NUCLEOSIDE TRIPHOSPHATE LEVELS VERSUS OXYGEN-AFFINITY OF RATTLESNAKE RED-CELLS

Squamate hemoglobins are responsive to modulation by nucleoside tripho sphates (NTP, generally ATP), and bind NTP with a 1-to-1 molar stoichi ometry. However, red cells of nonpregnant rattlesnakes contain NTP-to- hemoglobin molar ratios of similar to 2.5 suggesting most NTP is super saturating and should not influence the oxygen affinity directly. To t est this hypothesis, we metabolically depleted red cells of NTP and de termined the oxygen affinity. There was a significant linear relations hip between red cell NTP concentrations and oxygen affinity over the N TP/Hb range examined. In contrast, intracellular pH, Mg2+ and Cl- chan ged slightly, or not at all, during depletion. These data indicate NTP concentrations represent the primary control of hemoglobin function w ithin these cells. Purified hemoglobin was functionally sensitive to 5 mM GTP or inositol hexaphosphate but not sensitive to 5 mM ATP or pH. Together, these findings indicate rattlesnake hemoglobin, within red cells, is functionally controlled by NTP, but the binding affinity is low such that NTP is not saturating at NTP/Hb ratios below 3.5.