Tyrosine Biosynthesis in Sorghum bicolor: Characteristics of Prephenate Aminotransferase

1986 ◽  
Vol 41 (1-2) ◽  
pp. 79-86 ◽  
Author(s):  
Daniel L. Siehl ◽  
James A. Connelly ◽  
Eric E. Conn
Keyword(s):  
Reaction Rate ◽  
Deae Cellulose ◽  
Forward Direction ◽  
Reverse Direction ◽  
Aminotransferase Activity ◽  
Forward Reaction ◽  
High Affinity ◽  
Sorghum Plant ◽  
Arogenate Dehydrogenase ◽  
Tyrosine Biosynthesis

Abstract A stable activity which transfers the amino group from glutamate to prephenate was extracted from 4-day old etiolated shoots of sorghum. The activity was retained on DEAE cellulose and eluted as a single peak. Prephenate aminotransferase co-eluted with a very abundant α-ketoglutarate: aspartate aminotransferase, but heating at 70 °C resulted in loss of α-ketoglutarate: aspar­tate activity with nearly full retention of prephenate: glutamate aminotransferase activity. The heated enzyme displayed high affinity and specificity for prephenate. Among 7 donors tested, only glutamate, and aspartate at less than 20% the rate with glutamate, supported prephenate aminotransferase activity. In the reverse direction, a reaction rate comparable to that in the forward direction was unchanged as the concentration of α-ketoglutarate was reduced from 1.0 to 0.09 mᴍ. The apparent Km for arogenate was 0.8 mᴍ. The forward reaction was unaffected by the inclusion of tyrosine, phenylalanine or tryptophan. Together with the discovery of arogenate dehydrogenase in sorghum [3], these data indicate that, in the sorghum plant, tyrosine derives from prephenate by transamination and aromatization. rather than the reverse sequence.

Phenylalanine and Tyrosine Biosynthesis in Sporeforming Members of the Order Actinomycetales

1987 ◽  
Vol 42 (4) ◽  
pp. 387-393 ◽  
Author(s):  
Hilda-K. Hund ◽  
Brigitte Keller ◽  
Franz Lingens
Keyword(s):  
Anion Exchange ◽  
Deae Cellulose ◽  
Anion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Chorismate Mutase ◽  
Biosynthetic Enzymes ◽  
Prephenate Dehydratase ◽  
Prephenate Dehydrogenase ◽  
Arogenate Dehydrogenase ◽  
Tyrosine Biosynthesis

Abstract The enzymes of the terminal steps of phenylalanine and tyrosine biosynthesis, chorismate mutase, prephenate dehydratase, arogenate dehydratase, prephenate dehydrogenase and aroge­ nate dehydrogenase were studied in 13 sporeforming members of the order Actinomycetales. In these organisms tyrosine is synthesized exclusively via arogenate, phenylalanine, however, via phenylpyruvate. The regulation pattern of the corresponding enzymes was determined: No feed­ back inhibition of arogenate dehydrogenase by L-phenylalanine and ʟ-tyrosine was observed. Chorismate mutase was found to be inhibited in all organisms by ʟ-tyrosine and in most organisms by ʟ-tryptophan. ʟ-Phenylalanine was shown to inhibit prephenate dehydratase in the majority of bacteria tested and ʟ-tyrosine activated this enzyme in most cases. The elution profiles for the phenylalanine and tyrosine biosynthetic enzymes were studied in three members of the order Actinomycetales by anion exchange chromatography on DEAE-cellulose.

Tyrosine Biosynthesis in Sorghum bicolor: Isolation and Regulatory Properties of Arogenate Dehydrogenase

1986 ◽  
Vol 41 (1-2) ◽  
pp. 69-78 ◽  
Author(s):  
James A. Connelly ◽  
Eric E. Conn
Keyword(s):  
Amino Acid ◽  
Deae Cellulose ◽  
Shikimate Pathway ◽  
Oxidative Decarboxylation ◽  
Strong Inhibition ◽  
High Recovery ◽  
Prephenate Dehydrogenase ◽  
Arogenate Dehydrogenase ◽  
Tyrosine Biosynthesis ◽  
Regulatory Properties

Abstract The conversion of prephenic acid to tyrosine can occur by two different routes: (a) oxidative decarboxylation (prephenate dehydrogenase) followed by transamination (aromatic aminotrans­ ferase); (b) transamination of prephenate forming the non-aromatic amino acid arogenic acid (prephenate am inotransferase) followed by oxidative decarboxylation (arogenate dehydrogenase). High activity of arogenate dehydrogenase was found in extracts of etiolated sorghum seedlings, while no evidence of prephenate dehydrogenase was observed. Arogenate dehydrogenase from sorghum eluted, with high recovery of activity (93%), as a single peak on DEAE-cellulose chromatography. The enzyme was strongly inhibited by tyrosine but was unaffected by phenylala­nine, prephenate, or tryptophan. Kinetic analysis showed that tyrosine inhibition was competitive with arogenate and that the Ki for tyrosine (61 μm) was much smaller than the Km for arogenate (350 μm). The properties of arogenate dehydrogenase indicate that this enzyme is important in the regula­tion of tyrosine biosynthesis in sorghum. Strong inhibition of the enzyme by tyrosine may indicate that arogenate is a branch point in the shikimate pathway in plants and therefore arogenate may be a precursor to phenylalanine and the numerous phenylpropanoid secondary metabolites deriv­ed from phenylalanine.

scholarly journals Brain-wide mapping of water flow perception in zebrafish

2020 ◽  
Author(s):  
Gilles Vanwalleghem ◽  
Kevin Schuster ◽  
Michael A. Taylor ◽  
Itia A. Favre-Bulle ◽  
Ethan K. Scott
Keyword(s):  
Water Flow ◽  
Lateral Line ◽  
Reverse Flow ◽  
Forward Direction ◽  
Brain Regions ◽  
Reverse Direction ◽  
Departure Point ◽  
Forward Flow ◽  
Larval Zebrafish ◽  
The Brain

AbstractInformation about water flow, detected by lateral line organs, is critical to the behavior and survival of fish and amphibians. While certain specific aspects of water flow processing have been revealed through electrophysiology, we lack a comprehensive description of the neurons that respond to water flow and the network that they form. Here, we use brain-wide calcium imaging in combination with microfluidic stimulation to map out, at cellular resolution, all neurons involved in perceiving and processing water flow information in larval zebrafish. We find a diverse array of neurons responding to forward flow, reverse flow, or both. Early in this pathway, in the lateral line ganglia, these are almost exclusively neurons responding to the simple presence of forward or reverse flow, but later processing includes neurons responding specifically to flow onset, representing the accumulated volume of flow during a stimulus, or encoding the speed of the flow. The neurons reporting on these more nuanced details are located across numerous brain regions, including some not previously implicated in water flow processing. A graph theory-based analysis of the brain-wide water flow network shows that a majority of this processing is dedicated to forward flow detection, and this is reinforced by our finding that details like flow velocity and the total volume of accumulated flow are only encoded for the simulated forward direction. The results represent the first brain-wide description of processing for this important modality, and provide a departure point for more detailed studies of the flow of information through this network.Significance statementIn aquatic animals, the lateral line is important for detecting water flow stimuli, but the brain networks that interpret this information remain mysterious. Here, we have imaged the activity of individual neurons across the entire brains of larval zebrafish, revealing all response types and their brain locations as water flow processing occurs. We find some neurons that respond to the simple presence of water flow, and others that are attuned to the flow’s direction, speed, duration, or the accumulated volume of water that has passed during the stimulus. With this information, we modeled the underlying network, describing a system that is nuanced in its processing of water flow simulating forward motion but rudimentary in processing flow in the reverse direction.

scholarly journals Endothelial cell-derived heparan sulfate binds basic fibroblast growth factor and protects it from proteolytic degradation.

1988 ◽  
Vol 107 (2) ◽  
pp. 743-751 ◽  
Author(s):  
O Saksela ◽  
D Moscatelli ◽  
A Sommer ◽  
D B Rifkin
Keyword(s):  
Growth Factor ◽  
Heparan Sulfate ◽  
Fibroblast Growth Factor ◽  
Basic Fibroblast Growth Factor ◽  
Deae Cellulose ◽  
Proteolytic Degradation ◽  
Fibroblast Growth ◽  
Intact Cells ◽  
High Affinity ◽  
Cell Extracts

Cultured bovine capillary endothelial (BCE) cells were found to synthesize and secrete high molecular mass heparan sulfate proteoglycans and glycosaminoglycans, which bound basic fibroblast growth factor (bFGF). The secreted heparan sulfate molecules were purified by DEAE cellulose chromatography, followed by Sepharose 4B chromatography and affinity chromatography on immobilized bFGF. Most of the heparinase-sensitive sulfated molecules secreted into the medium by BCE cells bound to immobilized bFGF at low salt concentrations. However, elution from bFGF with increasing salt concentrations demonstrated varying affinities for bFGF among the secreted heparan sulfate molecules, with part of the heparan sulfate requiring NaCl concentrations between 1.0 and 1.5 M for elution. Cell extracts prepared from BCE cells also contained a bFGF-binding heparan sulfate proteoglycan, which could be released from the intact cells by a short proteinase treatment. The purified bFGF-binding heparan sulfate competed with 125I-bFGF for binding to low-affinity binding sites but not to high-affinity sites on the cells. Heparan sulfate did not interfere with bFGF stimulation of plasminogen activator activity in BCE cells in agreement with its lack of effect on binding of 125I-bFGF to high-affinity sites. Soluble bFGF was readily degraded by plasmin, whereas bFGF bound to heparan sulfate was protected from proteolytic degradation. Treatment of the heparan sulfate with heparinase before addition of plasmin abolished the protection and resulted in degradation of bFGF by the added proteinase. The results suggest that heparan sulfate released either directly by cells or through proteolytic degradation of their extracellular milieu may act as carrier for bFGF and facilitate the diffusion of locally produced growth factor by competing with its binding to surrounding matrix structures. Simultaneously, the secreted heparan sulfate glycosaminoglycans protect the growth factor from proteolytic degradation by extracellular proteinases, which are abundant at sites of neovascularization or cell invasion.

UPTAKE AND BINDING OF GLUCOCORTICOIDS IN FISH TISSUES

1978 ◽  
Vol 78 (3) ◽  
pp. 407-416 ◽  
Author(s):  
JACQUELINE PORTHÉ-NIBELLE ◽  
BRAHIM LAHLOU
Keyword(s):  
Binding Sites ◽  
Large Range ◽  
Deae Cellulose ◽  
High Rate ◽  
Intravascular Injection ◽  
Fish Tissues ◽  
High Affinity ◽  
Nuclear Membranes ◽  
Free Steroid ◽  
Fold Excess

Cytosols prepared from the liver and various tissues of goldfish (intact or hypophysectomized) and trout (intact) were incubated at 2 °C in the presence of tritiated cortisol or dexamethasone (3 × 10−9 to 3 × 10−6 mol/l) with or without a 1000-fold excess of unlabelled steroid. In contrast to mammals, the specifically bound component represented a very low fraction of the total bound steroid retained on DEAE cellulose filters and did not show saturation over a large range of concentrations. The subcellular distribution of [3H]dexamethasone was studied in trout liver after intravascular injection of the labelled steroid with and without an excess of unlabelled steroid. The amount of protein-bound steroid in the cytosol again corresponded to a small (4%) proportion of the free steroid. The large reduction in the uptake of tritiated dexamethasone, which was induced in both the cytosol and nuclei by competing unlabelled dexamethasone, was interpreted as evidence for mediated entry across cellular and nuclear membranes. These results indicate that high-affinity binding sites are absent, or present only in very small numbers in cytosol from teleost tissues. The entry of glucocorticoids into the nucleus may not require the hormone to be bound to high-affinity cytosolic receptors unless the binding, though quantitatively small, displays a high rate of turnover.

RADIATED ACOUSTIC PRESSURE FROM A MOVING, NONUNIFORMLY VIBRATING CYLINDER WITH TWO SPHERICAL ENDCAPS

1994 ◽  
Vol 02 (01) ◽  
pp. 71-82 ◽  
Author(s):  
ZHAOXI WANG ◽  
SEAN F. WU
Keyword(s):  
Near Field ◽  
Translational Motion ◽  
Normal Component ◽  
Forward Direction ◽  
Numerical Results ◽  
Surface Velocity ◽  
Reverse Direction ◽  
Far Field ◽  
Field Source ◽  
Sound Diffraction

This paper presents numerical results of radiated acoustic pressures from a moving, nonuniformly vibrating cylinder with two spherical endcaps, based on an extended Kirchhoff integral formulation. Specifically, we consider cases in which the normal component of the surface velocity is nonzero on a portion of the surface, and zero elsewhere. Numerical results demonstrate that the radiation patterns depend critically on the frequency and source dimensions. For a noncompact source, the strongest radiation may not necessarily stem from a vibrating surface, but rather from a nonvibrating surface due to the effect of sound diffraction. The more noncompact the source is, the larger the number of side lobes in the near field and the more concentrated these side lobes will be. In the far field, however, the side lobes become smeared and less distinguishable. In other words, the effect of sound diffraction is greatly reduced in the far field. Source translational motion induces sound radiation in the perpendicular direction and enhances the radiated acoustic field in general. Enhancement in the forward direction is much greater than in the reverse direction.

scholarly journals Inhibition of the soluble adenosine triphosphatase from mitochondria by adenylyl imidodiphosphate

1974 ◽  
Vol 143 (3) ◽  
pp. 745-749 ◽  
Author(s):  
Roger D. Philo ◽  
Michael J. Selwyn
Keyword(s):  
Atpase Activity ◽  
Rate Constants ◽  
Binding Sites ◽  
Adenosine Triphosphatase ◽  
Reaction Rate ◽  
Dissociation Reaction ◽  
Reaction Rate Constants ◽  
High Affinity ◽  
Number Of Binding Sites ◽  
Inosine Triphosphatase

1. Adenylyl imidodiphosphate is an inhibitor with high affinity for the soluble ATPase (adenosine triphosphatase) from mitochondria. 2. The reaction of the inhibitor with the ATPase is slow and estimates for the association and dissociation reaction rate constants are given. 3. The number of binding sites for the inhibitor appears to be doubled in the presence of 2,4-dinitrophenol. 4. Adenylyl imidodiphosphate is less effective as an inhibitor of the ATPase activity of this enzyme than of the inosine triphosphatase activity. It is also less effective on the ATPase of frozen-thawed or intact mitochondria and did not inhibit ADP-stimulated respiration by intact mitochondria.

AN EXPERIMENTAL STUDY ON THE TRANSIENT TEMPERATURE TEST OF THE PLANETARY GEAR REDUCER OF THE EPBM

2011 ◽  
Vol 10 (01) ◽  
pp. 37-43 ◽  
Author(s):  
LIFENG CHEN ◽  
XIAOLING WU ◽  
DATONG QIN ◽  
ZEJUN WEN
Keyword(s):  
Temperature Rise ◽  
Planetary Gear ◽  
Forward Direction ◽  
Test System ◽  
Gear Train ◽  
Reverse Direction ◽  
Transient Temperature ◽  
Pressure Balance ◽  
Planetary Gear Train ◽  
Temperature Test

A temperature test apparatus has been designed to measure the temperature rise of the planetary gear train. The experimental platform integrated the temperature test system, siemens operating system and industrial personal computer (IPC). The temperatures of various locations have been investigated under rated condition and the oil temperature-rise time under different speed was estimated. The experimental results indicated that the temperatures of the super-speed planetary gear train (PGT) of the earth pressure balance shield machine (EPBM) rise quickly than the low-speed PGT and the speed has significant influence on the temperature of the PGT. Through comparison the oil temperatures under reverse direction and forward direction, the direction of the motor has little influence on the temperature of the PGT.

scholarly journals pH-induced bistable dynamic behaviour in the reaction catalysed by glucose-6-phosphate dehydrogenase and conformational hysteresis of the enzyme

1989 ◽  
Vol 262 (3) ◽  
pp. 795-800 ◽  
Author(s):  
M A Aon ◽  
S Cortassa ◽  
J F Hervagault ◽  
D Thomas
Keyword(s):  
Dynamic Behaviour ◽  
Forward Direction ◽  
Memory Device ◽  
Reverse Direction ◽  
Protein Fluorescence ◽  
Ph Change ◽  
Before And After ◽  
Continuously Stirred Tank Reactor ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Intrinsic Protein Fluorescence

1. Bistable (multiple stationary states) dynamic behaviour in the activity of glucose-6-phosphate dehydrogenase that was subjected to successive pH change was demonstrated in an open continuously stirred tank reactor. Although the enzyme under study did not exhibit an autocatalytic effect and was homogeneously distributed, bistability was shown to occur. 2. The successive pH changes of the enzyme solution corresponded to a pH transition (8.3 in equilibrium 2), i.e. an acidification (forward direction) and an alkalinization (reverse direction). By use of intrinsic protein fluorescence methods, a glucose-6-phosphate dehydrogenase conformational hysteresis was shown to exist concomitant with the pH transition before and after enzyme injection into the reactor. 3. The results obtained suggest that the enzyme behaves, conformationally, as a memory device that stores information about its pH history (i.e. the enzyme records information in its structure about the environment to which it was previously exposed) and transduces it in a non-linear dynamic fashion, producing the bistable behaviour observed in the open reactor.

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