Some Biochemical Reactions of Alkanes

Alkanes occur naturally in places other than petroleum deposits. In insects, for example. The waxy alkanes dispersed in its cuticle help protect an insect from dehydration. Some insects use volatile alkanes to defend themselves or communicate with others of the same species. Alkanes even serve as starting materials that the insect converts to other biologically important substances. 

The major biosynthetic pathway leading to alkanes is by enzyme-catalyzed decarboxylation (loss of CO2) of fatty acids, compounds of the type CH3(CH2) C02H in which n is an even number and the chain has 14 or more carbons. 

Biochemical conversion of alkanes to other substances normally begins with oxidation. 

In addition to alkanes, the oxidation of drugs and other substances occurs mainly in the liver and is catalyzed by the enzyme cytochrome P-450. Molecular oxygen and nicotinamide adenine dinucleotide (NAD) are also required. 

Reactions of this type also occur in insects but are not limited to them. Oxidation by microorganisms has been extensively studied and is often selective for certain kinds of C—H bonds. The fungus Pseudomonas oleovorans, for example, oxidizes the CH3 groups at the end of the carbon chain of 4-methyloctane faster than the CH3 branch and faster than the CH2 and CH units within the chain. 

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Despite this, anaerobes offer rewards to those who persevere by providing for the discovery of the most novel biochemical reactions on Earth. Some of these reactions have recently been elucidated. For example, bacteria are now known to cataboHze toluene anaerobically. They initiate attack on the benzyHc carbon via a radical mechanism that generates a new carbon-carbon bond to form benzylsuccinate as the first metabolite (Leuthner et al. 1998). Others, such as the anaerobic formation of methane from long-chain alkanes (Zengler et al. 1999), remain obscme biochemically. 

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