Microscopic ligand binding rates for GLB-26 and electron transfer rates to Cyt-c and O2 compared to Ngb, Cygb, and Mb.

Experimental conditions: 50 mM potassium phosphate buffer 0.1 mM EDTA pH 7.0, 25°C.*from [30] and for human Ngb after reduction of the intra-disulfide bond.§Data partially published from [25]. ⊥Data from [38] for human Cygb after reduction of the intra-disulfide bond. £Measurement for Sperm Whale recombinant Mb in presence of 5 U/ml of catalase and SOD. °The O2 solubility coefficient was taken as 1.82 µM/torr. Note the distinction between the intrinsic affinity KO2 = koff/kon (as for pentacoordinated forms) and the overall affinity for the ligand competition of the hexacoordinated globins obtained from the ratio of KO2 and KHis (koff/kon)/(1+KHis)) and used here for the P50O2 calculation. $these values are measured under air (35% O2 for GLB-26) and represents the lower limit of the autoxidation rate at 37°C; the rate increased at O2 tensions closer to the P50O2 for which the bimolecular oxidation of the hexacoordinated form by O2 prevails. A value of 0.8/s close to that of GLB-26 was measured for GLB-6 another hexacoodinated globin under air (21% O2) [26].