Enzymatic radioiodination of phospholipids catalyzed by lactoperoxidase

Phospholipids were iodinated with iodide by a lactoperoxidase-catalyzed reaction in the presence of controlled amounts of H₂O₂ which were continuously supplied by glucose oxidase + glucose. Different molecular and ionic species of inorganic iodine present in the reaction mixture (i.e., I^?, I₂, I₃^?) were eliminated by thiosulfate reduction to I^? followed by gel filtration on Sephadex LH-20 which separated I^? from the phospholipids completely. Final separation and identification of individual phospholipids were done on a column of silica gel H using a single solvent mixture consisting of CHCl₃:CH₃OH:CH₃COOH:H₂O (25:15:4:2, by volume). Application of phospholipases A₂ and D or transesterification provided evidence to indicate a covalent iodination of the fatty acid moiety of the lipids by the enzymatic process, which apparently is substitution but could also proceed by addition to the double bonds, when present.