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Biomedical subjects

L C Davis

Publications and source records attributed to L C Davis.

At least 19 recordsLinked to original sources
PubMed1993

Sideport incision paracentesis versus antiglaucoma medication to control postoperative pressure rises after intraocular lens surgery.

Twenty-eight patients who had an intraocular pressure greater than 30 mm Hg within 24 hours after cataract surgery were randomly assigned to be treated with medication or by paracentesis through a sideport incision. Paracentesis provided an immediate reduction in intraocular pressure, but within one hour pressures rebounded. Within two to three hours after treatment, the medication group had significantly greater mean reductions in intraocular pressure than the paracentesis group.

Acetazolamide↗
PubMed1992

Systematics and body size: implications for feeding adaptations in New World monkeys.

The relationship between body size and feeding ecology is well established for primates. It is argued that the evolutionary history of modern New World monkeys and, in particular, the path to attainment of current body size is significant in understanding the similarities and differences between dietary strategies and other ecological parameters of similar-sized monkeys. Current interpretations of New World monkey evolutionary relationships are reviewed. Based on a synthesis of available body weights and the assumption that the earliest New World monkeys weighed close to 1 kg, similar to modern Aotus and Callicebus, predicted patterns of body size change in each lineage are given. Restrictions on directions of body size change in primates are discussed, and it is shown that "Stanley's Rule" offers a good explanation for differing body size ranges in New and Old World anthropoids. Predicted ecological correlates to body size drawn from the mammalian literature are offered and tested using data on New World monkeys, which show some concurrence and several interesting departures from predicted patterns. Sexual dimorphism in body weight of New World monkey species is reviewed, based on the new summary of body weight data given.

Adaptation, Physiological↗
PubMed1990

Two-step isolation of bacterial ribonucleic acid without using a chaotropic agent or cesium chloride centrifugation.

A simple RNA isolation method was developed to purify bacterial RNAs from a large number of samples simultaneously in an hour. The method is based on boiling the cells in the presence of Triton X-100 and lysozyme, and then preferential RNA precipitation with ammonium acetate. There is no CsCl centrifugation required. For the nitrogen-fixing bacterium Klebsiella pneumoniae, the depression condition can be maintained during the cell-harvesting process. The intact isolated RNAs appeared to be free of protein, with a yield of 100 micrograms RNA from a 4-ml cell culture of 100 Klett units (10(9) cells/ml). Any DNA present was in a form that did not react with a nifH probe following Northern blotting to nitrocellulose (i.e., was not single-stranded).

Acetates↗
PubMed1990

Kinetics of protease hydrolysis of extended peptide substrates: measurement by flow-injection analysis.

A flow-injection analysis (FIA) system was developed to study the enzyme-catalyzed hydrolysis of synthetic peptides, each of which contained one scissile bond. The concentrations of alpha-amino groups in reactions mixtures were determined by FIA with o-phthalaldehyde as a fluorescence reagent. The method allows a rapid, precise, and sensitive determination of kinetic constants for proteases acting on extended peptide substrates.

Chromatography, High Pressure Liquid↗
PubMed1989

Substitution of histidine for arginine-101 of dinitrogenase reductase disrupts electron transfer to dinitrogenase.

Dinitrogenase reductase from Klebsiella pneumoniae strain UN1041 has a histidine residue substituted for arginine at position 101. The mutant dinitrogenase reductase was purified and characterized in order to determine the importance of arginine-101 in the interaction between dinitrogenase and dinitrogenase reductase during electron transfer. Purified dinitrogenase reductase from UN1041 is a dimer of 67 kDa, contains a functional 4Fe-4S cluster, undergoes a MgATP-dependent conformational change, and is competent for ATP hydrolysis uncoupled from substrate reduction in the presence of dinitrogenase. However, the mutant protein is unable to support the reduction of protons or acetylene by dinitrogenase. A 100-fold molar excess of Kp2 from UN1041 does not inhibit electron transfer from wild-type dinitrogenase reductase to dinitrogenase. It is concluded that the interaction of dinitrogenase reductase with dinitrogenase during reductant-independent ATP hydrolysis is different than the interaction between the two proteins during electron transfer; the substitution of histidine for arginine at position 101 disrupts only the latter interaction. The same conclusions are reached using wild-type dinitrogenase reductase which has been ADP-ribosylated at arginine-101.

Adenosine Triphosphate↗
PubMed1989

Estimation of nitrogenase activity in the presence of ethylene biosynthesis by use of deuterated acetylene as a substrate.

Nitrogenase reduces deuterated acetylene primarily to cis dideuterated ethylene. This can be distinguished from undeuterated ethylene by the use of Fourier transform infrared spectroscopy. Characteristic bands in the region from 800 to 3,500 cm-1 can be used to identify and quantitate levels of these products. This technique is applicable to field studies of nitrogen fixation where ethylene biosynthesis by plants or bacteria is occurring. We have verified the reaction stoichiometry by using Klebsiella pneumoniae and Bradyrhizobium japonicum in soybeans. The most useful bands for quantitation of substrate purity and product distribution are as follows: acetylene-d0, 3,374 cm-1; acetylene-d1, 2,584 cm-1; acetylene-d2, 2,439 cm-1; cis-ethylene-d2, 843 cm-1; trans-ethylene-d2, 988 cm-1; ethylene-d1, 943 cm-1; ethylene-d0, 949 cm-1. (The various deuterated ethylenes and acetylenes are designated by a lowercase d and subscript to indicate the number, but not the position, of deuterium atoms in the molecule.) Mass spectrometry coupled to a gas chromatograph system has been used to assist in quantitation of the substrate and product distributions. Significant amounts of trans-ethylene-d2 were produced by both wild-type and nifV mutant K. pneumoniae. Less of this product was observed with the soybean system.

Acetylene↗
PubMed1988

Characterization of nifH mutations of Klebsiella pneumoniae.

Nucleotide changes in the nifH gene of Klebsiella pneumoniae were identified by DNA cloning and sequencing of six selected mutant strains. The strains were UN60, C-640-GC----TGC; UN116, C-67-TC----TTC; UN117, G-688-AG----AAG; UN1041, CG-302-C----CAC; UN1678, GC-713-C----GTC; and UN1795, G-439-AG----AAG. Their corresponding amino acid substitutions were UN60, Arg-214----Cys; UN116, Leu-23----Phe; UN117, Glu-230----Lys; UN1041, Arg-101----His; UN1678, Ala-238----Val; and UN1795, Glu-147----Lys. Results from Western and Northern blots of the mutant strains showed significant reductions in both steady-state levels of the accumulated Fe protein and nifH mRNA during derepression in the presence of serine. The relative specific activities of the nitrogenases in strains UN60, UN1041, and UN1795 were less than 2% of the wild type, whereas those in UN116, UN117, and UN1678 were between 28 and 40% of the wild type during enhanced derepression with serine. The residues of Arg-101 (UN1041), Glu-147 (UN1795), and Arg-214 (UN60) were invariant in sequences of a dozen diazotrophs that have been examined thus far. In UN1041, in which Arg-101 of the Fe protein was replaced by His, the Fe protein had a larger apparent molecular weight than that of the other strains on sodium dodecyl sulfate-gel electrophoresis, as detected with rabbit antiserum raised against the C-terminal peptide of the wild-type Fe protein. The reduced levels of nifH mRNA in point mutant strains suggests that nifH (the gene or gene product) may be involved in self-regulation. mRNA transcripts of different sizes were detected when a nifH-specific probe, CCKp2003, was used in the Northern blot hybridization.

DNA, Bacterial↗
PubMed1987

Measurement of protein using flow injection analysis with bicinchoninic acid.

We have used the bicinchoninic acid reagent developed by Pierce Chemical Co. to measure proteins in a simple flow injection analyzer. The sensitivity is comparable to that of the Lowry method and no pipetting of reagents is needed. Results are obtained in less than 1 min and samples may be run at a rate of 60/h. The response is linear over a range of protein concentration (0-10 micrograms) and sample size (5-20 microliters) convenient for most analytical requirements. A peristaltic pump, a controlled-temperature water bath, and a spectrophotometer with flow cuvette are the only special apparatus required.

Proteins↗
PubMed1986

C-terminal peptides of rhodopsin. Determination of the optimum sequence for recognition of retinal transducin.

In vertebrate retinal rod outer segments, transducin, a guanine-nucleotide-binding protein, mediates signal coupling between rhodopsin and cyclic GMP phosphodiesterase. Whereas the T alpha subunit (39 kDa) of transducin binds guanine nucleotides and is the activator of the phosphodiesterase, the T beta gamma subunits (35 and 10 kDa) may function to physically link T alpha with photolysed rhodopsin. We have previously reported that a site of binding of transducin is on the C-terminus of bovine rhodopsin. By using competition with synthetic peptides, the recognition region was localized to bovine opsin amino acid residues 317-339. Further studies are detailed which determine the boundaries of this binding site on rhodopsin, as well as some of the critical amino acids needed for transducin binding. These results suggest that the serine and threonine residues in the rhodopsin C-terminal peptides Rhod-1 and Rhod-3 are critical for reconstitution of transducin GTPase activity.

Amino Acid Sequence↗
PubMed1984

Chemically coupled spectrophotometric assays based on flow injection analysis: determination of nitrogenase by assays for creatine, ammonia, hydrazine, phosphate, and dithionite.

Micromethods of direct chemical coupling have been developed for several different enzyme reactions, using the principles of flow injection analysis. Samples of 1-25 microliters are injected into a flowing stream of color-forming reagents and the peak of color change is measured after about 1 min. Alternatively, continuous slow infusion of a reacting system (5-100 microliters/min) gives a continuous change of color which can be monitored to derive enzyme reaction rates. These techniques are highly sensitive, requiring a few nanomoles of the substance being detected. Phosphate, ammonia, dithionite, creatine, and hydrazine have been measured. Consumption of reagents is less than 75 ml per hour; typical sample throughout is 30-40 samples per hour by the injection method, and 5 samples per hour by continuous infusion. The procedure has been applied to nitrogenase, continuously monitoring creatine produced from creatine phosphate by creatine kinase which is used to supply a constant level of ATP for nitrogenase. In this way nitrogenase activity can be determined over a wide range of enzyme concentrations. Production of inorganic phosphate directly from ATP, by injection of formaldehyde-quenched samples, was used when coupling to creatine kinase was not possible. Both injection of aliquots and continuous infusion were used for detection of hydrazine during nitrogenase reduction of azide, and the injection method has been used for ammonia assay during dinitrogen reduction. Dithionite oxidation was measured directly from decolorization of iodine, after trapping both dithionite and bisulfite with formaldehyde.

Ammonia↗
PubMed1983

Training community-based, Asian-American mental health personnel in behavior modification.

Sixteen Asian-American and Pacific Island mental health professionals received 10 weekly, 2-hour training sessions on behavior modification and its application, in particular, to Asian-American clients. A three-fold assessment of the training results revealed: a) a significant increase in knowledge of behavior modification principles, b) a significant increase in ability to accomplish a behavioral analysis and behavioral treatment plan, and c) a significant increase in one of three attitudes toward behavior modification: oriented activity. In general, the training was rated highly and, perhaps more importantly, was viewed as having relevance for this particular minority population which often under utilizes mental health services. The training model and needs for further consultation and supervision were discussed.

Asian↗
PubMed1983

Interaction of nitrogenase with nucleotide analogs of ATP and ADP and the effect of metal ions on ADP inhibition.

The interaction of a large number of ATP and ADP analogs with nitrogenase from Azotobacter vinelandii, Klebsiella pneumoniae, and Clostridium pasteurianum has been examined. Only 1,N6-etheno-ATP and 2'-deoxy-ATP served as substrates for acetylene reduction. Other triphosphates including GTP, ITP, 8-Br-ATP, alpha,beta-methylene ATP, beta,gamma-methylene ATP, 6-chloropurine riboside triphosphate, and AMP-PNP were inert, showing less than 50% inhibition at levels up to two- to fivefold greater than ATP. Xanthosine triphosphate behaved simply as a chelator of magnesium, activating the enzyme at low levels but strongly inhibiting at high levels. When nucleotide diphosphates were tested as inhibitors with enzyme from A. vinelandii, GDP, dGDP, and 6-chloropurine riboside diphosphate were ineffective, XDP was three- to fivefold less effective, and dADP and 1,N6-etheno-ADP were about equally as effective as ADP. With enzyme from C. pasteurianum, dADP was twofold less effective than ADP, XDP was fivefold less effective, and IDP and 1,N6-etheno-ADP appeared to be ineffective. Results with enzyme from K. pneumoniae were very similar to those obtained with A. vinelandii. Different metal ions were tested in the presence of both ATP and ADP to determine whether preferential binding to one nucleotide or the other might alter the ADP/ATP ratio needed for 50% inhibition of activity. Magnesium and manganese gave the same ratio, while with Fe and Co, slightly less ADP was required for equivalent inhibition. Nickel appeared to reduce the sensitivity of A. vinelandii nitrogenase to ADP inhibition while increasing that of C. pasteurianum, but both effects were less than twofold. Calcium, strontium, and aluminum ions were inert with enzymes from these organisms. Cd and Zn were also ineffective with K. pneumoniae. Two isomers of ATP beta S were prepared by enzymatic synthesis from ADP beta S. The A form was a more potent inhibitor of A. vinelandii nitrogenase.

Adenosine Diphosphate↗
PubMed1983

Training Mexican American mental health personnel in behavior therapy.

Fourteen Mexican American mental health workers were trained in basic behavior therapy principles and behavior contracting in 10 weekly, 2 hr sessions. A significant increase was found in knowledge of principles, and attitudes toward behavior therapy became more positive. In addition, clinical skill in doing a behavior analysis and formulating a behavior therapy plan also improved. A 6 month follow-up suggested continued application of training. Results and match of behavior therapy training to differing cultures are discussed.

Behavior Therapy↗
PubMed1983

Broad-zone active-enzyme chromatography. Keto-acid dehydrogenases as associating systems.

We have extended the method of active-enzyme chromatography to include the use of broad zones of enzyme. This allows examination of interacting systems in a way formally analogous to sedimentation velocity so that simulation of the observed activity profiles is possible. The method has been applied using pyridine nucleotide-linked active enzyme assays. At the concentrations presently accessible by this technique, hexokinase and glucose-6-phosphate dehydrogenase, both associating systems, show single symmetrical boundaries, as does isolated diaphorase, while pyruvate and alpha-ketoglutarate dehydrogenases show more complex patterns, with the position of the reaction boundary for diaphorase activity being dependent on enzyme concentration.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗