Serum albumin (SA) is the most abundant protein in the circulatory system that functions as a repository for a host of molecules, including heme b (iron protoporphyrin IX). The crystal structure of the complex derived from humans, HSA-heme, shows heme binding in subdomain IB with several amino acids stabilizing the co-factor within the protein matrix. The residues are Tyr138, Tyr161, Ile142, His146, and Lys190. The complex itself resembles the active site of other heme enzymes such as catalase and globins (e.g. hemoglobin, Hb and myoglobin, Mb), which scavenge reactive nitrogen species (RNS) or transport oxygen, respectively. One of the goals of this work is to elucidate whether evolution retained these key amino acids, or if it added new variance to accommodate species-specific problems. Several of the species investigated in this work have various behavioral tendencies such as diving, migration, and hibernation, and we seek to determine the role of SA in heme binding and oxidative stress response in light of current literature. Cross-species analyses were carried out using Clustal Omega multiple sequence alignment of the key residues, while the potential for oxidative stress response via RNS reactions is investigated using absorption spectroscopy. Results demonstrate that the region of heme binding is fairly conserved throughout the species studied, at least in the properties of the amino acids, implying retention of function for heme coordination within the subdomain. Absorption spectroscopy establishes RNS (e.g. nitric oxide) binding to HSA-heme, alluding to the complex’s influence on oxidative stress correction.
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