Effect of low temperature on soybean peroxidase: spectroscopic characterization of the quantum-mechanically admixed spin state

A spectroscopic study of soybean peroxidase (SBP) has been carried out usin g electronic absorption, resonance Raman (RR) and electron paramagnetic res onance (EPR) spectroscopy in order to determine the effects of temperature on the heme spin state. Upon lowering the temperature a transition from hig h spin to low spin is induced in SEP resulting from conformational changes in the heme cavity, including a contraction of the heme core, the reorienta tion of the vinyl group in position 2 of the porphyrin macrocycle, and the binding of the distal His to the Fe atom. Moreover, the combined analysis o f the data derived from the different techniques at both room and low tempe ratures demonstrates that at low temperature the quantum-mechanically admir ed spin state (QS) of SEP has RR frequencies different from those observed for the QS species at room temperature. (C) 2000 Elsevier Science Inc. AII rights reserved.