Horseradish peroxidase catalytic residues

Ugarova NN, Rozhkova GD, Berezin IV (1979) Chemical modification of the e-amino groups of lysine residues in horseradish peroxidase and its effect on the catalytic properties and thermostability of the enzyme. Biochim Biophys Acta 570 31 12... 

The integrity of the heme group after decay of CIII may be corroborated by different methods, including residual catalytic activity or spectroscopic methods. It has been reported that the decay product of horseradish peroxidase CIII presents a diminished intensity of the Soret band (proportional to the loss of peroxidasic activity) and the appearance of a new signal at 670 nm. This compound was named p670 and has been explained as the accumulation of verdoheme [53, 107]. 

Electrode processes in experiments with redox indicators involved one or a few electrons and were, therefore, inherently low-yield reactions. Recently catalytic processes have been used to collect as many electrons as possible ([327, 454, 455] E. Palecek, M. Fojta, and L. Havran, unpublished). Thorp [327] used a soluble mediator that moved close to G residues present only in target DNA (but absent in the probe) and shuttled electrons to the polymer-modified ITO electrode. The reduced form of the mediator [Ru(bipy)3] + was oxidized by holding the electrode at a sufficiently positive potential. The oxidized form of the mediator removed electrons from G residues, generating reduced [Ru(bipy)3] + and completing a catalytic cycle. About 100 electrons per hybridized G could be collected under favorable conditions. Horseradish peroxidase coupled to target DNA was applied to detect the hybridization by electrocatalytic reduction of hydrogen peroxide... 

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