Simultaneous observation of the O-O and Fe-O-2 stretching modes in oxyhemoglobins

Understanding of the chemical nature of the dioxygen moiety of oxyhemoglobi n is crucial for elucidation of its physiological function. In the present work, direct Raman spectroscopic observation of both the Fe-O-2 and O-O str etching modes unambiguously establishes the vibrational characteristics of the oxygen-bound heme moiety in the hemoglobins of Chlamydomonas eugametos and Synechocystis PCC6803. In addition to providing the resonance Raman ass ignment of the O-O stretching mode (1136 cm(-l) for Chlamydomonas, 1133 cm( -1) for Synechocystis) in an oxyhemoglobin with an iron-porphyrin, this stu dy also reports unusually low frequencies for the Fe-O-2 stretching modes ( 554 cm(-l)). The effect of strong hydrogen bonding to the bound oxygen is c onfirmed by changes in the frequency of the Fe-O-2 stretching mode on mutat ion of distal residues, These findings suggest an enzymatic function rather than an oxygen transport role for these hemoglobins.