Femtosecond spectroscopy studies of recombinant hemoglobin I of the clam Lucina pectinata (Gmelin, 1791)

Abstract

Lucina pectinata (Gmelin, 1791) is a clam that can be found in sulfide-rich muds in the coastal mangroves of the southwest coast of Puerto Rico. It contains three different hemoglobins in the gill tissue, hemoglobin I, II and III (HbI, HbII and HbIII, respectively), each one characterized by distinct physical-chemical properties. Hemoglobin I (HbI) is a monomeric protein of 142 amino acid residues, and it is responsible for oxygen and/or hydrogen sulfide transportation. These proteins present an excellent scenario for the study of dynamics of their reaction with diatomic small molecules and H2S. With the development of a state-of-the-art ultrafast laser system and experimental setup we were able to study the initial steps in the reaction of HbI and HbI mutants in various electronic states with its native ligand (H2S) in the fs to ps time regime. The HbI-H2S kinetics showed a second component of ~12ps, two times faster than the same component for the metaquo specie. Furthermore the transient absorption spectra do not show the classical ligated to unligated trace indicating the presence of at least three different species during the initial photolysis steps. It has been observed that in the presence of H2S HbI can undergo reduction from its FeIII state, the mechanism is still unknown but our experiments demonstrate that this could be feasible. Measurements taken for the rHbI ferrous complex, demonstrated that small fraction of photo-oxidation of the sample occurred.