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Oxidative Cleavage of Alkenes: Ozonolysis01:46

Oxidative Cleavage of Alkenes: Ozonolysis

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Peroxisomes01:24

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Anaerobic Protein Purification and Kinetic Analysis via Oxygen Electrode for Studying DesB Dioxygenase Activity and Inhibition
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Published on: October 3, 2018

Steroids, triterpenoids and molecular oxygen.

Roger E Summons1, Alexander S Bradley, Linda L Jahnke

  • 1Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Avenue E34-246, Cambridge, MA 02139-4307, USA. rsummons@mit.edu

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
|June 7, 2006
PubMed
Summary

Steroid and triterpenoid biomarkers indicate ancient oxygenic photosynthesis. This study reviews their biosynthesis, finding sterol pathways likely evolved with eukaryotes, not anaerobically, and are not found in cyanobacteria.

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Area of Science:

  • Biogeochemistry
  • Molecular Evolution
  • Paleobiology

Background:

  • Triterpenoid biomarkers are linked to environmental oxygen levels, inferring ancient oxygenic photosynthesis.
  • The origin and evolutionary pathways of steroid and triterpenoid biosynthesis remain debated.
  • Understanding these pathways is crucial for interpreting Earth's early biochemical history.

Purpose of the Study:

  • To review the oxygen requirements for steroid biosynthesis.
  • To examine phylogenetic patterns in steroid and triterpenoid biosynthetic pathways.
  • To assess the antiquity of aerobic steroid production and its implications for early life.

Main Methods:

  • Literature review of current knowledge on steroid/triterpenoid biosynthesis and oxygen requirements.
  • Phylogenetic analysis of hopanoid and sterol biosynthetic pathways.
  • Experimental validation of sterol biosynthesis in cyanobacteria, including contamination controls.

Main Results:

  • Hopanoid biosynthesis is widespread in bacteria, with oxygen-dependent methylation in cyanobacteria.
  • Sterol biosynthesis is limited in bacteria and does not appear to occur in cyanobacteria, with evidence suggesting fungal contamination.
  • Sterol biosynthesis likely originated in the last common ancestor of eukaryotes, requiring significant oxygen (11 O2 molecules per cholesterol).

Conclusions:

  • The oxygen requirement for sterol biosynthesis makes an anaerobic evolutionary pathway unlikely.
  • Geological biomarker records (steranes, triterpanes) show conserved structures correlating with depositional environments.
  • Biomarkers are reliable environmental indicators, and understanding their biological roles enhances paleochemical interpretations.