High resolution proton nuclear magnetic resonance spectroscopy of lactoperoxidase

The first high resolution proton nuclear magnetic resonance spectra are reported for the native ferric and ferric cyano complexes of bovine lactoperoxidase. The spectrum of the native species exhibits broad heme signals in a far downfield region characteristic of the high-spin ferric state. The low-spin cyano complex yields a proton nuclear magnetic resonance spectrum with signals as far as 68.5 ppm downfield and as far as -28 ppm upfield of the tetramethylsilane reference. These peak positions are anomalous with respect to those seen only as far as 35 ppm downfield in other cyano hemoprotein complexes. An extreme asymmetry in the unpaired spin delocalization pattern of the iron porphyrin is suggested. The unusual proton nuclear magnetic resonance properties parallel distinctive optical spectral properties and the exceptional resistance to heme displacement from the enzyme. Lactoperoxidase utilized in these studies was isolated from raw milk and purified by an improved, rapid chromatographic procedure.