Figure 6.

Illustration of the cofactor role of SCN⁻ or I⁻. When the necessary conditions are fulfilled, that is, (i) no substrate competitor for SCN⁻ or I⁻ for binding to lactoperoxidase, (ii) enough peroxidase, H₂O₂ and SCN⁻ or I⁻, (iii) enough R-SH, and (iv) no incorporation of SCN⁻ or I⁻ in stable byproducts, the quantity of OSCN⁻ or OI⁻ produced depends only on the amount of H₂O₂. SCN⁻: thiocyanate; I⁻: iodide; H₂O₂: hydrogen peroxide; LPO: lactoperoxidase; R-SH: peptide or protein with a thiol moiety; R-S-SCN or R-S-I sulfenyl thiocyanate or iodide; R-SOH: sulfenic acid; OSCN⁻: hypothiocyanite; and OI⁻: hypoiodite.