Horse heart myoglobin catalyzes the H2O2-dependent oxidative dehalogenation of chlorophenols to DNA-binding radicals and quinones.

The research examines how myoglobin, a protein in horse hearts, demonstrates peroxidase-like activity in circumstances of oxidative stress, which allows it to oxidize and transform certain carcinogenic halophenols – with promising insights into why these compounds might be cancer-causing.

Objectives and Method of the Research

• The research aims to study the behavior of myoglobin (Mb), a respiratory protein found in horse hearts, in situations of oxidative stress – particularly its ability to exhibit peroxidase-like activity.
• The investigators achieve this by observing myoglobin’s reactions with H2O2 or other peroxides, leading to the generation of a heme intermediate, ferryl [Fe(IV)=O] Compound II (Cpd II).
• The researchers then examine how this Cpd II catalyzes the oxidation of carcinogenic halophenols, namely, converting 2,4,6-trichlorophenol (TCP) into 2,6-dichloro-1,4-benzoquinone.

Findings and Implications

• An important finding from the study is that myoglobin Cpd II is an active oxidant in halophenol dehalogenation, underlining a traditional peroxidase process of adding H2O2 before TCP.
• Moreover, with 4-chlorophenol, a product formed upon dimerization backs a mechanism involving the creation of a reactive phenoxy radical intermediate via an electron transfer technique.
• This radical nature may have physiological significance considering that phenoxy radicals and electrophilic quinones covalently bind to DNA, as evident from other recent research.
• Consequently, the stability of myoglobin Cpd II, along with its capacity to oxidize TCP, may offer insights into why such compounds are carcinogenic. The research suggests that the interaction between myoglobin and these carcinogenic compounds may trigger radical reactions leading to DNA binding – a known cause of carcinogenesis.
• The markers also reveal that the initial rate of dehalogenation activated by myoglobin Cpd II is almost similar to that of the same response carried out by the ferric state’s turnover, which outlines the potential physiological hazards of such enduring, high-valent intermediates.