scholarly journals Anaerobic and aerobic coproporphyrinogen III oxidases of Rhodopseudomonas spheroides. Mechanism and stereochemistry of vinyl group formation

1983 ◽  
Vol 209 (3) ◽  
pp. 709-718 ◽  
Author(s):  
J S Seehra ◽  
P M Jordan ◽  
M Akhtar
Keyword(s):  
Hydrogen Atom ◽  
Group Formation ◽  
Side Chains ◽  
Improved Method ◽  
Conversion Formula ◽  
Coproporphyrinogen Iii Oxidase ◽  
Rhodopseudomonas Spheroides ◽  
Vinyl Group

An improved method for the preparation of various species of porphobilinogen stereospecifically labelled with 3H in the side chains (at C-6, C-7 and C-8) is described. These labelled samples were used to study the mechanism and stereochemistry of anaerobic as well as aerobic coproporphyrinogen III oxidase of light-grown Rhodopseudomonas spheroides. It was shown that both the oxidases catalyse the conversion of the propionate side chains of coproporphyrinogen III into the vinyl groups of protoporphyrinogen IX, (formula; see text) with the labilization of the pro-S-hydrogen atom at the beta-position. These results are similar to those previously recorded for such conversions in animal and plant systems. In the light of the cumulative information available to date, mechanisms for the conversion, (formula; see text) are discussed and doubt is cast on the participation of hydroxylated intermediates in the process.

Self-branching in the polymerization of vinyl acetate

1954 ◽  
Vol 221 (1147) ◽  
pp. 437-452 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Vinyl Acetate ◽  
Small Molecule ◽  
Radioactive Isotope ◽  
Average Length ◽  
Polymer Molecule ◽  
Side Chains ◽  
Carbon 14 ◽  
Inactive Monomer ◽  
Number Of Branches

Polyvinylacetate labelled with the radioactive isotope carbon-14 has been used to study the reactions by which side-chains are introduced into polyvinylacetate. It is believed that the first stage in the growth of a branch is the process of ‘transfer to polymer’ in which a growing radical abstracts a hydrogen atom from a polymer molecule so forming a new reactive point along the length of the molecule. Inactive monomer was polymerized in the presence of radioactive polymer and from the product was isolated material consisting of the original active polymer with inactive side-chains grafted on it. It was possible to calculate the number of branches and their average length and also to determine the value for the velocity constant for the process of ‘transfer to polymer’. It was found that the abstraction of a hydrogen atom from a dead polymer molecule by a polyvinylacetate radical occurs at a rate very similar to that with which the radical abstracts a hydrogen atom from a small molecule.

Evolution thermique de N-oxydes de dimethylamino-5 alcanols-1 substitues en 5. Competition entre rearrangements de cope et de Meisenheimer

1985 ◽  
Vol 50 (4) ◽  
pp. 956-961
Author(s):  
Didier Barbry ◽  
Bruno Hasiak ◽  
Jean-Michel Augait ◽  
Daniel Couturier
Keyword(s):  
Hydrogen Atom ◽  
Statistical Distribution ◽  
Methyl Ethyl ◽  
Phenyl Substituent ◽  
Electronic Effects ◽  
Vinyl Group ◽  
Acidic Hydrogen

The effect of the substituent R in the position was studied in the decomposition of 1,5-aminoalcohol N-oxides: Meisenheimer rearrangement takes place when R is the vinyl group but is not observed with the phenyl substituent; elimination to alkenol only affects the more acidic hydrogen atom when R is the allyl or benzyl group; with substituents inducing less important electronic effects (methyl, ethyl), the reaction yields an alkenols mixture with statistical distribution.

Hydrogen atom attachment to histidine and tryptophan containing peptides in the gas phase

2019 ◽  
Vol 21 (22) ◽  
pp. 11633-11641 ◽  
Author(s):  
Daiki Asakawa ◽  
Hidenori Takahashi ◽  
Shinichi Iwamoto ◽  
Koichi Tanaka
Keyword(s):  
Hydrogen Atom ◽  
Gas Phase ◽  
Bond Cleavage ◽  
Tryptophan Residue ◽  
Side Chains ◽  
Hydrogen Atoms ◽  
Fragment Ions ◽  
Gas Phase Fragmentation

In this study, we focus on the gas-phase fragmentation induced by the attachment of hydrogen atoms to the histidine and tryptophan residue side-chains in the peptide that provides the fragment ions due to Cα–Cβ bond cleavage.

scholarly journals The oxygen-independent coproporphyrinogen III oxidase HemN utilizes harderoporphyrinogen as a reaction intermediate during conversion of coproporphyrinogen III to protoporphyrinogen IX

2010 ◽  
Vol 391 (1) ◽  
Author(s):  
Katrin Rand ◽  
Claudia Noll ◽  
Hans Martin Schiebel ◽  
Dorit Kemken ◽  
Thomas Dülcks ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Hplc Analysis ◽  
Heme Biosynthesis ◽  
Chromatographic Behavior ◽  
Side Chain ◽  
Oxidative Decarboxylation ◽  
Side Chains ◽  
Reaction Intermediate ◽  
Coproporphyrinogen Iii Oxidase

Abstract During heme biosynthesis the oxygen-independent coproporphyrinogen III oxidase HemN catalyzes the oxidative decarboxylation of the two propionate side chains on rings A and B of coproporphyrinogen III to the corresponding vinyl groups to yield protoporphyrinogen IX. Here, the sequence of the two decarboxylation steps during HemN catalysis was investigated. A reaction intermediate of HemN activity was isolated by HPLC analysis and identified as monovinyltripropionic acid porphyrin by mass spectrometry. This monovinylic reaction intermediate exhibited identical chromatographic behavior during HPLC analysis as harderoporphyrin (3-vinyl-8,13,17-tripropionic acid-2,7,12,18-tetramethylporphyrin). Furthermore, HemN was able to utilize chemically synthesized harderoporphyrinogen as substrate and converted it to protoporphyrinogen IX. These results suggest that during HemN catalysis the propionate side chain of ring A of coproporphyrinogen III is decarboxylated prior to that of ring B.

scholarly journals Structure and thermal interconversion of cyclobilirubin IX α

1984 ◽  
Vol 218 (3) ◽  
pp. 667-676 ◽  
Author(s):  
S Onishi ◽  
I Miura ◽  
K Isobe ◽  
S Itoh ◽  
T Ogino ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Chemical Structure ◽  
Lactone Ring ◽  
Final Conclusion ◽  
Quaternary Carbon Atom ◽  
Methyl Group ◽  
Bilirubin Metabolism ◽  
To Come ◽  
Vinyl Group

One of the two main photoproducts in bilirubin metabolism during phototherapy in neonatal hyperbilirubinaemia is (EZ)-cyclobilirubin. However, it has not yet been possible to come to a final conclusion as to its chemical structure, despite the fact that much effort has been expended on the problem. The present paper demonstrates that (EZ)-cyclobilirubin is formed by the intramolecular cyclization of the C-3-vinyl group with the position at C-7 rather than at C-6, without delta-lactone-ring formation. The evidence comes from 13C-n.m.r. spectra, which indicate that an oxygen-bound quaternary carbon atom is not present, and from 1H-n.m.r. spectra, which indicate that the orientation of the methyl group at C-2 is equatorial; these findings are supported by mass spectra. The existence of both an epimeric relationship at C-7 between (EE)- and (EZ)-cyclobilirubins A and B and of steric isomers of the hydrogen atom and methyl group at C-2 is supported by the fact that the methyl-group protons at C-2 and C-7 are observed as a paired signal in 1H-n.m.r. spectra, and that new signals at C-7, C-2 and C-3 beta appear in 13C-n.m.r. spectra, that mass spectra of (EZ)-cyclobilirubins A and B are extremely similar and that, furthermore, thermal interconversion between (EE)- and (EZ)-cyclobilirubins A and B is observed.

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