Ultracentrifugation studies on the dissociation of chemically modified catalases

Abstract

The dissociation of a series of bovine catalases, in which a proportion of the carboxylic acid groups of glutamic and aspartic acids have been chemically modified by coupling with glycine methyl ester (GME) or ethylenediamine (ED), has been investigated by sedimentation rate and equilibrium methods. Sedimentation equilibrium measurements on GME derivatives have been analysed in terms of a monomer-dimer-trimer- tetramer model. The results show that the association of monomeric ( M 1) catalase subunits is consistent with the equilibria 4 M 1⇋2 M 2⇋ M 4. The Gibbs energies of association at 284K of the monomeric subunit to dimes ( M 2) and tetramers ( M 4) were found to be in the range − 28 to − 30 kJ mol −1 and − 91 to − 97 kJ mol −1, respectively. The Gibbs energy for association of dimer to tetramer is in the range − 32 to − 34 kJ mol −1. Chemical modification of bovine catalase markedly increases its susceptibility to dissociation by sodium n-dodecyl sulphate (SDS) and sedimentation rate measurements suggest that the initial event on addition of SDS is the dissociation of the whole molecule to half-molecules