Kinetic characterization of dihydrofolate reductase from Drosophila melanogaster

1990 ◽  
Vol 68 (9) ◽  
pp. 1075-1082 ◽  
Author(s):  
Susan L. Rancourt ◽  
Virginia K. Walker
Keyword(s):  
Drosophila Melanogaster ◽  
Dihydrofolate Reductase ◽  
Competitive Inhibitor ◽  
Structural Features ◽  
Acidic Ph ◽  
Kinetic Characteristics ◽  
Ph Values ◽  
Definition Of ◽  
Organic Mercurials

The kinetic characteristics of a purified insect dihydrofolate reductase (DHFR) have been described. The Km values for the substrate dihydrofolate and the cofactor NADPH have been estimated by primary and secondary Hanes plots to be 0.3 and 5.2 μM, respectively. Drosophila melanogaster DHFR can use folate and NADH at acidic pH values, but at a much lower rate than the preferred substrate and cofactor. Folic acid is a partial competitive inhibitor of Drosophila DHFR (Ki = 0.4 μM) and trimethoprim is a complete competitive inhibitor (Ki = 5.4 μM). Methotrexate binds less tightly to the Drosophila enzyme than to many other DHFRs (Kd = 0.9 nM). Drosophila DHFR is inhibited by KCl and organic mercurials and is slightly activated by urea. These data indicate that Drosophila DHFR has some characteristics which are typical of vertebrate DHFRs and others which are typical of prokaryotic DHFRs. The study of this enzyme, therefore, should aid in the definition of the structural features that are responsible for the kinetic characteristics in different DHFRs.Key words: dihydrofolate reductase, Drosophila melanogaster, methotrexate.

FURTHER CHARACTERIZATION OF GENETIC ELEMENTS ASSOCIATED WITH THE SEGREGATION DISTORTER PHENOMENON IN DROSOPHILA MELANOGASTER

Genetics ◽  
1985 ◽  
Vol 110 (4) ◽  
pp. 671-688
Author(s):  
Cecil B Sharp ◽  
Arthur J Hilliker ◽  
David G Holm
Keyword(s):  
Drosophila Melanogaster ◽  
Chromosome 2 ◽  
Major Focus ◽  
Genetic Components ◽  
Segregation Distorter ◽  
Crossover Analysis ◽  
Radiation Induced ◽  
Definition Of ◽  
The Right

ABSTRACT Segregation Distorter, SD, associated with the second chromosome of Drosophila melanogaster, is known to cause sperm bearing the non-SD homologue to dysfunction in heterozygous males. In earlier studies, using different, independently derived, SD chromosomes, three major loci were identified as contributing to the distortion of segregation ratios in males. In this study the genetic components of the SD-5 chromosome have been the subjects of further investigation, and our findings offer the following information. Crossover analysis confirms the mapping of the Sd locus to a position distal to but closely linked with the genetic marker pr. Spontaneous and radiation-induced recombinational analyses and deficiency studies provide firm support to the notion that the Rsp(Responder) locus lies within the proximal heterochromatin of chromosome 2, between the genetic markers lt and rl and most likely in the heterochromatin of the right arm. The major focus of this study, however, has been on providing a better definition of the genetic properties of the Enhancer of SD [E(SD)]. Our findings place this locus within the region of the two most proximal essential genes in the heterochromatin of the left arm of chromosome 2. Moreover, our analysis reveals a probable association of the E(SD) locus with a meiotic drive independent of that caused by Sd.

Structure of Metallic Glasses: Experiments and Models

1996 ◽  
Vol 51 (9) ◽  
pp. 983-990
Author(s):  
P. Lamparter ◽  
S. Steeb
Keyword(s):  
Metallic Glasses ◽  
Short Range ◽  
Short Range Order ◽  
Structural Features ◽  
Range Order ◽  
Related Individual ◽  
Angle Scattering ◽  
Different Types ◽  
Definition Of

Abstract The topological and the chemical short range order in metallic glasses is discussed by means of representative examples from the systems Ni-P, Ni-B, Nb-Ni, and Dy-Ni. The characterization of the chemical short range order, e.g. in terms of a short range order parameter, depends on the definition of an appropriate hypothetic statistical reference system. The consideration of the size effect is essential. Some structural features of metallic glasses point to relationships with the related individual crystalline phases, whereas other features show that the different types of metallic glasses have certain construction principles in common. Small angle scattering with hydrogenated metallic glasses suggests the presence of extended two-dimensional structures. Reverse Monte Carlo models reveal rather broad distributions of the local structural properties and show that metallic glasses are not built as assemblies of defined structural units.

scholarly journals Characterization of a New DyP-Peroxidase from the Alkaliphilic Cellulomonad, Cellulomonas bogoriensis

Molecules ◽  
2019 ◽  
Vol 24 (7) ◽  
pp. 1208 ◽  
Author(s):  
Mohamed H. Habib ◽  
Henriëtte J. Rozeboom ◽  
Marco W. Fraaije
Keyword(s):  
Crystal Structure ◽  
Escherichia Coli ◽  
Active Site ◽  
Biochemical Characterization ◽  
Sequence Motif ◽  
Acidic Ph ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Ph Values

DyP-type peroxidases are heme-containing enzymes that have received increasing attention over recent years with regards to their potential as biocatalysts. A novel DyP-type peroxidase (CboDyP) was discovered from the alkaliphilic cellulomonad, Cellulomonas bogoriensis, which could be overexpressed in Escherichia coli. The biochemical characterization of the recombinant enzyme showed that it is a heme-containing enzyme capable to act as a peroxidase on several dyes. With the tested substrates, the enzyme is most active at acidic pH values and is quite tolerant towards solvents. The crystal structure of CboDyP was solved which revealed atomic details of the dimeric heme-containing enzyme. A peculiar feature of CboDyP is the presence of a glutamate in the active site which in most other DyPs is an aspartate, being part of the DyP-typifying sequence motif GXXDG. The E201D CboDyP mutant was prepared and analyzed which revealed that the mutant enzyme shows a significantly higher activity on several dyes when compared with the wild-type enzyme.

scholarly journals Subcloning and characterization of the binding domain of fragment B of diphtheria toxin

1993 ◽  
Vol 294 (3) ◽  
pp. 663-666 ◽  
Author(s):  
Q Y Esbensen ◽  
P O Falnes ◽  
S Olsnes ◽  
I H Madshus
Keyword(s):  
Crystal Structure ◽  
Amino Acids ◽  
Diphtheria Toxin ◽  
Binding Domain ◽  
Full Length ◽  
Acidic Ph ◽  
High Affinity ◽  
Ph Values ◽  
Triton X

The binding domain (R domain) of diphtheria toxin as defined from the recently published crystal structure [Choe, Bennett, Fujii, Curmi, Kantardjieff, Collier and Eisenberg (1992) Nature (London) 357, 216-222] was subcloned. The 17 kDa peptide containing amino acids 378-535 from fragment B of diphtheria toxin preceded by the tripeptide Met-His-Gly bound specifically and with high affinity to diphtheria-toxin receptors. It efficiently inhibited the toxicity of full-length toxin. The binding domain entered the detergent phase of Triton X-114 at pH values below 6, indicating that it exposed hydrophobic regions at acidic pH.

Skeletal elements of crinoid echinoderms: High-resolution structural and microanalytical results

1983 ◽  
Vol 41 ◽  
pp. 194-195
Author(s):  
D. F. Blake ◽  
L. F. Allard ◽  
D. R. Peacor
Keyword(s):  
High Resolution ◽  
Marine Invertebrates ◽  
Sea Urchins ◽  
Structural Features ◽  
Sea Stars ◽  
High Resolution Tem ◽  
Relationship Of ◽  
The Relationship ◽  
Insight Into

Echinodermata is a phylum of marine invertebrates which has been extant since Cambrian time (c.a. 500 m.y. before the present). Modern examples of echinoderms include sea urchins, sea stars, and sea lilies (crinoids). The endoskeletons of echinoderms are composed of plates or ossicles (Fig. 1) which are with few exceptions, porous, single crystals of high-magnesian calcite. Despite their single crystal nature, fracture surfaces do not exhibit the near-perfect {10.4} cleavage characteristic of inorganic calcite. This paradoxical mix of biogenic and inorganic features has prompted much recent work on echinoderm skeletal crystallography. Furthermore, fossil echinoderm hard parts comprise a volumetrically significant portion of some marine limestones sequences. The ultrastructural and microchemical characterization of modern skeletal material should lend insight into: 1). The nature of the biogenic processes involved, for example, the relationship of Mg heterogeneity to morphological and structural features in modern echinoderm material, and 2). The nature of the diagenetic changes undergone by their ancient, fossilized counterparts. In this study, high resolution TEM (HRTEM), high voltage TEM (HVTEM), and STEM microanalysis are used to characterize tha ultrastructural and microchemical composition of skeletal elements of the modern crinoid Neocrinus blakei.

Ultrastructural identification of three types of sensory setae on copepod antennae

1995 ◽  
Vol 53 ◽  
pp. 956-957
Author(s):  
T. M. Weatherby ◽  
P.H. Lenz
Keyword(s):  
Phase Locking ◽  
Membrane Surface ◽  
Reaction Times ◽  
High Sensitivity ◽  
Structural Features ◽  
Calanoid Copepods ◽  
Marine Food Webs ◽  
Dendritic Membrane ◽  
Ultrastructural Characterization

Crustaceans, as well as other arthropods, are covered with sensory setae and hairs, including mechanoand chemosensory sensillae with a ciliary origin. Calanoid copepods are small planktonic crustaceans forming a major link in marine food webs. In conjunction with behavioral and physiological studies of the antennae of calanoids, we undertook the ultrastructural characterization of sensory setae on the antennae of Pleuromamma xiphias.Distal mechanoreceptive setae exhibit exceptional behavioral and physiological performance characteristics: high sensitivity (<10 nm displacements), fast reaction times (<1 msec latency) and phase locking to high frequencies (1-2 kHz). Unusual structural features of the mechanoreceptors are likely to be related to their physiological sensitivity. These features include a large number (up to 3000) of microtubules in each sensory cell dendrite, arising from or anchored to electron dense rods associated with the ciliary basal body microtubule doublets. The microtubules are arranged in a regular array, with bridges between and within rows. These bundles of microtubules extend far into each mechanoreceptive seta and terminate in a staggered fashion along the dendritic membrane, contacting a large membrane surface area and providing a large potential site of mechanotransduction.

Quantitative nano-characterization of heterogeneous catalysts

1995 ◽  
Vol 53 ◽  
pp. 398-399
Author(s):  
P.A. Crozier ◽  
M. Pan
Keyword(s):  
Heterogeneous Catalysts ◽  
Low Dose ◽  
Imaging Techniques ◽  
Structural Features ◽  
Catalyst Characterization ◽  
New Developments ◽  
Double Phase ◽  
Phase Systems ◽  
Dose Imaging

Heterogeneous catalysts can be of varying complexity ranging from single or double phase systems to complicated mixtures of metals and oxides with additives to help promote chemical reactions, extend the life of the catalysts, prevent poisoning etc. Although catalysis occurs on the surface of most systems, detailed descriptions of the microstructure and chemistry of catalysts can be helpful for developing an understanding of the mechanism by which a catalyst facilitates a reaction. Recent years have seen continued development and improvement of various TEM, STEM and AEM techniques for yielding information on the structure and chemistry of catalysts on the nanometer scale. Here we review some quantitative approaches to catalyst characterization that have resulted from new developments in instrumentation.HREM has been used to examine structural features of catalysts often by employing profile imaging techniques to study atomic details on the surface. Digital recording techniques employing slow-scan CCD cameras have facilitated the use of low-dose imaging in zeolite structure analysis and electron crystallography. Fig. la shows a low-dose image from SSZ-33 zeolite revealing the presence of a stacking fault.

Is the Acidic pH of the External Auditory Canal Playing a Significant Role in the Treatment of Acute Otitis Externa?

2018 ◽  
Vol 69 (8) ◽  
pp. 2304-2305
Author(s):  
Oana Ruxandra Iana ◽  
Dragos Cristian Stefanescu ◽  
Viorel Zainea ◽  
Razvan Hainarosie
Keyword(s):  
External Auditory Canal ◽  
Otitis Externa ◽  
Proton Pumps ◽  
Acidic Ph ◽  
External Ear ◽  
Ph Values ◽  
The World ◽  
Subcutaneous Tissues ◽  
Low Levels ◽  
Value Changes

Variable pH values for skin have been reported in the literature, all within the acidic range, varying from 4.0 up to 7. 0. The origin of the acidic pH remains conjectural, and several factors have been incriminated with this role, such as eccrine and sebaceous secretions as well as proton pumps. Keeping low levels of pH prevents microbial dispersal as well as multiplication. The skin in the external auditory canal is also covered with this acidic mantle with antimicrobial value. Changes of pH in the external ear can lead to acute otitis externa. This condition is defined by the inflammation and infection of the cutaneous and subcutaneous tissues of the external auditory canal. 10% of the world�s population may suffer from acute otitis externa at least once in their lifetime. This paper aims to consolidate the relevance of an acidic pH in the healthy external ear and its relation to the pathogenesis and treatment of otitis externa through a prospective and interventional clinical study on 80 patients who presented to the outpatient department at Prof. Dr D. Hociota ENT Institute in Buch

Targeting IDH Mutations in AML: Wielding the Double-edged Sword of Differentiation

2020 ◽  
Vol 20 (7) ◽  
pp. 490-500 ◽  
Author(s):  
Justin S. Becker ◽  
Amir T. Fathi
Keyword(s):  
Genome Structure ◽  
Cellular Metabolism ◽  
Standard Of Care ◽  
Competitive Inhibitor ◽  
Driver Mutations ◽  
New Class ◽  
Regulatory Enzymes ◽  
Idh Mutations ◽  
Genomic Characterization

The genomic characterization of acute myeloid leukemia (AML) by DNA sequencing has illuminated subclasses of the disease, with distinct driver mutations, that might be responsive to targeted therapies. Approximately 15-23% of AML genomes harbor mutations in one of two isoforms of isocitrate dehydrogenase (IDH1 or IDH2). These enzymes are constitutive mediators of basic cellular metabolism, but their mutated forms in cancer synthesize an abnormal metabolite, 2- hydroxyglutarate, that in turn acts as a competitive inhibitor of multiple gene regulatory enzymes. As a result, leukemic IDH mutations cause changes in genome structure and gene activity, culminating in an arrest of normal myeloid differentiation. These discoveries have motivated the development of a new class of selective small molecules with the ability to inhibit the mutant IDH enzymes while sparing normal cellular metabolism. These agents have shown promising anti-leukemic activity in animal models and early clinical trials, and are now entering Phase 3 study. This review will focus on the growing preclinical and clinical data evaluating IDH inhibitors for the treatment of IDH-mutated AML. These data suggest that inducing cellular differentiation is central to the mechanism of clinical efficacy for IDH inhibitors, while also mediating toxicity for patients who experience IDH Differentiation Syndrome. Ongoing trials are studying the efficacy of IDH inhibitors in combination with other AML therapies, both to evaluate potential synergistic combinations as well as to identify the appropriate place for IDH inhibitors within existing standard-of-care regimens.

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