NMR VISIBILITY STUDIES OF N-DELTA PROTON OF PROXIMAL HISTIDINE IN DEOXYHEMOGLOBIN IN LYSED AND INTACT RED-CELLS

Recent in vivo H-1 MRS studies of muscle oxygen levels by means of myoglobin (Mb) oxygenation have necessitated an investigation of the possible contamination from deoxy-hemoglobin (Hb). To determine the contribution of Hb in these NMR measurements, we studied the NMR visibility of histidyl N-delta proton of Hb in lysed and intact RBC (red blood cell) suspensions. We found that the visibility of deoxy-Hb was significantly lower in intact RBCs (ca. 16%) than the solution form at an equivalent concentration of beta home-iron, even though the visibility of deoxy-Hb from lysed RBC and deoxy-Mb was almost identical. Our study also shows that visibility increases with RBC swelling. Based on the difference in concentration and compartmentation, we conclude that less than 17%. contribution from Hb is expected in Mb measurements in vivo. The possible mechanisms which cause the low visibility of Hb in RBCs are discussed.