scholarly journals Protein hydroperoxides can give rise to reactive free radicals

1995 ◽  
Vol 305 (2) ◽  
pp. 643-649 ◽  
Author(s):  
M J Davies ◽  
S Fu ◽  
R T Dean
Keyword(s):  
Free Radicals ◽  
Amino Acid ◽  
Radical Anion ◽  
Similar Process ◽  
Side Chain ◽  
Radical Species ◽  
Radical Chain ◽  
Chain Reactions ◽  
Oxygen Yield ◽  
Rearrangement Processes

Proteins damaged by free-radical-generating systems in the presence of oxygen yield relatively long-lived protein hydroperoxides. These hydroperoxides have been shown by e.p.r. spectroscopy to be readily degraded to reactive free radicals on reaction with iron(II) complexes. Comparison of the observed spectra with those obtained with free amino acid hydroperoxides had allowed identification of some of the protein-derived radical species (including a number of carbon-centred radicals, alkoxyl radicals and a species believed to be the CO2 radical anion) and the elucidation of novel fragmentation and rearrangement processes involving amino acid side chains. In particular, degradation of hydroperoxide functions on the side chain of glutamic acid is shown to result in decarboxylation at the side-chain carboxy group via the formation of the CO2 radical anion; the generation of an identical radical from hydroperoxide groups on proteins suggests that a similar process occurs with these molecules. In a number of cases these fragmentation and rearrangement reactions give rise to further reactive free radicals (R., O2-./HO2., CO2-.) which may act as chain-carrying species in protein oxidations. These studies suggest that protein hydroperoxides are capable of initiating further radical chain reactions both intra- and inter-molecularly, and provide information on some of the fundamental mechanisms of protein alteration and side-chain fragmentation.

scholarly journals Vitamin E in Human Health and Oxidative Stress Related Diseases

2021 ◽  
Author(s):  
Israel Ehizuelen Ebhohimen ◽  
Taiwo Stephen Okanlawon ◽  
Augustine Ododo Osagie ◽  
Owen Norma Izevbigie
Keyword(s):  
Oxidative Stress ◽  
Free Radicals ◽  
Vitamin E ◽  
Oxidative Process ◽  
Radical Species ◽  
Radical Chain ◽  
Chain Reactions ◽  
Hydrophobic Nature ◽  
Antioxidant Mechanisms ◽  
And Oxidative Stress

Oxidative stress characterized by an imbalance in the production and degradation of radical species has been implicated in the onset and progression of several diseases. The efficacy of antioxidants acting via the inhibition of radical chain reactions, scavenging of free radicals, direct donation of electrons to radical species and chelation of metal ions have been reported to attenuate the oxidative process. Vitamin E is an effective antioxidant and its hydrophobic nature and membrane permeability offer some benefits to application and bioavailability. This chapter highlights the following; structural differences in the vitamin family, biosynthesis in plants and the native biological role, antioxidant mechanisms of vitamin E, an overview of the prophylactic action of vitamin E as well as the effect on the oxidative process in some diseases.

Electrogeneration of Triphenyltin Radical, Anion, and Cation. Electrochemical Initiation of Tin Hydride-Promoted Radical Chain Reactions

1996 ◽  
Vol 61 (26) ◽  
pp. 9402-9408 ◽  
Author(s):  
Hideo Tanaka ◽  
Hidenori Ogawa ◽  
Hiroaki Suga ◽  
Sigeru Torii ◽  
Anny Jutand ◽  
...  
Keyword(s):  
Radical Anion ◽  
Radical Chain ◽  
Chain Reactions

Bactericidal Activities of Radical Species Generated by Catalytic Reaction of Iron(III) Octacarboxyphthalocyanine

1998 ◽  
Vol 02 (02) ◽  
pp. 101-106 ◽  
Author(s):  
TAKASHI ICHINOHE ◽  
MAKOTO MIYAJIMA ◽  
YASUHISA NOGUCHI ◽  
MASAHIKO ITO ◽  
MUTSUMI KIMURA ◽  
...  
Keyword(s):  
Reaction System ◽  
Catalytic Decomposition ◽  
Order Rate Constant ◽  
Second Order ◽  
Methyl Radical ◽  
Radical Species ◽  
Radical Chain ◽  
Chain Reactions ◽  
Bactericidal Activities ◽  
Resonance Spin

Strong bactericidal activities against various bacteria were observed in the reaction system of iron(III) octacarboxyphthalocyanine ( Fe III - oapc ) and tert-butyl hydroperoxide (tert-BuOOH). The kinetics of the decomposition of tert-BuOOH catalysed by Fe III -oapc were studied in buffered solutions between pH 5 to 12 using gas chromatography analysis. The rate of catalytic decomposition of tert-BuOOH followed second-order kinetics in tert-BuOOH concentrations. The second-order rate constant (k2) had a maximum value at pH 11. Oxygen evolution was observed at high tert-BuOOH concentration, while oxygen consumption was observed at low tert-BuOOH concentration. The former indicates plural radical chain reactions of the tert-butoxyl radical and the latter suggests decomposition of the tert-butoxyl radical to acetone and methyl radical. By the electron spin resonance spin trapping method using 5,5-dimethyl-1-pyrroline-N-oxide and α-phenyl-N-tert-butylnitrone it was found that the radical species generated in the reaction system is tert-butoxyl radical, which plays crucial roles in bactericidal activities.

Polypeptides Folding: Rules for the Calculation of the Backbone Dihedral Angles φ starting from the Amino Acid Sequence

2020 ◽  
Author(s):  
Michele Larocca
Keyword(s):  
Amino Acid ◽  
Amino Acid Sequence ◽  
Theoretical Approach ◽  
Polypeptide Chain ◽  
Hydrophobic Effect ◽  
Side Chain ◽  
Dihedral Angles ◽  
Mechanical Forces ◽  
Specific Chemical

<p>Protein folding is strictly related to the determination of the backbone dihedral angles and depends on the information contained in the amino acid sequence as well as on the hydrophobic effect. To date, the type of information embedded in the amino acid sequence has not yet been revealed. The present study deals with these problematics and aims to furnish a possible explanation of the information contained in the amino acid sequence, showing and reporting rules to calculate the backbone dihedral angles φ. The study is based on the development of mechanical forces once specific chemical interactions are established among the side chain of the residues in a polypeptide chain. It aims to furnish a theoretical approach to predict backbone dihedral angles which, in the future, may be applied to computational developments focused on the prediction of polypeptide structures.</p>

Schistosomal Sulfotransferase Interaction with Oxamniquine Involves Hybrid Mechanism of Induced-fit and Conformational Selection

2020 ◽  
Vol 16 (4) ◽  
pp. 451-459 ◽  
Author(s):  
Fortunatus C. Ezebuo ◽  
Ikemefuna C. Uzochukwu
Keyword(s):  
Molecular Dynamics ◽  
Amino Acid ◽  
Binding Energy ◽  
Binding Site ◽  
Conformational Dynamics ◽  
Side Chain ◽  
Amino Acid Residues ◽  
Conformational Selection ◽  
Hybrid Mechanism ◽  
Dynamics Simulations

Background: Sulfotransferase family comprises key enzymes involved in drug metabolism. Oxamniquine is a pro-drug converted into its active form by schistosomal sulfotransferase. The conformational dynamics of side-chain amino acid residues at the binding site of schistosomal sulfotransferase towards activation of oxamniquine has not received attention. Objective: The study investigated the conformational dynamics of binding site residues in free and oxamniquine bound schistosomal sulfotransferase systems and their contribution to the mechanism of oxamniquine activation by schistosomal sulfotransferase using molecular dynamics simulations and binding energy calculations. Methods: Schistosomal sulfotransferase was obtained from Protein Data Bank and both the free and oxamniquine bound forms were subjected to molecular dynamics simulations using GROMACS-4.5.5 after modeling it’s missing amino acid residues with SWISS-MODEL. Amino acid residues at its binding site for oxamniquine was determined and used for Principal Component Analysis and calculations of side-chain dihedrals. In addition, binding energy of the oxamniquine bound system was calculated using g_MMPBSA. Results: The results showed that binding site amino acid residues in free and oxamniquine bound sulfotransferase sampled different conformational space involving several rotameric states. Importantly, Phe45, Ile145 and Leu241 generated newly induced conformations, whereas Phe41 exhibited shift in equilibrium of its conformational distribution. In addition, the result showed binding energy of -130.091 ± 8.800 KJ/mol and Phe45 contributed -9.8576 KJ/mol. Conclusion: The results showed that schistosomal sulfotransferase binds oxamniquine by relying on hybrid mechanism of induced fit and conformational selection models. The findings offer new insight into sulfotransferase engineering and design of new drugs that target sulfotransferase.

Synthesis and conformation of sequential basic polypeptides with branched and linear side chains

1985 ◽  
Vol 50 (12) ◽  
pp. 2925-2936 ◽  
Author(s):  
Štěpánka Štokrová ◽  
Jan Pospíšek ◽  
Jaroslav Šponar ◽  
Karel Bláha
Keyword(s):  
Amino Acid ◽  
Salt Concentration ◽  
Salt Solution ◽  
Theoretical Work ◽  
Side Chain ◽  
Amino Acid Residues ◽  
Cd Spectra ◽  
Low Salt ◽  
Conformational Freedom ◽  
Basic Polypeptides

Polypeptides (Lys-X-Ala)n and (Lys-X-Gly)n in which X represents residues of isoleucine and norleucine, respectively, and polypeptide (Tle-Lys-Ala)n, were synthesized via polymerization of 1-hydroxysuccinimidyl esters of the appropriate tripeptides to complete previously studied series. Circular dichroism (CD) spectra of the respective polymers were measured as a function of pH and salt concentration of the medium. The results were correlated with those obtained previously with the same series containing different amino acid residues at the X-position. The helix forming ability of the polypeptides (Lys-X-Ala)n with linear X side chain was found to be independent of the length. In the series (Lys-X-Gly)n the unordered conformation was the most probable one except (Lys-Ile-Gly)n. This polymer assumed the β conformation even in low salt solution at neutral pH. An agreement with some theoretical work concerned with the restriction of conformational freedom of amino acid residue branching at Cβ atom with our experimental results is evident.

Comparison of the Potency of 8-L-Arginine, 8-D-Arginine and 8-D-Homoarginine Vasopressin Analogs with Substituted Phenylalanine in Position 2

1994 ◽  
Vol 59 (6) ◽  
pp. 1439-1450 ◽  
Author(s):  
Miroslava Žertová ◽  
Jiřina Slaninová ◽  
Zdenko Procházka
Keyword(s):  
Amino Acid ◽  
Solid Phase Synthesis ◽  
Solid Phase ◽  
Basic Amino Acid ◽  
The Other ◽  
Side Chain ◽  
Inhibitory Potency ◽  
Phase Synthesis ◽  
Other Hand ◽  
Order Of Magnitude

An analysis of the uterotonic potencies of all analogs having substituted L- or D-tyrosine or -phenylalanine in position 2 and L-arginine, D-arginine or D-homoarginine in position 8 was made. The series of analogs already published was completed by the solid phase synthesis of ten new analogs having L- or D-Phe, L- or D-Phe(2-Et), L- or D-Phe(2,4,6-triMe) or D-Tyr(Me) in position 2 and either L- or D-arginine in position 8. All newly synthesized analogs were found to be uterotonic inhibitors. Deamination increases both the agonistic and antagonistic potency. In the case of phenylalanine analogs the change of configuration from L to D in position 2 enhances the uterotonic inhibition for more than 1 order of magnitude. The L to D change in position 8 enhances the inhibitory potency negligibly. Prolongation of the side chain of the D-basic amino acid in position 8 seems to decrease slightly the inhibitory potency if there is L-substituted amino acid in position 2. On the other hand there is a tendency to the increase of the inhibitory potency if there is D-substituted amino acid in position 2.

Analogues of the cholecystokinin octapeptide modified in the central part of the molecule

1991 ◽  
Vol 56 (9) ◽  
pp. 1963-1970 ◽  
Author(s):  
Jan Hlaváček ◽  
Václav Čeřovský ◽  
Jana Pírková ◽  
Pavel Majer ◽  
Lenka Maletínská ◽  
...  
Keyword(s):  
Amino Acid ◽  
Biological Activities ◽  
Point Of View ◽  
Biologically Active ◽  
Side Chain ◽  
Amino Acid Residues ◽  
Cholecystokinin Octapeptide ◽  
Biological Tests ◽  
Biological Potency ◽  
Biologically Active Conformation

In a series of analogues of the cholecystokinin octapeptide (CCK-8) the amino acid residues were gradually modified by substituting Gly by Pro in position 4, Trp by His in position 5, Met by Cle in position 6, or the Gly residue was inserted between Tyr and Met in positions 2 and 3 of the peptide chain, and in the case of the cholecystokinin heptapeptide (CCK-7) the Met residues were substituted by Nle or Aib. These peptides were investigated from the point of view of their biological potency in the peripheral and central region. From the results of the biological tests it follows that the modifications carried out in these analogues and in their Nα-Boc derivatives mean a suppression of the investigated biological activities by 2-3 orders of magnitude (at a maximum dose of the tested substance of 2 . 10-2 mg per animal).This means that a disturbance of the assumed biologically active conformation of CCK-8, connected with a considerable decrease of the biological potency of the molecule, takes place not only after introduction of the side chain into its centre (substitution of Gly4), but also after the modification of the side chains of the amino acids or by extension of the backbone in further positions around this central amino acid.

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