The Digestive System and Nutrition

Amino Acids & Protein Structure

Coordination Chemistry

Glycolysis

Oxidative Phosphorylation

Important enzymatic processes that involve free radicals include the actions of superoxide dismutase and ribonucleotide reductase, as well as enzyme processes involving vitamin B12. The coenzyme, vitamin B12, is a really interesting case. B12 contains a coordinated cobalt atom. An unusual aspect is that one of the coordination positions is occupied by carbon, which is the only known carbon-metal bond in a biomolecule. This carbon metal bond is weak and is homeolytically cleaved to generate a methyl radical, which then abstracts a hydrogen atom as a prelude to intramolecular rearrangement, methylation, and reduction in certain biochemical transformations such as the addition of a carbon to the carbon skeleton of L-methylmalonyl CoA to form succinyl CoA, a portion of the pathway of the degradation of the amino acids methionine, isoleucine, and valine.