Chlorophyll-mediated energy capture in animal mitochondria

Obtaining energy from the environment is fundamental to all forms of life, but only photosynthetic organisms are able to directly capture sunlight and convert it into biological energy as ATP, e.g. through light-absorbing chlorophyll molecules of plant chloroplasts. With their diet, animals take up chlorophyll, which is then converted into different metabolites that retain the ability to absorb light at wavelengths that can penetrate into animal tissues. But what are the consequences of light absorption by these metabolites? In this study (p.388), Ilyas Washington and colleagues address this question by assessing the function of chlorophyll metabolites in Caenorhabditis elegans and in mice. They find that addition of the light-capturing chlorophyll metabolite pyropheophorbide-a (P-a) to the animal diet leads to it entering the circulation and becoming enriched in mitochondria; there, it results in higher concentration of ATP when the animals are exposed to light. The authors also show that P-a extends the life span of C. elegans that are exposed to light. With regard to the molecular mechanism, the biochemical experiments performed here suggest that P-a modulates the mitochondrial ATP stores by catalysing the reduction of coenzyme Q – a slow step in ATP synthesis. Taken together, the data presented here suggest that, similarly to plants and photosynthetic organisms, animals also possess metabolic pathways to derive energy directly from sunlight.