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Related Concept Videos

Radicals01:27

Radicals

Roots, often written as radicals, identify the quantity that must be raised to a specific exponent to produce a given value. A radical expression consists of two main components: the radicand, which is the value placed inside the root symbol, and the index, which indicates the degree of the root being taken. The notation n√a indicates the principal nth root of a. If n equals 2, the operation is the square root, while n = 3 defines the cube root. When n is even, a negative radicand does not...
Radical Reactivity: Overview01:11

Radical Reactivity: Overview

Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Radical Formation: Addition00:47

Radical Formation: Addition

Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Radical Formation: Overview01:03

Radical Formation: Overview

A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the latter, also known...
Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a low‐energy SOMO, which interacts...
Radical Formation: Abstraction00:47

Radical Formation: Abstraction

The electron of an atom can be abstracted from a compound by a relatively unstable radical to generate a new radical of relatively greater stability. For example, an initiator which forms radicals by homolysis can abstract a suitable species like a hydrogen atom or a halogen atom from a compound to generate a new radical. This ability of radicals to propagate by abstraction is a crucial feature of radical chain reactions.
Even though homolysis produces radicals, it is different from radical...

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Related Experiment Video

Updated: Jul 7, 2026

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow
10:34

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

Published on: April 24, 2014

The Radical SAM Superfamily.

Perry A Frey1, Adrian D Hegeman, Frank J Ruzicka

  • 1Department of Biochemistry, University of Madison, Wisconin-Madison, Wisconsin 53726, USA. frey@biochem.wisc.edu

Critical Reviews in Biochemistry and Molecular Biology
|March 1, 2008
PubMed
Summary

Radical S-adenosylmethionine (SAM) enzymes utilize a [4Fe-4S] cluster to bind SAM, initiating over 40 biochemical transformations. Most of these 2800+ proteins remain uncharacterized, but studied members share a common radical mechanism.

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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
14:22

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

Published on: April 15, 2013

Area of Science:

  • Biochemistry
  • Enzymology
  • Structural Biology

Background:

  • The radical S-adenosylmethionine (SAM) superfamily contains over 2800 proteins characterized by a CxxxCxxC motif.
  • This motif coordinates a [4Fe-4S] cluster essential for binding SAM and facilitating diverse biochemical reactions.
  • While many radical SAM enzymes are uncharacterized, a few have been studied in detail.

Purpose of the Study:

  • To review the known biochemical and structural information of characterized radical SAM enzymes.
  • To highlight the common mechanistic features of this enzyme superfamily.
  • To underscore the vast potential for future research into uncharacterized members.

Main Methods:

  • Literature review of existing biochemical and structural studies on radical SAM enzymes.
  • Comparative analysis of characterized enzymes to identify conserved features.
  • Focus on mechanistic insights derived from studies of specific enzymes like lysine 2,3-aminomutase and pyruvate formate-lyase.

Main Results:

  • Radical SAM enzymes employ a conserved mechanism involving the cleavage of the [4Fe-4S](1+) -SAM complex.
  • This cleavage generates a 5'-deoxyadenosyl radical, which abstracts a hydrogen atom from the substrate to initiate radical-based transformations.
  • Detailed mechanistic and structural data exist for a limited number of enzymes, including MoaA and lipoyl synthase.

Conclusions:

  • The radical SAM superfamily is a large and functionally diverse group of enzymes.
  • A conserved radical initiation mechanism is central to the activity of characterized members.
  • Further biochemical and structural characterization of unstudied radical SAM enzymes is warranted to explore their full functional potential.