Oximetry with the NMR signals of hemoglobin Val E11 and Tyr C7

The NMR visibility of the signals from erythrocyte hemoglobin (Hb) presents an opportunity to assess the vascular PO2 (partial pressure of oxygen) in vivo to gather insight into the regulation of O2 transport, especially in contracting muscle tissue. Some concerns, however, have arisen about the validity of using the Val E11 signal as an indicator of PO2, since its intensity depends on tertiary structural changes, in contrast to the quaternary structure changes associated with relaxed (R) and tense (T) transition during O2 binding. We have examined the Val E11 and Tyr C7 signal intensity as a function of Hb saturation by developing an oximetry system, which permits the comparative analysis of the NMR and spectrophotometric measurements. The spectrophotometric assay defines the Hb saturation level at a given PO2 and yields standard oxygen-binding curves. Under defined PO2 and Hb saturation values, the NMR measurements have determined that the Val E11 signal, as well as the Tyr C7 signal, tracks closely Hb saturation and can therefore serve as a vascular oxygen biomarker.