Electrochemistry of chemically trapped dimeric and monomeric recombinant horseradish peroxidase

Native horseradish peroxidase (nHRP) exists in the aggregated form in concentrated water solutions as shown by dynamic light scattering (DLS). This is in contrast to recombinant horseradish peroxidase (recHRP) which mainly exists as a dimer. The native enzyme aggregates could be broken into the particles of nm-size only under the conditions of high ionic strength (0.5-1 M NaCl). Chemical cross-linking of recHRP with glutaraldehyde in water solutions yields 40% of the dimer. The chemically trapped dimeric and monomeric forms of recHRP were separated by gel-filtration, their substrate specificity towards a number of organic substrates compared. Parameters of direct and mediated electron transfer on graphite electrodes catalyzed by both preparations were analyzed. The difference in behavior of the monomeric and dimeric enzyme forms observed in electrochemical experiments was interpreted as a result of a “double” coverage of the electrode surface with the molecules of cross-linked dimeric enzyme, in contrast to both modified monomeric and original, unmodified recHRP providing “monolayer” coverage. In addition to the stabilization effects achieved due to enzyme surface modification with glutaraldehyde, the “double” coverage doubles the enzyme activity per surface unit