15-Methylhexadecanoic acid is present in many plants, animals, and other organisms and has a central role in the biosynthesis of other iso-fatty acids in Stigmatella aurantiaca.1 In bacteria, the iso-fatty acid2 content and composition can often be used as a taxonomic marker3 because iso-fatty acids are often found in bacteria but not commonly in other microorganisms. Some bacteria have iso- but not anteiso-fatty acids while others have anteiso- but not iso-fatty acids. Isofatty acids are found in small amounts in marine organisms and ruminants, mainly due to the food chain but also due to some de novo synthesis. Iso-fatty acids with a total even number of carbons are more common than a total odd number. Some waxy materials such as lanolin, as well as secretions near animal eyes, contain an unusually high amount of iso-fatty acids being employed for their lubricating effect. Branched chain fatty acids are critical for the regulation of fluidity in membranes and in membrane transport for many types of bacteria due to their having a significantly lower transition temperature than straight chain fatty acids. Some bacteria handle stress (such as heat and toxicity) by changing the ratio of anteiso/iso-fatty acids in the cell membrane. Iso-fatty acids have been found to be activators for various enzymes and systems and are used as protein modifiers. Although iso-even chain fatty acids are commonly derived from isobutyryl-CoA some bacteria derive all iso-even chain fatty acids via alpha-oxidation of iso-odd chain fatty acids.4 While iso-fatty acids are not usually found in plant oils the waxy surface of leaves can contain significant amounts of these fatty acids.
