title: Activation volumes for horseradish peroxidase compound II reactions.
abstract: The activation volumes for the reactions of horseradish peroxidase compound II with L-tyrosine, 3-iodo-L-tyrosine, p-aminobenzoic acid and ferrocyanide were determined by using a high-pressure stopped-flow technique at 25 degrees C and pH 7. For the tyrosines, the solvent electrostriction accompanying substrate ionization and H+ transfer from the substituted phenol to a basic group of the enzyme can account for the observed negative activation volumes. For p-aminobenzoic acid a simple electron transfer without H+ transfer appears to occur. The positive activation volume for ferrocyanide may be explained in terms of electron transfer associated with a large change in electrostriction of the inorganic redox couple.
mesh_terms: D004789:Enzyme Activation; D006735:Horseradish Peroxidase / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D010544:Peroxidases / Q000378:metabolism*; D011312:Pressure
chemical_list: D046911:Macromolecular Substances; D006735:Horseradish Peroxidase; D010544:Peroxidases