Insights into Sulfhemoglobin Detection: UV-Vis and Fluorescence Spectroscopy Correlations

The mechanisms by which drugs and several sulfur chemicals induce sulfhemoglobin formation have not yet been elucidated. However, enzymes producing hydrogen sulfide in mammalian tissues and organs suggest sulfhemoglobin and sulfmyoglobin formation mechanisms are more complex than previously hypothesized. The process involves the interaction of H₂S with hemoglobin or myoglobin in the presence of O₂ or H₂O₂ to generate sulfhemoglobin or sulfmyoglobin, respectively. Structurally, the sulfheme product chromophore is a covalent heme modification. This modification involves the incorporation of one sulfur atom within carbon atoms to form a sulfur-carbons ring moiety across the β-β double bond of heme pyrrole B, which shows a characteristic optical band around 623 nm and 618 nm for sulfhemoglobin and sulfmyoglobin, respectively. The results show a linear correlation between the sulfHb electronic charge transfer transition at 623 nm and the emission wavelength of 460 nm upon Soret excitation at 420 nm. The data show no such linear relationship for oxy-Hb or met-aquo Hb. This new approach allows us to measure from 0.02% to 13.5% sulfhemoglobin in mixtures of met-aquo hemoglobin and oxy-hemoglobin. Although additional work is needed, the results suggest that simultaneously monitoring sulfHb electronic transition at 623 nm and emission wavelength at 460 nm upon Soret excitation at 420 nm is a powerful technique to determine the percentage of sulfhemoglobin in blood. The data and techniques presented indicate that fluorescence spectroscopy coupled with UV-vis spectroscopy provides a fast and accurate method for detecting sulfhemoglobin in the blood, facilitating the diagnosis of sulfhemoglobinemia in patients.