Protoheme conformations in low-spin ferrohemoproteins. Resonance Raman spectroscopy.

The low-frequency regions of resonance Raman spectra of various low-spin ferrous forms of normal human hemoglobin, soybean leghemoglobin alpha and of horse myoglobin are reported. Differences observed among the spectra of oxygenated and nitrosyl forms of these hemoproteins show that their globins impose various low-spin heme structures. A quantitative correlation between the variable frequency of resonance Raman band II (215-271 cm-1) and the iron atom-heme plane distance was observed for hemoproteins and heme models, either ferrous or ferric, high-spin or low-spin. From this correlation, the iron atom-heme plane distance should be 0.3 A in nitrosyl and oxymyoglobin (band II at 256 cm-1) whereas the iron position should be near to or in the heme plane for nitrosyl and oxy forms of hemoglobin and leghemoglobin (band II between 266 and 273 cm-1). A new method is proposed for monitoring the photodissociation processes in ferrohemoproteins.