Lactoperoxidase (LPO) is a glycoprotein with a hemin prosthetic group which may occur as a mixture of two isozymes. It has a molecular weight of 77,500 daltons. LPO catalyzes the hydrogen peroxide oxidation of iodide according to the following reaction:
2I- + H2O2 + 2H+ → I2 + 2H2O.
Iodide reacts directly with the heme group; upon addition of H2O2 the complex iodinates the substrate. LPO is inhibited by hydrazines. The assay procedure has been updated from that of Morrison to an ABTS®/H2O2 based method with increased sensitivity and reproducibility.