Several hemoglobins were explored by UV-Vis and resonance Raman spectroscopy to define sulfheme complex formation. Evaluation of these proteins upon the reaction with H2O2 or O-2 in the presence of H2S suggest: (a) the formation of the sulfheme derivate requires a HisE7 residue in the heme distal site with an adequate orientation to form an active ternary complex; (b) that the ternary complex intermediate involves the HisE7, the peroxo or ferryl species, and the H2S molecule. This moiety precedes and triggers the sulfheme formation. (C) 2010 Elsevier Inc. All rights reserved.