scholarly journals An automatic apparatus for the study of enzyme kinetics

1969 ◽  
Vol 115 (3) ◽  
pp. 511-515 ◽  
Author(s):  
J. A. Illingworth ◽  
K F Tipton
Keyword(s):  
Reaction Times ◽  
Flow Cell ◽  
Reaction Coil ◽  
Automatic Apparatus ◽  
Precise Control ◽  
Fixed Proportion ◽  
Substrate Saturation ◽  
Flow Apparatus ◽  
Variable Substrate ◽  
Linear Concentration

A continuous-flow apparatus is described for automatically plotting substrate saturation curves, and is suitable for use with a variety of enzymes. A linear concentration gradient of the variable substrate is combined with a fixed proportion of the other substrates and the enzyme, and after passing through a reaction coil the product concentrations are measured spectrophotometrically. Use of a 4cm. flow cell and modified spectrophotometer permits accurate measurement of NADH concentration in the region of 0·1μm. Precise control over reaction times and substrate concentration is achieved by using power-driven syringes with an integral mixer. Specimen results are given for yeast alcohol dehydrogenase.

Dynamic Aspects of Phonatory Control in Spasmodic Dysphonia

1987 ◽  
Vol 30 (2) ◽  
pp. 197-206 ◽  
Author(s):  
Christy L. Ludlow ◽  
Nadine P. Connor
Keyword(s):  
Vocal Fold ◽  
Reaction Times ◽  
Movement Control ◽  
Reaction Time Task ◽  
Spasmodic Dysphonia ◽  
Maximum Phonation Time ◽  
Precise Control ◽  
Time Frequency ◽  
Intensity Control ◽  
Normal Controls

To understand the voluntary laryngeal movement disorder in spasmodic dysphonia (SD), SD patients were compared with normal controls on speech tasks with different laryngeal motor-control demands. Nine patients with idiopathic chronic SD and no other speech, otolaryngologic, neurologic, or psychiatric disorders were compared with 15 control subjects who were free of such disorders. Speech production tasks required different degrees of dynamic and precise control of vocal fold movement. Phonatory off times were increased in the SD patients, while maximum phonation time, phonatory on time, frequency and intensity control, and reaction times for CV syllables were not affected. On a reaction-time task, the onset of laryngeal movement was not delayed in the SD patients, however, the time between the onset of laryngeal movement and phonatory onset was significantly increased in the SD patients in comparison with the controls. Therefore, SD patients had no difficulty with the onset of laryngeal movement but were slow to achieve phonation, indicating a movement-control disorder affecting vocal fold adduction for phonation onset.

scholarly journals Recent Advances in Continuous-Flow Reactions Using Metal-Free Homogeneous Catalysts

Catalysts ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1321
Author(s):  
Naoto Sugisawa ◽  
Hiroyuki Nakamura ◽  
Shinichiro Fuse
Keyword(s):  
Continuous Flow ◽  
Low Cost ◽  
Reaction Times ◽  
Toxic Metal ◽  
Homogeneous Catalysts ◽  
Precise Control ◽  
Metal Free ◽  
Acidic Catalysts ◽  
Ready Availability ◽  
Low Toxicity

Developments that result in high-yielding, low-cost, safe, scalable, and less-wasteful processes are the most important goals in synthetic organic chemistry. Continuous-flow reactions have garnered much attention due to many advantages over conventional batch reactions that include precise control of short reaction times and temperatures, low risk in handling dangerous compounds, and ease in scaling up synthesis. Combinations of continuous-flow reactions with homogeneous, metal-free catalysts further enhances advantages that include low-cost and ready availability, low toxicity, higher stability in air and water, and increased synthetic efficiency due to the avoidance of the time-consuming removal of toxic metal traces. This review summarizes recently reported continuous-flow reactions using metal-free homogeneous catalysts and classifies them either as acidic catalysts, basic catalysts, or miscellaneous catalysts. In addition, we compare the results between continuous-flow conditions and conventional batch conditions to reveal the advantages of using flow reactions with metal-free homogeneous catalysts.

Kinetics of the direct chlorination of carbon

1970 ◽  
Vol 23 (4) ◽  
pp. 725 ◽  
Author(s):  
JD Blackwood ◽  
BD Cullis
Keyword(s):  
High Temperature ◽  
Carbon Tetrachloride ◽  
Partial Pressure ◽  
Reaction Times ◽  
Not Given ◽  
Kcal Mole ◽  
Predominant Species ◽  
Flow Apparatus ◽  
Wood Char ◽  
Kinetics Of

Carbon, in the form of a wood char activated by treatment with air and chlorine, has been chlorinated directly at temperatures between 600� and 800� and at chlorine pressures between 3.5 and 20 atm in a flow apparatus to produce carbon tetrachloride as sole reaction product. The rate of formation R of carbon tetrachloride can be expressed by the equation R = ilpa where il is the rate constant for the chemisorption of chlorine on carbon and pa is the partial pressure of chlorine. The rate is also dependent on the nature of the carbon, high temperature carbons being less reactive. The energy of activation for the process is 25 kcal mole-1. When carbon tetrachloride is decomposed in a carbon bed, tetrachloroethylene, hexachloroethane, chlorine, and carbon are formed as products, the predominant species depending on the conditions. This indicated that the overall reaction is not given by the simple equation C + 2Cl2 + CCl4 (I) and, on prolonged reaction times, yields of carbon tetrachloride well below the amount expected at equilibrium for this reaction confirm the finding. pa denotes the partial pressure of Cl2, pb that of CCl4, pc that of C2C14, and pa that of CzCl6.The subscript numerals to i and j refer to the equation numbers in the text.

scholarly journals Steady State and Dynamic Response of Voltage-Operated Membrane Gates

Membranes ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 34
Author(s):  
David Nicolas Østedgaard-Munck ◽  
Jacopo Catalano ◽  
Anders Bentien
Keyword(s):  
Steady State ◽  
Dynamic Response ◽  
Flow Cell ◽  
Low Energy ◽  
Energy Requirements ◽  
Carbon Paper ◽  
Pump Operation ◽  
Precise Control ◽  
Voltage Gated ◽  
Electrochemical Flow Cell

An electrochemical flow cell with Nafion 212, aqueous LiI/I 2 redox solution, and carbon paper electrode was operated as an electro-osmotic gate based on the Electrokinetic Energy Conversion (EKEC) principle. The gate was operated in different modes. (i) In normal DC pump operation it is shown to follow the predictions from the phenomenological transport equations. (ii) Furthermore, it was also demonstrated to operate as a normally open, voltage-gated valve for microfluidic purposes. For both pump and valve operations low energy requirements (mW range) were estimated for precise control of small flows ( μ L range). (iii) Finally, the dynamic response of the pump was investigated by using alternating currents at a range of different frequencies.

Regulation of pyruvate kinases from Fusarium oxysporum

1977 ◽  
Vol 23 (10) ◽  
pp. 1346-1359 ◽  
Author(s):  
M. W. Zink
Keyword(s):  
Citric Acid ◽  
Fusarium Oxysporum ◽  
Adenosine Diphosphate ◽  
Major Type ◽  
Potassium Ions ◽  
Saturation Curve ◽  
Pyruvate Kinase Activity ◽  
Substrate Saturation ◽  
Pyruvate Kinases ◽  
Variable Substrate

Two types of pyruvate kinases were found in Fusarium oxysporum. One type (inducible) was present mainly during the early stages of growth on glucose or sucrose and displayed Michaelis–Menten kinetics with respect to phosphoenolpyruvate and adenosine diphosphate. The major type (constitutive) was present under all conditions of growth and displayed in the absence of potassium ions, a sigmoidal substrate saturation curve when phosphoenolpyruvate was used as the variable substrate. In the presence of potassium ions the saturation curve for phosphoenolpyruvate exhibits a plateau at half-maximal velocity.The effects of various metabolites on the activity of the inducible and constitutive kinases were also studied. Fructose-1,6-diphosphate, cyclic AMP, acetyl Co A, tryptophan, and phenylalanine had no effect on the activity of the enzymes. Citrate was a potent inhibitor of the constitutive pyruvate kinase activity and increased the sigmoidicity of the saturation curve for phosphoenolpyruvic acid. In the presence of K+, the bimodal plot observed in the absence of citrate gradually changed to a hyperbolic shape as the concentration of citric acid was increased. In the presence of K+ and ADP as the variable substrate citric acid converted the hyperbolic plot to a sigmoidal one. Citrate had no effect on the inducible enzyme.

SUB-SECOND CALCIUM DYNAMICS IN ADP AND THROMBIN-STIMULATED PLATELETS; ASSESSED BY A C0NTINU0US-EL0W APPROACH

1987 ◽  
Author(s):  
A R L Gear ◽  
G D Jones
Keyword(s):  
Protein Phosphorylation ◽  
Shape Change ◽  
Reaction Times ◽  
Human Platelets ◽  
Free Calcium ◽  
Calcium Dynamics ◽  
On Line ◽  
Micro Flow ◽  
Flow Apparatus ◽  
Emission Changes

There is now evidence that many platelet reactions begin within 1 sec of platelet stimulation. These include "shape change," aggregation and biochemical events such as protein phosphorylation. Our laboratory has devised quenched-flow approaches for following such early events (J Lab Clin Med 100, 866, 1982) and we have extended these to fluorimetric analyses of rapid calcium changes. A micro, flow-through cell, with a sensing volume of 0.1 μ1, is placed on line from the quenched-flow apparatus. Indo-1 loaded, human platelets are pumped through the system and reaction times from 0.25 sec can be followed. Ratioing emission changes at 400 and 480 nm, after excitation at 355 nm, provides an index of free calcium. ADP (10 μM) induced a rapid increase in Ca++ to about 1 μM by 1.5 sec, beginning near 0.3 sec. This was faster and greater than the first increase caused by thrombin (10U/ml). However, thrombin induced a second (> 5s) and larger increase in free platelet calcium. Control experiments where the Indo-1 loaded platelets were simply pumped through the 0.3 mm ID reaction tubing, revealed a slight increase above resting calcium values, indicating some shear-induced activation. The use of the continuous-flow fluorescent cell coupled to the quenched-flow apparatus enables following calcium dynamics under Theological conditions very close to those iui vivo.Correlations with other early events, such as protein phosphorylation, become possible. Supported by NIH HL-27014.

A Novel Reconstitution Method for Inducing the Formation of Regular 2-Dimensional Arrays of Membrane Proteins and Lipids

1988 ◽  
Vol 46 ◽  
pp. 152-153 ◽  
Author(s):  
A. Engel ◽  
A. Holzenburg ◽  
K. Stauffer ◽  
J. Rosenbusch ◽  
U. Aebi
Keyword(s):  
Membrane Proteins ◽  
Flow Rate ◽  
Lipid Membranes ◽  
Functional Characterization ◽  
Dimensional Structure ◽  
Electron Crystallography ◽  
Peltier Element ◽  
Protein Ratio ◽  
Precise Control ◽  
3 Dimensional

Reconstitution of solubilized and purified membrane proteins in the presence of phospholipids into vesicles allows their functions to be studied by simple bulk measurements (e.g. diffusion of differently sized solutes) or by conductance measurements after transformation into planar membranes. On the other hand, reconstitution into regular protein-lipid arrays, usually forming at a specific lipid-to-protein ratio, provides the basis for determining the 3-dimensional structure of membrane proteins employing the tools of electron crystallography.To refine reconstitution conditions for reproducibly inducing formation of large and highly ordered protein-lipid membranes that are suitable for both electron crystallography and patch clamping experiments aimed at their functional characterization, we built a flow-dialysis device that allows precise control of temperature and flow-rate (Fig. 1). The flow rate is generated by a peristaltic pump and can be adjusted from 1 to 500 ml/h. The dialysis buffer is brought to a preselected temperature during its travel through a meandering path before it enters the dialysis reservoir. A Z-80 based computer controls a Peltier element allowing the temperature profile to be programmed as function of time.

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.

Multiple-fracturing and viewing of the same frozen sample at different depths using a low temperature FESEM

1996 ◽  
Vol 54 ◽  
pp. 820-821
Author(s):  
M.V. Parthasarathy ◽  
C. Daugherty
Keyword(s):  
Temperature Field ◽  
Low Temperature ◽  
Field Emission ◽  
Multiple Fracture ◽  
Precise Control ◽  
Cold Stage ◽  
Different Depths ◽  
Transfer Device

The versatility of Low Temperature Field Emission SEM (LTFESEM) for viewing frozen-hydrated biological specimens, and the high resolutions that can be obtained with such instruments have been well documented. Studies done with LTFESEM have been usually limited to the viewing of small organisms, organs, cells, and organelles, or viewing such specimens after fracturing them.We use a Hitachi 4500 FESEM equipped with a recently developed BAL-TEC SCE 020 cryopreparation/transfer device for our LTFESEM studies. The SCE 020 is similar in design to the older SCU 020 except that instead of having a dedicated stage, the SCE 020 has a detachable cold stage that mounts on to the FESEM stage when needed. Since the SCE 020 has a precisely controlled lock manipulator for transferring the specimen table from the cryopreparation chamber to the cold stage in the FESEM, and also has a motor driven microtome for precise control of specimen fracture, we have explored the feasibility of using the LTFESEM for multiple-fracture studies of the same sample.

Factors Influencing Cognate Performance for Young Multilingual Children's Vocabulary: A Research Synthesis

2020 ◽  
Vol 29 (4) ◽  
pp. 2170-2188
Author(s):  
Lindsey R. Squires ◽  
Sara J. Ohlfest ◽  
Kristen E. Santoro ◽  
Jennifer L. Roberts
Keyword(s):  
Test Validity ◽  
Reaction Times ◽  
Bilingual Children ◽  
Second Grade ◽  
High Quality Research ◽  
Word Level ◽  
Research Questions ◽  
Word Characteristics ◽  
Study Inclusion ◽  
Task Level

Purpose The purpose of this systematic review was to determine evidence of a cognate effect for young multilingual children (ages 3;0–8;11 [years;months], preschool to second grade) in terms of task-level and child-level factors that may influence cognate performance. Cognates are pairs of vocabulary words that share meaning with similar phonology and/or orthography in more than one language, such as rose – rosa (English–Spanish) or carrot – carotte (English–French). Despite the cognate advantage noted with older bilingual children and bilingual adults, there has been no systematic examination of the cognate research in young multilingual children. Method We conducted searches of multiple electronic databases and hand-searched article bibliographies for studies that examined young multilingual children's performance with cognates based on study inclusion criteria aligned to the research questions. Results The review yielded 16 articles. The majority of the studies (12/16, 75%) demonstrated a positive cognate effect for young multilingual children (measured in higher accuracy, faster reaction times, and doublet translation equivalents on cognates as compared to noncognates). However, not all bilingual children demonstrated a cognate effect. Both task-level factors (cognate definition, type of cognate task, word characteristics) and child-level factors (level of bilingualism, age) appear to influence young bilingual children's performance on cognates. Conclusions Contrary to early 1990s research, current researchers suggest that even young multilingual children may demonstrate sensitivity to cognate vocabulary words. Given the limits in study quality, more high-quality research is needed, particularly to address test validity in cognate assessments, to develop appropriate cognate definitions for children, and to refine word-level features. Only one study included a brief instruction prior to assessment, warranting cognate treatment studies as an area of future need. Supplemental Material https://doi.org/10.23641/asha.12753179

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