Relative roles of heme-irons and globin-thiols in the genesis of acellular hemoglobin mediated vasoconstriction.

Abstract:In addition to heme-irons, reactive (β-globin thiols (βCys93s) of hemoglobin (Hb) also have been shown to interact with endogenous nitric oxide (NO) thereby contributing to vascular tone regulation. What relative roles do these NO binding sites contribute to the overall Hb-mediated vasoactivity? Several test Hbs with either or both the NO binding sites preliganded or blocked were prepared and tested in a rat thoracic aortic ring model. Hbs tested were: NEM-Hb (ferrous Hb with masked thiols), HbNO (ferrous Hb preliganded with NO), Hb+CN (ferric Hb liganded with CN−), NEM-HbNO and NEM-Hb+CN (Hbs with both heme-iron and cysteine sites preliganded or blocked). Typically, >0.2 μM control Hb significantly increased isometric tension in agonist stimulated vessel rings (58.1 ±7.0% over baseline). At comparable concentrations, NEM-Hb also caused a significant contraction (50.7±9.5%) while HbNO and Hb+CN did not (−5.5±6.0% and −3.7±4.6%, respectively). For these Hbs, masking thiols as well did not signific...