Kinetic studies on the reaction between dicyanocobinamide and hypochlorous acid

Hypochlorous acid (HOCl) is a potent oxidant generated by myeloperoxidase (MPO), which is an abundant enzyme used for defense against microbes. We examined the potential role of HOCl in corrin ring destruction and subsequent formation of cyanogen chloride (CNCl) from dicyanocobinamide ((CN)2-Cbi). S...

Full description

Saved in:
Bibliographic Details
Published in:PloS one 2014-11, Vol.9 (11), p.e110595-e110595
Main Authors: Maitra, Dhiman, Ali, Iyad, Abdulridha, Rasha M, Shaeib, Faten, Khan, Sana N, Saed, Ghassan M, Pennathur, Subramaniam, Abu-Soud, Husam M
Format: Article
Language:English
Subjects:
Acids
Analysis
Biochemistry
Biology and Life Sciences
Chemistry
Cobalt
Constants
Cyanides
Cyanides - chemistry
Cyanogen
Destruction
Enzymes
Gynecology
Hydrogen-Ion Concentration
Hypochlorous acid
Hypochlorous Acid - chemistry
Inflammatory diseases
Inorganic chemistry
Intermediates
Kinetics
Ligands
Medicine
Nitriles
Nitriles - chemistry
Obstetrics
Organometallic Compounds - chemistry
Peroxidase
Rate constants
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Hypochlorous acid (HOCl) is a potent oxidant generated by myeloperoxidase (MPO), which is an abundant enzyme used for defense against microbes. We examined the potential role of HOCl in corrin ring destruction and subsequent formation of cyanogen chloride (CNCl) from dicyanocobinamide ((CN)2-Cbi). Stopped-flow analysis revealed that the reaction consists of at least three observable steps, including at least two sequential transient intermediates prior to corrin ring destruction. The first two steps were attributed to sequential replacement of the two cyanide ligands with hypochlorite, while the third step was the destruction of the corrin ring. The formation of (OCl)(CN)-Cbi and its conversion to (OCl)2-Cbi was fitted to a first order rate equation with second order rate constants of 0.002 and 0.0002 µM(-1) s(-1), respectively. The significantly lower rate of the second step compared to the first suggests that the replacement of the first cyanide molecule by hypochlorite causes an alteration in the ligand trans effects changing the affinity and/or accessibility of Co toward hypochlorite. Plots of the apparent rate constants as a function of HOCl concentration for all the three steps were linear with Y-intercepts close to zero, indicating that HOCl binds in an irreversible one-step mechanism. Collectively, these results illustrate functional differences in the corrin ring environments toward binding of diatomic ligands.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0110595