Absence of ligand binding-induced tertiary changes in the multimeric earthworm Lumbricus terrestris hemoglobin. A...

In vertebrate hemoglobins, changes in protein tertiary structure induced by either ligand binding or changes in quaternary state are manifested at the heme as reflected in resonance Raman spectral changes involving the iron-proximal histidine stretching mode. No such changes are observed for Lumbricus terrestris hemoglobin. The iron-histidine stretching mode and the porphyrin breathing motion in the deoxy-, oxy-, or CO-photodissociated forms of Lumbricus hemoglobin and human hemoglobin A (pH 7.0 and 9.2, the latter to effect Lumbricus hemoglobin subunit dissociation) were studied using pulsed (10 ns) light at 435 nm. In contrast to that observed for hemoglobin A, a comparison of the spectra of the deoxy and photoproduct forms of Lumbricus hemoglobin reveal minimal differences in the region of the iron-histidine and the pi electron distribution in the heme moiety. The spectral frequencies are similar to that observed in R-state vertebrate hemoglobins. Such average behavior of the approximately 192 hemes present in Lumbricus hemoglobin is more analogous to the Raman spectral properties observed in myoglobin.