Human serum albumin (HSA) is abundantly present in our blood and is a repository to many molecules, such as heme. Previous studies have confirmed that HSA reconstituted with heme (HSA-heme) imitates the binding site of other heme enzymes such as myoglobin (Mb), except that an O(tyrosine) bonds to the heme Fe center instead of a N(histidine). The aim of this project is to obtain imidazole complexes of HSA-heme, and then test for globin-like reactivities such as its ability to reduce nitrite to nitric oxide (otherwise known as nitrite reductase (NiR) activity). Adding imidazole, which mimics the structure of histidine, to HSA-heme generates a chemically-modified complex of the reconstituted protein that potentially forms an Fe-N(histidine)-like bond. This can be attained by complexing with a series of ligands: imidazole (Im), 1-methylimidazole (1-Im), and 2-methylimidazole (2-Im). Current results show unique spectral features associated with the Fe(II) and Fe(III) forms of the chemically-modified HSA-heme, specifically when complexed with 1-Im. Addition of nitric oxide to the HSA-heme1-Im generates distinctive spectral bands comparable to the product created when this complex is allowed to react with nitrite, confirming NiR activity. Further tests will be done to determine the rate constants of the reaction between the HSA-hemeimidazole complexes and nitrite. This work allows us to understand the effect of the heme proximal ligand on the nitrite reductase activity of chemically-modified heme proteins.

Constructing imidazole complexes of human serum albumin reconstituted with heme and testing for globin-like reactivities

255th National Meeting (2018)

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