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D L Martin

Publications and source records attributed to D L Martin.

At least 91 records · Page 5Linked to original sources
PubMed1988

Characterization of Alkaloid Uptake by Catharanthus roseus (L.) G. Don Protoplasts.

The accumulation of alkaloids by protoplasts of Catharanthus roseus (L.) G. Don var. Little Bright Eye was studied to determine the specificity of uptake and the role of ion trapping in the storage of alkaloids. Accumulation of the indole alkaloids vindoline, ajmalicine, tabersonine, and vinblastine was found to be biphasic, with an initial burst of uptake followed by a slow, prolonged phase of accumulation. The concentration and pH dependence of the initial burst of uptake for vindoline suggested that uptake occurred by simple diffusion. Uptake of nicotine was monophasic, with a half life of 5.2 minutes. The accumulation ratio (Ci/Ce) for nicotine at steady state and for the initial burst of uptake for vindoline and ajmalicine suggested that accumulation was driven by the pH gradient between the vacuole and the external assay medium. The second, sustained phase of uptake of vindoline was sensitive to inhibition by either 20 millimolar NaN(3) or 0.5 millimolar Cu(2+). In azide-treated protoplasts, the uptake for vindoline conformed to the kinetics of simple diffusion, with a half life of 4 minutes. The second phase of uptake for ajmalicine, although sensitive to inhibition by Cu(2+), was insensitive to inhibition by NaN(3). The biphasic uptake of the indole alkaloids was not due to any significant metabolism. It is concluded that accumulation and storage of the indole alkaloids is due only partly to ion trapping of the alkaloids by the low pH of the vacuole lumen. In the case of vindoline, there appears to be a specific energy-requiring uptake that is not seen with nicotine (which is not endogenous to Catharanthus). Accumulation of ajmalicine appears to involve both ion trapping and an azide-insensitive component, which may be due to complexation with organic counterions and phenolics.

Journal Article↗
PubMed1988

Stability and activation of glutamate apodecarboxylase from pig brain.

The stability and activation of glutamate apodecarboxylase was studied with three forms of the enzyme from pig brain (referred to as the alpha, beta, and gamma forms). Apoenzyme was prepared by incubating the holoenzyme with aspartate followed by chromatography on Sephadex G-25. Apoenzyme was much less stable than holoenzyme to inactivation by heat (for beta-glutamate decarboxylase (beta-GAD) at 30 degrees C, t1/2 values of apo- and holoenzyme were 17 and greater than 100 min). ATP protected holoenzyme and apoenzyme against heat inactivation. The kinetics of reactivation of apoenzyme by pyridoxal-P was consistent with a two-step mechanism comprised of a rapid, reversible association of the cofactor with apoenzyme followed by a slow conversion of the complex to active holoenzyme. The reactivation rate constant (kr) and apparent dissociation constant (KD) for the binding of pyridoxal-P to apoenzyme differed substantially among the forms (for alpha-, beta-, and gamma-GAD, kr = 0.032, 0.17, and 0.27 min-1, and KD = 0.014, 0.018, and 0.04 microM). ATP was a strong competitive inhibitor of activation (Ki = 0.45, 0.18, and 0.39 microM for alpha-, beta-, and gamma-GAD). In contrast, Pi stimulated activation at 1-5 mM but inhibited at much higher concentrations. The results suggest that ATP is important in stabilizing the apoenzyme in brain and that ATP, Pi, and other compounds regulate its activation.

Adenosine Triphosphate↗
PubMed1987

Kinetically different, multiple forms of glutamate decarboxylase in rat brain.

Four molecular forms of rat-brain glutamate decarboxylase were resolved by hydrophobic interaction chromatography on phenyl-Sepharose and affinity chromatography on ATP-agarose. SDS-polyacrylamide gel electrophoresis of purified enzyme and immunoblots of SDS gels indicated a subunit molecular weight of approximately 60,000 for each form of the enzyme, and cross-linking with dimethyl suberimidate prior to electrophoresis indicated that each form has dimeric subunit structure. Immunoblots of non-denaturing gels showed differing electrophoretic mobilities among the forms. The kinetic properties of the 4 enzyme forms were found to be significantly different. The Km for glutamate ranged from 0.17 +/- 0.05 to 1.18 +/- 0.08 mM, and there was a greater than two-fold range in their rates of inactivation by glutamate and GABA in the absence of pyridoxal 5'-phosphate. In subcellular fractionation experiments the forms with greater electrophoretic mobility were recovered in the synaptosomal fraction, and the form with the lowest electrophoretic mobility was the most abundant in the postmicrosomal supernatant. Calcium-dependent binding of glutamate decarboxylase in crude enzyme preparations to phospholipid vesicles was observed, but none of the purified enzyme forms showed an appreciable degree of binding to the vesicles.

Animals↗
PubMed1987

Cortical bone maintenance in an historic Afro-American cemetery sample from Cedar Grove, Arkansas.

The relocation and analysis of 80 skeletons from the Cedar Grove Cemetery, located in southwest Arkansas, provides an opportunity to examine the level of health and nutrition experienced by Afro-Americans in the post-Reconstruction South (1878-1930). The demographic profile lends support to the interpretation that Cedar Grove participated in the nationwide decline in Afro-American health. The high frequencies of skeletal lesions indicative of dietary deficiencies and infectious disease demonstrate that this was a highly stressed population. For this analysis, adult femoral thin sections (15 females and 14 males) are examined histologically. These data provide support to the assertion that the Cedar Grove population experienced poor health. Measures taken from the sections include cortical thickness, percent cortical area, and mean number of resorption spaces and forming osteons per square millimeter of bone. As a group, they demonstrate low percent cortical area compared with well-nourished normals. They also show high rates of resorption to formation, thereby disrupting the balance necessary for normal cortical bone maintenance. The pattern established for bone porosity in this group is not a function of age but rather is due to other factors, most likely nutrition and disease stress. What may be unique about this group is that males, as well as females, experienced problems with calcium homeostasis and normal maintenance and repair of bone. Taken together, these data support the interpretation that diet and health were substandard in the post-Reconstruction South.

Black or African American↗
PubMed1987

Regulatory properties of brain glutamate decarboxylase.

1. Glutamate decarboxylase is a focal point for controlling gamma-aminobutyric acid (GABA) synthesis in brain. Several factors that appear to be important in the regulation of GABA synthesis have been identified by relating studies of purified glutamate decarboxylase to conditions in vivo. 2. The interaction of glutamate decarboxylase with its cofactor, pyridoxal 5'-phosphate, is a regulated process and appears to be one of the major means of controlling enzyme activity. The enzyme is present in brain predominantly as apoenzyme (inactive enzyme without bound cofactor). Studies with purified enzyme indicate that the relative amounts of apo- and holoenzyme are determined by the balance in a cycle that continuously interconverts the two. 3. The cycle that interconverts apo- and holoenzyme is part of the normal catalytic mechanism of the enzyme and is strongly affected by several probable regulatory compounds including pyridoxal 5'-phosphate, ATP, inorganic phosphate, and the amino acids glutamate, GABA, and aspartate. ATP and the amino acids promote apoenzyme formation and pyridoxal 5'-phosphate and inorganic phosphate promote holoenzyme formation. 4. Numerous studies indicate that brain contains multiple molecular forms of glutamate decarboxylase. Multiple forms that differ markedly in kinetic properties including their interactions with the cofactor have been isolated and characterized. The kinetic differences among the forms suggest that they play a significant role in the regulation of GABA synthesis.

Adenosine Triphosphate↗
PubMed1987

Reuse of disposable medical devices in Canadian hospitals.

A survey of all Canadian hospitals was undertaken in 1986 to determine the extent of the reuse of disposable medical devices meant for "single use only." It was found that 41% of hospitals regularly reused disposable medical devices, and reuse was significantly higher in hospitals with more than 200 beds. Only 38% of hospitals that regularly reused had written procedures for reuse, and 32% indicated a mechanism for determining the number of times a device was reused. Cost analysis studies had been undertaken by only 29% of regular reusers, and items of respiratory therapy equipment were the most commonly reused devices.

Canada↗
PubMed1987

Rapid inactivation of brain glutamate decarboxylase by aspartate.

In the absence of its cofactor, pyridoxal 5'-phosphate (pyridoxal-P), glutamate decarboxylase is rapidly inactivated by aspartate. Inactivation is a first-order process and the apparent rate constant is a simple saturation function of the concentration of aspartate. For the beta-form of the enzyme, the concentration of aspartate giving the half-maximal rate of inactivation is 6.1 +/- 1.3 mM and the maximal apparent rate constant is 1.02 +/- 0.09 min-1, which corresponds to a half-time of inactivation of 41 s. The rate of inactivation by aspartate is about 25 times faster than inactivation by glutamate or gamma-aminobutyric acid (GABA). Inactivation is accompanied by a rapid conversion of holoenzyme to apoenzyme and is opposed by pyridoxal-P, suggesting that inactivation results from an alternative transamination of aspartate catalyzed by the enzyme, as previously observed with glutamate and GABA. Consistent with this mechanism pyridoxamine 5'-phosphate, an expected transamination product, was formed when the enzyme was incubated with aspartate and pyridoxal-P. The rate of transamination relative to the rate of decarboxylation was much greater for aspartate than for glutamate. Apoenzyme formed by transamination of aspartate was reactivated with pyridoxal-P. In view of the high rate of inactivation, aspartate may affect the level of apoenzyme in brain.

Animals↗
PubMed1987

Commercial feasibility of embryo transfer technology: a case study.

The owner of a 500-cow Holstein herd requested economic assessment of his embryo transfer program. Actual net economic benefit was determined from marginal cost and present value of lifetime milk predicted from first lactations of 24 cows produced by embryo transfer compared with those of their 51 contemporaries sired by artificial insemination. Actual average pregnancy rate was 60% by embryo transfer or AI. An average of 5.5 transferable embryos was obtained per collection, which produced 1.37 cows in first lactation. Additional milk from embryo transfer cows was from more intensive selection of sires. Additional milk from the donor cows did not differ from zero. Actual marginal cost of a replacement by embryo transfer was +215, but it would have been +200 with same +25/unit semen price as contemporaries. If donors had been from the elite 5% for transmitting ability in milk, present value of gain in milk (5% real interest rate) ignoring additional feed costs would have been less than the cost of embryo transfer. For management and costs similar to this case, embryo transfer is not economically justified for producers earning income primarily from the sale of milk.

Animal Husbandry↗
PubMed1986

Non-steady-state kinetics of brain glutamate decarboxylase resulting from interconversion of the apo- and holoenzyme.

In addition to its primary reaction, brain glutamate decarboxylase (L-glutamate 1-carboxy-lyase, EC 4.1.1.15) catalyses an alternative transamination reaction that leads to the production of apoenzyme. Apoenzyme can be converted to holoenzyme by reaction with pyridoxal 5'-phosphate, thereby completing a cyclic interconversion of the apo- and holoenzyme. The effect of the cycle on the kinetic behavior of the enzyme was investigated with the aid of a kinetic model that combines a steady-state description of the primary reaction and a non-steady-state description of the cycle. In the presence of saturating levels of the cofactor, pyridoxal 5'-phosphate, the cycle had little effect on the kinetics of slowly transaminated substrates such as glutamate. However, the kinetic behavior of aspartate, a rapidly transaminated substrate, was strongly affected by the cycle. With aspartate, a large proportion of apoenzyme was produced, resulting in non-linear decarboxylation time courses. Estimates of the steady-state kinetic parameters for aspartate (Km, Ki, Vmax) and the apparent type of inhibition were found to depend strongly on the assay time and procedure. Similar dependencies were found for the aspartate analogues, methyl alpha-DL-aspartate, cysteine sulfinate and beta-alanine, suggesting that they also undergo rapid transamination. The kinetic model accurately predicted holoenzyme levels and accurately described the decarboxylation time courses for glutamate, aspartate and mixtures of these substrates.

Animals↗
PubMed1986

A membrane protein in LRM55 glial cells cross-reacts with antibody to the anion exchange carrier of human erythrocytes.

Cl-/HCO3-exchange transport in the glial plasma membrane is remarkably similar to anion exchange transport in erythrocytes. When LRM55 cells were pretreated with the extracellular labeling reagent [125I]iodosulfanilic acid, radioactivity appeared primarily in two bands on denaturing polyacrylamide gels at Mr 70,000 and 30,000. Antibody to the human erythrocyte anion exchanger (Band 3) cross-reacted on immunoblots with an LRM55 band at Mr 68,000. The LRM55 Cl-/HCO3-exchanger may be a component of Mr 68,000 to 70,000.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1986

Sulfate-chloride exchange transport in a glioma cell line.

Transport of SO4(2-) was studied in the glioma cell line LRM55 to determine whether it is mediated by the Cl-/HCO3- exchanger or the K+/Cl- cotransporter previously described in these cells (Wolpaw, E.W. and Martin, D.L. (1984) Brain Res. 297, 317-327). 35SO4(2-) influx was saturable with SO4(2-). External SO4(2-) stimulated 35SO4(2-) efflux, indicating an exchange mechanism. External Cl- was a competitive inhibitor of 35SO4(2-) influx. Internal Cl- stimulated 35SO4(2-) influx and external Cl- stimulated 35SO4(2-) efflux, indicating that Cl- is an exchange substrate for the SO4(2-) carrier. Also, SO4(2-) flux was sensitive to SITS, DIDS and furosemide. However, saturating external SO4(2-) did not inhibit 36Cl- influx and did not inhibit 36Cl- efflux via the Cl-/HCO3- exchanger. Moreover, K+ did not stimulate 36Cl- efflux via the Cl-/HCO3- exchanger. Moreover, K+ did not stimulate 35SO4(2-) influx as it does Cl- influx. These findings indicate that SO4(2-) transport into these cells is mediated by an exchange carrier distinct from both the Cl-/HCO3- exchanger and the K+/Cl- cotransporter. While Cl- is an alternative substrate for the SO4(2-) porter, this carrier is responsible for only a minor fraction of total Cl- flux in these cells.

Animals↗
PubMed1986

Analysis of aspartate and glutamate in human cerebrospinal fluid by high-performance liquid chromatography with automated precolumn derivatization.

A method is described for the analysis of the neuroexcitatory amino acids, aspartate and glutamate, in human cerebrospinal fluid (CSF) by reverse-phase, high-performance liquid chromatography. Fluorescent isoindole derivatives of the amino acids were prepared by reacting the amino acids with ortho-phthalaldehyde in an automated, precolumn procedure. Chromatographic conditions were developed that resolve the isoindole derivatives of aspartate and glutamate from those of at least 10 unidentified components of CSF. Amino acids were reliably quantified in 5-microliter samples of CSF, and deproteinization of the specimens was not required. Furthermore, it was found that deproteinization by precipitation with strong acid can lead to artifactually high measurements of glutamate. The concentrations of free aspartate and glutamate in lumbar CSF from 15 neurologically normal children were 0.30 +/- 0.11 and 0.48 +/- 0.26 microM (mean +/- SD), respectively. The value for glutamate is considerably lower than has been reported in any previous study of human CSF.

Adolescent↗
PubMed1986

Dissociation of locus coeruleus activity and blood pressure. Effects of clonidine and corticotropin-releasing factor.

In order to determine whether pharmacologically-induced alterations in the spontaneous activity of neurons in the locus coeruleus are associated with changes in blood pressure, the activity of the locus coeruleus and blood pressure were recorded simultaneously in anesthetized rats after the administration of agents known to affect both of these parameters. Spontaneous activity of the locus coeruleus was decreased by intracerebroventricular (i.c.v.) administration of both clonidine and St 91, [2,(2,6-diethyl-phenylimino)imidazolidine chloride], a charged analogue of clonidine. However, only clonidine decreased the mean blood pressure after intracerebroventricular administration suggesting that either the receptors mediating decreases in the activity of the locus coeruleus are different to those mediating hypotension, or that St 91 does not distribute to sites involved in the control of blood pressure even after intracerebroventricular administration. Intravenous administration of clonidine, but not of St 91, decreased the activity of the locus coeruleus and produced a prolonged hypotension, thus suggesting a central mechanism for these effects. Both clonidine and St 91 administered intravenously, produced a brief initial period of hypertension which was not associated with consistent changes in the spontaneous activity of the locus coeruleus. Thus, noradrenergic agonists can decrease the activity of the locus coeruleus without affecting blood pressure, and increase blood pressure without affecting the activity of the locus coeruleus. The spontaneous activity of cells in the locus coeruleus was increased by 100% after the intracerebroventricular administration of corticotropin-releasing factor (CRF; 3.0 micrograms).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗