Abstract
AbstractRecent studies of Cu, Zn superoxide dismutase, and of zinc‐finger peptides have established that histidine ligands can be detected in ultraviolet resonance Raman (UVRR) spectra, following NH/D exchange of the imidazole. UVRR spectroscopy therefore offers promise for monitoring histidine ligation in heme proteins. In this work, we characterize heme‐bound histidine UVRR bands for N‐acetyl‐microperoxidase‐8 (MP‐8) and microperoxidase‐11 (MP‐11), and also for hemoglobin (Hb). The Hb UVRR spectra are dominated by tyrosine and tryptophan contributions, but a band appears at 1340 cm−1 in D2O solution, which is assigned to a mode of Fe‐bound imidazole. This band shifted 24 cm−1 in protein which was labeled with 15N via expression of the Hb gene in E. coli grown on 15NH4+. In MP‐11, the position of this band is insensitive to ligation or oxidation state changes, but it is 2 cm−1 lower in deoxyHb than in the CO adduct. This shift may reflect mechanical forces on the proximal histidine in the T state, and/or changes in its H‐bonding.
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