OxyFile #150

Reactive oxygen species in living systems: source, biochemistry, 
and role in human disease.
Barry Halliwell
American Journal of Medicine 
Sept 30, 1991 v91 n3C p14S(9) 
Author's Abstract 
Reactive oxygen species are constantly formed in the human body 
and  removed by antioxidant defenses. An antioxidant is a 
substance that, when present at low concentrations compared to 
that of an oxidizable substrate, significantly delays or prevents 
oxidation of that substrate. Antioxidants can act by scavenging 
biologically important reactive oxygenspecies 
([O.sub.2].,[H.sub.2][O.sub.2], .OH, HOCl, ferryl, peroxyl, and 
alkoxyl), by preventing their formation, or by repairing the 
damage that  they  do.  One  problem  with scavenging-type 
antioxidants is that secondary radicals derived from them can 
often themselves do biologic damage. These various principles 
will be illustrated by considering several thiol compounds.