NMR studies of hemoproteins: pH dependence of ferric horseradish peroxidase and horse heart myoglobin

Abstract

N.m.r. spectroscopy has recently developed into a powerful tool for investigating structure and structurefunction relationships of hemo-proteins and heme enzymes. Most of the n.m.r. studies on ferric hemoproteins so far reported have been performed with those in purely or nearly low spin state. Several of the ferric hemoproteins, which exhibit a pHdependent spin state change, have been incompletely investigated [ 1,2] . In this report we concentrate on the n.m.r. measurements of pH-dependence for ferric horseradish peroxidase and horse heart myoglobin, covering the large hyperfine shift of heme ring methyl groups due to ferric high spin state. 220 MHz proton n.m.r. confirmed the result of magnetic susceptibility measurements by Theorell and Ehrenberg [3], and was, furthermore, able to distinguish the nature of the pH dependent spin state change between both hemoproteins.