Kinetics of the hemerythrin-oxygen interaction.
The kinetics of the reaction of Golfingia gouldii hemerythrin with O2 have been studied by stopped flow spectrophotometry. For the second order oxygenation process, k1 = 7.4 X 10(6) M-1 s-1, deltaH1++ = 8.2 kcal-mol-1 and deltaS1++ = +1 e.u. at 25 degrees, pH 8.2, and I = 0.015 M. The rate constant is unchanged when protein concentration is varied from 3 to 25 muM, the ionic strength is increased to 0.07 M, and the pH moved to 6.8. The deoxygenation of oxyhemerythrin is studied with stopped flow by scavenging liberated O2 with S2O4(2-). For the first order dissociation, k-1 = 51 s-1, deltaH-1++ = 20.6 kcal-mol-1 and deltaS-1++ = +19 e.u. at 25 degrees, pH 8.2, and I = 0.015 M. The value of k-1 is independent of [protein] = 50 to 200 muM, [S2O4(2-)] = 5 to 100 mM I = 0.015 to 0.30 M and pH 6.8 to 9.0. Using myoglobin instead of S2O4(2-) as scavenger gives similar results. Combination of activation parameters for the oxygenation and deoxygenation processes gives K1 = 1.5 X 10(5) M-1, deltaH = -12.4 kcal-mol-1, and deltaS = -18 e.u., values in good agreement with independent thermodynamic data. Perchlorate ion (0.05 M) enhances k-1 about 3-fold and hardly effects k1. There is no sign of other than a single reaction in either direction, and octameric hemerythrin apparently behaves kinetically as eight single units.
D000818:Animals; D000845:Annelida; D001665:Binding Sites; D006422:Hemerythrin; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D008667:Metalloproteins; D010100:Oxygen; D011485:Protein Binding; D013696:Temperature; D013816:Thermodynamics
D006422:Hemerythrin; D008667:Metalloproteins; D010100:Oxygen