Nonenzymatic hydroxylations of proline and lysine by reduced oxygen derivatives

Abstract

The biosynthesis of trans-3- and trans-4-hydroxyprolines and 5-hydroxylysine in animal cells requires polypeptide proline or lysine, enzymes and cofactors including iron, and possibly involves peroxidatic intermediates¹. Several laboratories have reported the presence of low-molecular-weight hydroxyproline and hydroxylysine peptides in cell and organ cultures^2–5. We found that these small peptides contained the trans-3 and cis-4 isomers of hydroxyproline as well as trans-4 ones and that their production was not completely inhibited by α, α-dipyridyl, an iron chelator and effective inhibitor of enzyme-mediated hydroxylations⁵. It is known that oxygen or hydrogen peroxide in the presence of metal can hydroxylate proline and other aromatic compounds^6–11. We show here that reduced oxygen derivatives can hydroxylate both free and poly peptide-bound proline and lysine, and that scavengers of hydroxyl radicals suppress, but do not completely inhibit, this reaction. Reduced oxygen derivatives can be generated in normal and pathological circumstances¹², and some of the low-molecular-weight hydroxyproline and hydroxylysine peptides found in cell and organ cultures might be derived from these derivatives and therefore do not reflect collagen turnover, but rather some other cellular activity.