Phytogenesis of halomethanes: A product ofselection or a metabolic accident?
- Cite this article as:
- Manley, S.L. Biogeochemistry (2002) 60: 163. doi:10.1023/A:1019859922489
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Phytoplankton (microalgae), seaweeds(macroalgae), higher plants and fungi producehalomethanes. Algae and fungi produce bothmethyl halides and polyhalomethanes, whereasplants are known to produce only methylhalides. Why these organisms producehalomethanes is a question frequently asked bychemists and biologists. This question impliesthat halomethanes have a function and have aselective value to the producing organism.Except for some fungi, the evolutionaryadvantage of producing halomethanes may notpresently exist. Polyhalomethanes areby-products of halogenation of certain organiccompounds by haloperoxidases in marine algaeand perhaps some fungi, and they may beindirectly produced in aquatic environments byalgal release of oxidized halogen species. Amain function of this enzyme is to rid the cellof harmful oxidants such as hydrogen peroxide.Monohalomethanes (methyl halides) are productsof methyltransferase activity. It has beenproposed that methyl halide production mayprovide a mechanism to regulate chloride levelsin halotolerant plants. The examination of halidecellular concentrations, halomethane productionrates, and enzyme characteristics raisesquestions about this possible function. Inalgae, plants and some fungi, methyl halidesmay be a result of the insertion of ubiquitoushalides into the active site of numerousmethyltransferases. Therefore, halomethanes maybe by-products or `accidents' of metabolism.