“Alternative” fuels contributing to mitochondrial electron transport: Importance of non-classical pathways in the diversity of animal metabolism

Abstract The study of glycolysis, the TCA cycle, and oxidative phosphorylationin animalshas yielded a wealth of information about bioenergetics. Less is known about how animalsuse fuels other than glucose and less characterized enzymes that are also used to provide electrons to the electron transport system. It has become clear that bioenergeticflexibility is employed by a wide variety of animalsin order to successfully grow, maintain cells, and reproduce, and has contributed to the exploitation of new environments and ecological nichesthrough evolution. In most cases, the discovery of these “alternative” fuels and non-classical pathways is relatively recent, but is starting to call into question long believed paradigms about the diversity of animal bioenergetics. We present several specific examples of these “alternatives” and the animalsthat use them and present some implications for animalmitochondrial physiology research.