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 a 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 Å 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.