Peer-reviewed evidence
What the 2015 PNAS study showed
Zhang and colleagues studied mice carrying a βCys93Ala hemoglobin mutation. The mutation did not remove hemoglobin's basic oxygen-carrying function, but it impaired hypoxic vasodilation, reduced peripheral blood flow and tissue oxygenation, and was associated with myocardial ischemia and worse adaptation to transient hypoxia.
The authors interpreted βCys93-derived S-nitrosothiol bioactivity as an important component of red-cell-mediated regulation of blood flow and tissue oxygenation.
Reference: Zhang R, Hess DT, Qian Z, et al. Hemoglobin βCys93 is essential for cardiovascular function and integrated response to hypoxia. PNAS. 2015;112(20):6425-6430. DOI: 10.1073/pnas.1502285112.