A study suggests that tropical cyclones have been increasing in intensity over the past four decades, consistent with predictions of physical theory and numerical simulations.
Image credit: NOAA/NASA.
New Research In
Physical Sciences
Featured Portals
Articles by Topic
Biological Sciences
Featured Portals
Articles by Topic
Edited by Rowena G. Matthews, University of Michigan, Ann Arbor, MI, and approved August 18, 2011 (received for review May 25, 2011)
Abstract
Modified tetrapyrroles such as chlorophyll, heme, siroheme, vitamin B12, coenzyme F430, and heme d1 underpin a wide range of essential biological functions in all domains of life, and it is therefore surprising that the syntheses of many of these life pigments remain poorly understood. It is known that the construction of the central molecular framework of modified tetrapyrroles is mediated via a common, core pathway. Herein a further branch of the modified tetrapyrrole biosynthesis pathway is described in denitrifying and sulfate-reducing bacteria as well as the Archaea. This process entails the hijacking of siroheme, the prosthetic group of sulfite and nitrite reductase, and its processing into heme and d1 heme. The initial step in these transformations involves the decarboxylation of siroheme to give didecarboxysiroheme. For d1 heme synthesis this intermediate has to undergo the replacement of two propionate side chains with oxygen functionalities and the introduction of a double bond into a further peripheral side chain. For heme synthesis didecarboxysiroheme is converted into Fe-coproporphyrin by oxidative loss of two acetic acid side chains. Fe-coproporphyrin is then transformed into heme by the oxidative decarboxylation of two propionate side chains. The mechanisms of these reactions are discussed and the evolutionary significance of another role for siroheme is examined.
Footnotes
- 1To whom correspondence may be addressed. E-mail: m.j.warren{at}kent.ac.uk or stuart.ferguson{at}bioch.ox.ac.uk.
Author contributions: S.B., A.D.L., S.A.L., L.M.S., S.J.F., and M.J.W. designed research; S.B., A.D.L., S.A.L., D.J.P., and M.J.H. performed research; S.B., A.D.L., S.A.L., B.T.G., and M.J.H. analyzed data; and S.B., L.M.S., B.T.G., S.J.F., and M.J.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1108228108/-/DCSupplemental.
Molecular hijacking of siroheme for the synthesis of heme and d1 heme
Sign up for Article Alerts
Jump to section
You May Also be Interested in
Atomic-scale analysis of the Tagish Lake meteorite finds that its raspberry-like magnetite grains formed in a sodium-rich, high-pH environment, providing insight into the chemistry of the earliest fluids in the Solar System.
Image credit: Chi Ma.
Bayesian analysis of the chronology of life’s emergence and development on Earth suggests that if Earth’s history were repeated, the emergence of intelligence might be a sufficiently rare event that it would not be guaranteed to reoccur.
Image credit: NASA Earth Observatory image by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA's Goddard Space Flight Center.
Profile of NAS member and biochemist Edward H. Egelman.
Some governments are using the pandemic as a smokescreen to eviscerate regulations. Meanwhile, deforestation is spiking along with COVID-19.