Molecular engineering and polyethylene glycol modification of hemoproteins: conversion of myoglobin into peroxygenase

Mvoglobin (Mb) normally functions as a carrier fur mole<iilar oxygen, but it catalyses hydrogen peroxide supported one- and two-electron oxidation of a variety of substrate-.. Although the catalytic intermediate for these reaction.-, luve not been < learlv idem ilied. cMalysi.s appears to be associated with a ferry! radical cation specie-, equivalent to compound I of peroxidases. However, t lie turnover numbers tor oxidative PM lions by Mb are less than the values for peroxidases. Thus, we have compared X-ray crystal structures of c.ytochrome c peroxidase and Mb. and constructed the L2IHI/H64L and F-KIH/Hfi-H, Mb to mimic the active- site uf peroxidase. '1'hp Vmax values for the one electron oxidation by the mutants differ by little from the corresponding values lor the wild type Mb. but 1.2011 /Hfi-l I, Mb catalyses the two-electron oxidation of thioethers and styrène into the oxygenated products at least 1Ü times as fast as the recombinanl wild tvpe. with higher enanVioselectivity. Furthermore-, 1 he more than 100 fold enhancement in the rate versus the wild type is observed for F43 F4-JH/H64l. cataly/ed oxygénation. More Jnt riguingly. we have identified compound I like species if F-l-iH /Hti4l, mutant as the catalytic intermediate for the first time. Our result n clear!) indicate that the alignment of the distal histidine is import an! for the reactivity of Mb. For further characterization of 1 he (ransient inter mediate, the polyethylene glycol modification of Mb would be a promising approach as we previously stabili/ed compound I of the modified horseradish peroxnlae in organic media at 20 degrees.