scholarly journals Fungal Cellulases VI. SUBSTRATE AND INHIBITOR SPECIFICITY OF THE fl-GLUCOSIDASE OF ST ACHYBOTRYS ATRA

1955 ◽  
Vol 8 (4) ◽  
pp. 577 ◽  
Author(s):  
MA Jermyn
Keyword(s):  
Marked Decrease ◽  
Inhibitor Specificity ◽  
Hydrolysis Of

A large number of compounds with glycosidic linkages have been tested as substrates for the ,8-glucosidase of Stachybotrys atm. The enzyme appears to be specific for ,8-glucosides and all configurational alterations to the D-glucopyranose ring or substitutions in it lead to non-substrates; phenyl-fl-thioglucoside is a substrate, however. Aryl-,8-glucosides have a higher affinity for the enzyme than alkyl-,8-glucosides and no hydrolysis of cellobiose by the enzyme can be demonstrated. arrha-Substitution in aryl-fl-glucosides leads to a marked decrease in the affinity between enzyme and substrate.

scholarly journals AN ATTEMPT AT PEPTIC SYNTHESIS OF INSULIN

1933 ◽  
Vol 16 (5) ◽  
pp. 741-755 ◽  
Author(s):  
A. M. Fisher ◽  
D. A. Scott
Keyword(s):  
Marked Decrease ◽  
Physiological Activity ◽  
Alcoholic Solution ◽  
Concentrated Solutions ◽  
Crystalline Insulin ◽  
Egg Albumin ◽  
Repeated Freezing ◽  
Hydrolysis Of

1. Synthesis of plastein from the products of peptic hydrolysis of small quantities of egg albumin can be demonstrated with amorphous or crystalline pepsin. 2. Synthesis of plastein from the products of peptic hydrolysis of amorphous or crystalline insulin can be demonstrated with amorphous or crystalline pepsin. 3. The plastein synthesised by pepsin from the products of peptic hydrolysis of insulin is physiologically inactive. 4. The plastein formed in the insulin experiments could not be crystallised by the methods used for the crystallisation of insulin. 5. The physiological activity of insulin is not destroyed by repeated freezing (at about –50°C.) and melting of an aqueous or an alcoholic solution of this hormone. 6. No marked decrease in the physiological activity of insulin after incubation at 37°C. with pepsin at pH 4.0, in dilute or concentrated solutions, was detected.

scholarly journals Importance of the His-298 residue in the catalytic mechanism of the Streptomyces R61 extracellular dd-peptidase

1992 ◽  
Vol 282 (2) ◽  
pp. 495-500 ◽  
Author(s):  
A M Hadonou ◽  
M Jamin ◽  
M Adam ◽  
B Joris ◽  
J Dusart ◽  
...  
Keyword(s):  
Active Site ◽  
Catalytic Mechanism ◽  
Marked Decrease ◽  
Cephalosporin C ◽  
Striking Result ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Substrate Hydrolysis

Among the active-site-serine penicillin-recognizing proteins, the Streptomyces R61 extracellular DD-peptidase is the only one to have a His-Thr-Gly sequence [instead of Lys-Thr(Ser)-Gly] in ‘box’ VII. The His residue was replaced by Gln or Lys. Both mutations induced a marked decrease in the rates of both tripeptide substrate hydrolysis and acylation by benzylpenicillin and cephalosporin C. The rate of hydrolysis of the thioester hippuryl thioglycollate was less affected. The most striking result was the disproportionate loss of transpeptidation properties by both mutants, indicating an important role of His-298 in this reaction. We believe that this result represents the first modification of a DD-peptidase leading to a specific decrease of the transpeptidation-to-hydrolysis ratio.

scholarly journals The kinetic salt effect in monolayer reactions

1948 ◽  
Vol 194 (1039) ◽  
pp. 417-428 ◽  
Keyword(s):  
Marked Decrease ◽  
Ester Group ◽  
Neutral Salt ◽  
Surface Phase ◽  
Equilibrium Equations ◽  
Hydroxyl Ion ◽  
Rate Of Hydrolysis ◽  
Ester Linkage ◽  
Hydrolysis Of ◽  
Phase Activity

The rate of hydrolysis of the ester group in the monocetylsuccinate ion by hydroxyl ion has been studied as a monolayer reaction at various alkali strengths and in the presence of neutral salts. The Donnan equilibrium equations have been employed to calculate the concentration of the hydroxyl ions near the ester linkage, and the hydrolysis constants are found to show a very marked decrease in divergence when referred to the concentration of alkali in the surface, rather than that in the bulk phase. Activity coefficients of the ions in the surface phase have been calculated by the method of linear log plots of Harned, and Brönsted’s theory of specific ion interaction was extended to treat the case of the surface phase in the presence of added neutral salt. The slowing up of the alkaline hydrolysis of a neutral ester of a long-chain acid can also be quantitatively explained assuming the existence of a ‘ surface phase', as can also the potential difference between the surface and the bulk.

scholarly journals Role of residues 104, 164, 166, 238 and 240 in the substrate profile of PER-1 β-lactamase hydrolysing third-generation cephalosporins

1998 ◽  
Vol 330 (3) ◽  
pp. 1443-1449 ◽  
Author(s):  
Anne-Typhaine BOUTHORS ◽  
Nathalie DAGONEAU-BLANCHARD ◽  
Thierry NAAS ◽  
Patrice NORDMANN ◽  
Vincent JARLIER ◽  
...  
Keyword(s):  
Marked Decrease ◽  
Residual Activity ◽  
Catalytic Efficiency ◽  
Site Directed Mutagenesis ◽  
Amino Acid Residues ◽  
Important Residue ◽  
Bond Network ◽  
Hydrolysis Of ◽  
Third Generation Cephalosporins

The class A β-lactamase PER-1, which displays 26% identity with the TEM-type extended-spectrum β-lactamases (ESBLs), catalyses the hydrolysis of oxyimino-β-lactams such as cefotaxime (CTX), ceftazidime (CAZ) and aztreonam (AZT). Molecular modelling was used to identify in PER-1 the amino acid residues corresponding to those found at positions 104, 164, 238 and 240 in the TEM-type ESBLs, which are critical for hydrolysis of oxyimino-β-lactams. The function of these residues in PER-1 was assessed by site-directed mutagenesis. In this enzyme, residue 104 could be either a glutamine, an asparagine or a threonine. The Gln → Gly mutation did not significantly affect the catalytic efficiency, while Asn → Gly and Thr → Glu resulted in a marked decrease in catalytic activity, probably due to the alteration of a hydrogen bond network connecting the putative Asn-104 residue to Asn-132 and Glu-166. Replacement of Ala-164 by Arg in PER-1 resulted in a mutant with no detectable activity, thus suggesting that Ala-164 is important for catalysis and stability of PER-1. Conversely, Ser-238 → Gly and Gly-240 → Glu had little effect on kcat and Km values. Finally, the replacement of the catalytic residue Glu-166 by an alanine resulted in a complete loss of activity for CTX and a marked decrease of kcat for CAZ and AZT. These results suggest that Glu-166 is an important residue in PER-1. However, residues other than Glu-166 could contribute in maintaining residual activity towards oxyimino-β-lactams in the Ala-166 mutant.

Fine Structural Localization of Acyltransferases Involved in Lipid Synthesis in Intestinal Mucosa.

1970 ◽  
Vol 28 ◽  
pp. 54-55
Author(s):  
R. J. Barrnett ◽  
J. A. Higgins
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Lipid Synthesis ◽  
Mucosal Cell ◽  
Structural Localization ◽  
Morphological Studies ◽  
Mucosal Cells ◽  
Initial Appearance ◽  
Sh Group ◽  
Hydrolysis Of ◽  
Intestinal Mucosal Cells

The main products of intestinal hydrolysis of dietary triglycerides are free fatty acids and monoglycerides. These form micelles from which the lipids are absorbed across the mucosal cell brush border. Biochemical studies have indicated that intestinal mucosal cells possess a triglyceride synthesising system, which uses monoglyceride directly as an acylacceptor as well as the system found in other tissues in which alphaglycerophosphate is the acylacceptor. The former pathway is used preferentially for the resynthesis of triglyceride from absorbed lipid, while the latter is used mainly for phospholipid synthesis. Both lipids are incorporated into chylomicrons. Morphological studies have shown that during fat absorption there is an initial appearance of fat droplets within the cisternae of the smooth endoplasmic reticulum and that these subsequently accumulate in the golgi elements from which they are released at the lateral borders of the cell as chylomicrons.We have recently developed several methods for the fine structural localization of acyltransferases dependent on the precipitation, in an electron dense form, of CoA released during the transfer of the acyl group to an acceptor, and have now applied these methods to a study of the fine structural localization of the enzymes involved in chylomicron lipid biosynthesis. These methods are based on the reduction of ferricyanide ions by the free SH group of CoA.

Lattice imaging and pore structure of β ferric oxyhydroxide

1978 ◽  
Vol 36 (1) ◽  
pp. 264-265
Author(s):  
T. Baird ◽  
J.R. Fryer ◽  
S.T. Galbraith
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Bulk Material ◽  
Model Structure ◽  
Bulk Crystals ◽  
Lattice Imaging ◽  
Thin Sections ◽  
Ferric Oxyhydroxide ◽  
Resolution Electron ◽  
Hydrolysis Of

Introduction Previously we had suggested (l) that the striations observed in the pod shaped crystals of β FeOOH were an artefact of imaging in the electron microscope. Contrary to this adsorption measurements on bulk material had indicated the presence of some porosity and Gallagher (2) had proposed a model structure - based on the hollandite structure - showing the hollandite rods forming the sides of 30Å pores running the length of the crystal. Low resolution electron microscopy by Watson (3) on sectioned crystals embedded in methylmethacrylate had tended to support the existence of such pores.We have applied modern high resolution techniques to the bulk crystals and thin sections of them without confirming these earlier postulatesExperimental β FeOOH was prepared by room temperature hydrolysis of 0.01M solutions of FeCl3.6H2O, The precipitate was washed, dried in air, and embedded in Scandiplast resin. The sections were out on an LKB III Ultramicrotome to a thickness of about 500Å.

Elucidating cyclic AMP signaling in subcellular domains with optogenetic tools and fluorescent biosensors

2019 ◽  
Vol 47 (6) ◽  
pp. 1733-1747 ◽  
Author(s):  
Christina Klausen ◽  
Fabian Kaiser ◽  
Birthe Stüven ◽  
Jan N. Hansen ◽  
Dagmar Wachten
Keyword(s):  
Cyclic Amp ◽  
Adenosine Monophosphate ◽  
Adenylyl Cyclases ◽  
Temporal Precision ◽  
Fluorescent Biosensors ◽  
Subcellular Domains ◽  
Spatio Temporal ◽  
Hydrolysis Of ◽  
Shed Light ◽  
Cyclic Amp Signaling

The second messenger 3′,5′-cyclic nucleoside adenosine monophosphate (cAMP) plays a key role in signal transduction across prokaryotes and eukaryotes. Cyclic AMP signaling is compartmentalized into microdomains to fulfil specific functions. To define the function of cAMP within these microdomains, signaling needs to be analyzed with spatio-temporal precision. To this end, optogenetic approaches and genetically encoded fluorescent biosensors are particularly well suited. Synthesis and hydrolysis of cAMP can be directly manipulated by photoactivated adenylyl cyclases (PACs) and light-regulated phosphodiesterases (PDEs), respectively. In addition, many biosensors have been designed to spatially and temporarily resolve cAMP dynamics in the cell. This review provides an overview about optogenetic tools and biosensors to shed light on the subcellular organization of cAMP signaling.

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