

Preparing the P & T committee agenda for new drug requests.

Preparing an agenda is an important element in conducting an effective P & T Committee meeting. A key responsibility of P & T Committee members is reviewing the rationale for formulary requests. Therefore, it is generally an agenda item. This article describes a process for planning, preparing, and distributing agenda materials for a committee meeting. A specific format and sequence for reviewing new drugs for formulary admission and criteria for selecting new drugs are discussed.

Formularies, Hospital as Topic↗
PubMed1983

Glutamate dehydrogenase in Reye's syndrome. Evidence for the presence of an altered enzyme in serum with increased susceptibility to inhibition by GTP.

The glutamate dehydrogenase activity found in the serum of patients with Reye's syndrome is shown to be inhibited about 1000-fold more potently by GTP than is the normal human enzyme. 1 mM ADP, which with the normal enzyme effectively reverses GTP inhibition, has no effect in the GTP inhibition of the Reye's syndrome serum activity.

Adenosine Diphosphate↗
PubMed1983

Demonstration of the existence, and partial characterization, of a cell-surface beta-hexosaminidase from rat splenocytes.

Rat splenocytes are shown to exhibit cell-surface located beta-N-acetylglucosaminidase and beta-galactosidase activities. Preincubation experiments, solubilization experiments and chemical cross-linking experiments show that these enzymatic activities are indeed cell-surface localized. The solubilization and partial purification of the beta-N-acetylglucosaminidase activity is reported. Kinetic studies of the partially purified material with a variety of competitive inhibitors at several pH values suggest that at physiological pH the cell surface beta-N-acetylglucosaminidase may function as a carbohydrate binding protein rather than as a glycosidase.

Animals↗
PubMed1983

A steady-state random-order mechanism for the oxidative deamination of norvaline by glutamate dehydrogenase.

The kinetic mechanism of glutamate dehydrogenase with the monocarboxylic substrate norvaline was examined by using initial-rate steady-state kinetics and inhibition kinetics. To a first approximation the reaction mechanism can be described as a rapid-equilibrium random-order one. Binding synergism between the monocarboxylic substrate and coenzyme is not observed. Dissociation constants for NAD+ and 2-oxoglutarate calculated from the kinetic data assuming a rapid-equilibrium random-order model are in good agreement with independently obtained estimates. Lineweaver-Burk plots with varied norvaline concentration are not strictly linear, and it is concluded that a steady-state random-order model more accurately reflects the observed kinetics with norvaline as substrate.

Animals↗
PubMed1983

Mission, role, and functions of the P & T Committee.

This introductory article in a series on P & T Committees discusses the mission, role, and function of the committee in a hospital. With increasing complexity of drug therapy, the committee's mission has evolved into a multifaceted program related to promotion of rational and safe drug therapy within the institution. Components of the mission, the committee's responsibilities and functions, including formulary, policies and procedures, drug utilization review, drug administration, investigational drug studies, and education, are introduced and briefly discussed in terms of their role in the institution, accreditation standards, and published standards of practice. Future articles will provide fuller consideration of these topics.

Drug Therapy↗
PubMed1982

Regulation of bovine glutamate dehydrogenase. The effects of pH and ADP.

The activity of bovine liver glutamate dehydrogenase is affected in several ways depending on substrate concentrations and pH. At ph 6.5 and below, both oxidative deamination and reductive amination reactions are inhibited by ADP. At pH 7.0 and above both activatory and inhibitory effects can be observed depending on substrate concentrations. The effects are explicable in terms of a model with ADP binding at both a regulatory site and competing with coenzyme at the active site. The activatory effects of ADP result from destabilization of various abortive complexes by ADP binding to its regulatory site. The concerted effects of pH and ADP lead to a potentiation of either activation effects or inhibition effects depending on conditions. A consideration of in vivo concentrations of the various substrates involved and intramitochondrial pH and adenine nucleotide levels suggests that in vivo the reductive amination reaction is favored. It is suggested that glutamate dehydrogenase may be intimately involved with regulation of the urea cycle by responding to changes in the mitochondrial ammonia levels.

Adenosine Diphosphate↗
PubMed1982

Mechanism of hysteresis in bovine glutamate dehydrogenase: role of subunit interactions.

Hysteresis in glutamate dehydrogenase is observed only in the reductive amination reaction and only with GTP present. The rate of reductive amination with NADH as coenzyme increases during the time course of the reaction. Premixing experiments, where glutamate dehydrogenase is preincubated with various combinations of substrates and GTP, suggest that the hysteresis phenomenon is not due to a time-dependent conformational change in the enzyme. Enzyme dilution experiments show (i) that the hysteresis is not due to enzyme association-dissociation effects and (ii) that the onset of the activation occurs after accumulation of about 25 microM NAD+. Addition of NAD+ to the initial reaction mixture prevents hysteresis from occurring. Although with NADPH as coenzyme hysteresis does not occur, addition of NADP+ to initial reaction mixtures containing NADH blocks hysteresis. A model based on reciprocating subunits is proposed whereby hysteresis results from product (NAD+) accumulation resulting in a half-of-the-sites activation of reductive amination.

Animals↗
PubMed1982

Studies on the area cerebrovasculosa of anencephalic fetuses.

The area cerebrovasculosa has been examined in 35 anencephalic fetuses and coronal sections prepared in 15 cases. A bilaterally symmetrical cystic mass is found covering the anterior and middle cranial fossae. The mass is generally walled with glial tissue, partially lined with ependyma and filled with abnormally vascular choroid plexus. The coverings of the cyst are conspicuously vascular and the overlying squamous epithelium is in continuity with hairy skin at the margins of the lesion. The posterior cranial fossa contains a variable quantity of medulla oblongata which has no connection with the cystic mass. The medulla and cervical cord are more nearly normal in that minority of cases with an intact foramen magnum. The degree of hindbrain development is correlated with previously reported presence of heterotopic glial tissue in the spinal subarachnoid space of some anencephalic fetuses (Bell, Gordon and Maloney, 1981; Bell, 1981, in press). These findings have led us to reject the widely accepted view that the area cerebrovasculosa is totally disorganised, and that anencealy is characterised by absence of the forebrain.

Anencephaly↗
PubMed1981

Abnormalities of the spinal meninges in anencephalic fetuses.

The spinal cord and meninges were examined, at all levels, in seven anencephalic fetuses of between 19 and 24 weeks of gestation. Four of the seven anencephalics showed dense collections of cells resembling immature neural tissue throughout the spinal subarachnoid space. The leptomeninges were excessively vascular and contained many active macrophages and small round cells in all the anencephalics and the cord was more slender than normal. Control fetuses did not show these features, although inactive macrophages were seen occasionally. It is concluded that the abnormal collections are made up of heterotopic neural tissue which may have been dislodged downwards from the skull during earlier development and that the spinal leptomeninges show an inflammatory response. The significance of both the heterotopia and the phagocytic activity in these anencephalic fetuses is discussed. In particular, the findings are compared with those in patients with the "respirator brain" syndrome, in whom displacement of brain tissue is associated with raised intracranial pressure.

Anencephaly↗
PubMed1980

Effects of adenosine 5'-diphosphate on bovine glutamate dehydrogenase: diethyl pyrocarbonate modification.

Initial rate kinetic studies and reduced coenzyme binding studies with bovine glutamate dehydrogenase have shown that an enzyme-NAD(P)H-glutamate abortive complex is a major participant in the overall enzyme-catalyzed reaction. The allosteric regulator ADP is shown to activate the enzyme by destabilizing this abortive complex. Destabilization of this abortive complex with concomitant activation is also achieved by the ethoxyformylation of a single histidine residue per subunit in the hexameric enzyme. ADP, in addition to its activatory effects, is shown to (a) remove the nonlinearity from the Lineweaver-Burk plots which is attributable to negative cooperativity and (b) inhibit the enzyme as a competitive inhibitor with respect to coenzyme under the appropriate conditions. Ethoxyformylation with diethyl pyrocarbonate, which mimics the activatory effects of ADP, has no effect on the negative cooperativity shown by this enzyme. A model for the action of ADP is proposed in which ADP activates glutamate dehydrogenase by binding to a regulatory binding site and blocks the negative cooperativity by mimicking the natural coenzyme at the active site of the enzyme.

Adenosine Diphosphate↗
PubMed1980

Dual nucleotide specificity of bovine glutamate dehydrogenase. The role of negative co-operativity.

The thionicotinamide analogues of NAD+ and NADP+ were shown to be good alternative coenzymes for bovine glutamate dehydrogenase, with similar affinity and approx. 40% of the maximum velocity obtained with the natural coenzymes. Both thionicotinamide analogues show non-linear Lineweaver-Burk plots, which with the natural coenzymes have been attributed to negative co-operativity. Since the reduced thionicotinamide analogues have an isosbestic point at 340nm and have an absorption maximum at 400nm, it is possible to monitor reduction of natural coenzyme and thionicotinamide analogue simultaneously by dual-wavelength spectroscopy. When glutamate dehydrogenase is presented with NADP+ and thio-NADP+ simultaneously, the enzyme oligomer senses saturation of its coenzyme-binding sites irrespective of the exact nature of the coenzyme and locks the oligomer into its highly saturated form even when low saturation of the monitored coenzyme is present. These experiments substantiate the suggestion that glutamate dehydrogenase shows negative co-operativity in its catalytically active form.

Animals↗
PubMed1980

Active site of bovine galactosyltransferase: kinetic and fluorescence studies.

Bovine galactosyltransferase has been shown to have two metal binding sites. The functional properties of these metal binding sites have been established by using kinetic, spectroscopic, and affinity chromatographic approaches. Metal site I, which is involved in maintaining the structural integrity of the protein, must be liganded prior to other substrates binding and prior to a second metal binding to site II, which is shown to be associated with UDP-galactose binding. Both metal sites can bind a variety of metals; however, calcium and its fluorescent analogue europium bind only to site II. Fluorescent resonance energy transfer measurements between europium in site II and cobalt in site I indicate a distance of 18 +/- 3 A between the two sites. Chemical modification studies with S-mercuric-N-dansylcysteine indicate that one (of a total of three exposed sulfhydryl groups) can be specifically dansylated and that this sulfhydryl group is in or near the UDP-galactose binding site. Resonance energy transfer measurements between this introduced sulfhydryl group and cobalt in metal site I give a distance of 19 +/- 3 A between these points, consistent with the interpretation that the UDP-galactose binding site, which is associated with metal site II, is located some distance from the structural metal site (site I).

Acetylglucosamine↗
PubMed1980

Bovine galactosyltransferase: interaction with alpha-lactalbumin and the role of alpha-lactalbumin in lactose synthase.

Bovine alpha-lactalbumin has been dansylated to give an enzymatically fully active, highly fluorescent derivative. This derivative is uniquely labeled on the N-terminal glutamic acid residue of alpha-lactalbumin. This fluorescent derivative of alpha-lactalbumin has been covalently cross-linked to galacto-syltransferase by using dimethyl pimelimidate. Resonance energy transfer measurements using cobalt bound to the transferase as the acceptor of energy transfer from the dansyl group on the alpha-lactalbumin indicate that the dansyl group is 32 A from the cobalt of the transferase. A model of the active site of the transferase and its interaction with alpha-lactalbumin is proposed on the basis of these and previous studies.

Animals↗
PubMed1979

Fused suprarenal glands in association with central nervous system defects in the first half of foetal life.

Fifty-two abortuses with CNS defects, delivered during the first half of gestation, were examined for the presence of fused suprarenal glands. Three cases were found, the first in an 8 week embryo aborted spontaneously; the second and third in 18 and 20-week foetuses terminated for suspected CNS abnormality. All three had severe vertebral pathology in addition to the fused suprarenals and the CNS defects. It is suggested that the anomaly may be part of a widespread embryonal distortion secondary to disturbance in the vertebral axis. Since going to press, a further case of fused suprarenals has been found in a 22 week female foetus which had anencephaly and complete spina bifida, severe scoliosis and kyphosis, a small omphalocele, absence of the right kidney, a polycystic left kidney and a unicornuate uterus. This case was found among 12 further abortuses with CNS defects.

Adrenal Glands↗