Gradient PAGE (4–15%) of paramagnetic substrates and reaction mixtures with peroxidases and glucose oxidase (silver stain). Reactions were carried out in 5mM D-glucose, DPBS, pH 6.8. Substrates were at 0.5 mM. Lanes: 1 – reaction mixture of HRP and GOX, no substrate; lane 2 – reaction mixture of MPO and GOX, no substrate; 3 – substrate I (20 μl); 4 – reaction mixture of HRP and GOX, substrate I; 5 – reaction mixture of MPO and GOX, substrate I; 6 – substrate II (20 μl); 7 – reaction mixture of HRP and GOX, substrate II; 8 – reaction mixture of MPO and GOX, substrate II. Cross-linked product is marked with an arrow.