Cell Biology

Seamlessly Hemeless

See allHide authors and affiliations

Science  16 Mar 2012:
Vol. 335, Issue 6074, pp. 1281
DOI: 10.1126/science.335.6074.1281-a

Hemoproteins are ubiquitous and are required, for example, in respiratory chains, redox reactions, signal transduction, and oxygen transport and sensing. Until now, no eukaryote has been identified that can survive without heme. Kořený et al. have discovered a group of evolutionary outliers that defy the omnipresent heme. Phytomonas serpens is a plant-parasitic kinetoplastid that has no essential heme-containing macromolecules and a rather odd physiology as a result. The only heme biosynthesis gene Phytomonas possesses is ferrochelatase, and it has no respiratory cytochromes, even though it can reoxidize NADH produced during glycolysis, and succinate dehydrogenase still assembles into a functional entity able to reduce ubiquinone. The sugar-rich environment of plant sap allows the organism to bypass the heme requirement for proton pumping, via the non-heme iron of the alternative terminal oxidase. Even in this extreme example, there is enough functional redundancy in the range of cellular processes to allow life to proceed uninterrupted, and Phytomonas throws considerable light on potentially undiscovered links and pathways.

Proc. Natl. Acad. Sci. U.S.A. 109, 10.1073/pnas.1201089109 (2012).

Navigate This Article