Vanadium Chloroperoxidases: The Missing Link in the Formation of Chlorinated Compounds and Chloroform in the Terrestrial Environment?

5 years ago

Vanadium Chloroperoxidases: The Missing Link in the Formation of Chlorinated Compounds and Chloroform in the Terrestrial Environment?

Ron Wever, Phil Barnett

It is well established that the majority of chlorinated organic substances found in the terrestrial environment are produced naturally. The presence of these compounds in soils is not limited to a single ecosystem. Natural chlorination is also a widespread phenomenon in grasslands and agricultural soils typical for unforested areas. These chlorinated compounds are formed from chlorination of natural organic matter consisting of very complex chemical structures, such as lignin. Chlorination of several lignin model compounds results in the intermediate formation of trichloroacetyl-containing compounds, which are also found in soils. These decay, in general, through a haloform-type reaction mechanism to CHCl3. Upon release into the atmosphere, CHCl3 will produce chlorine radicals through photolysis, which will, in turn, lead to natural depletion of ozone. There is evidence that fungal chloroperoxidases able to produce HOCl are involved in the chlorination of natural organic matter. The objective of this review is to clarify the role and source of the various chloroperoxidases involved in the natural formation of CHCl3. Fungal secretions: Two classes of enzymes of fungal origin are involved in the formation of natural organochlorines, heme chloroperoxidases (CPOs) and vanadium CPOs. The underexposed role of vanadium CPOs produced by plant pathogenic fungi is highlighted. These unusually stable enzymes form bleach, which reacts with natural organic matter to form organochlorines present in almost all soils. These compounds decay to chloroform, which is released to the stratosphere (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/asia.201700420