Kinetics and thermodynamics of the reaction of deoxyhemerythrin with nitric oxide.
Deoxyhemerythrin reacts with NO to form a 1:1 adduct shown spectrophotometrically. The kinetics of the formation have been studied directly by stopped-flow measurements at four different temperatures (0.0-23.6 degrees C). The kinetics of the dissociation have been studied, also by stopped-flow techniques, at five different temperatures (4.0-35.1 degrees C) using three different scavengers [Fe(II)(edta)2-, O2 and sperm whale deoxymyoglobin], which gave similar values. For the formation kf = (4.2 +/- 0.2) x 10(6) M-1 s-1, delta Hf not equal = 44.3 +/- 2.3 kJ mol-1, delta Sf not equal to = 30 +/- 8 J mol-1 K-1 and for the dissociation kd = 0.84 +/- 0.02 s-1, delta Hd not equal to 95.6 +/- 2.1 kJ mol-1 delta Sd not equal to = 74 +/- 7 J mol-1 K-1 (25 degrees C, I = 0.2 M and pH 7-8.1). From the kinetic data the thermodynamic data for the formation of HrNO were calculated: Kf = (5.0 +/- 0.3) x 10(6) M-1, delta H = -51.3 +/- 3.1 kJ mol-1 and delta S = -44 +/- 11 J mol-1 K-1 (25 degrees C). The kinetic data suggest that NO occupies the same iron(II) site in deoxyhemerythrin as oxygen does. The equilibrium constant for the formation of Fe(II)(edta)(NO)2- has been redetermined: K1 = (1.45 +/- 0.07) x 10(7) M-1, delta H = -77.5 +/- 1.5 kJ and mol-1 and delta S = -123.5 J mol-1 K-1 (25 degrees C).
Springborg
J
J
Chemistry Department, Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
Wilkins
P C
PC
Wilkins
R G
RG
D001711:Biotransformation; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004492:Edetic Acid; D006422:Hemerythrin / Q000031:analogs & derivatives* / Q000737:chemistry; D008970:Molecular Weight; D009211:Myoglobin / Q000032:analysis; D009569:Nitric Oxide / Q000737:chemistry*; D013816:Thermodynamics
D006422:Hemerythrin; D009211:Myoglobin; C043119:deoxyhemerythrin; D009569:Nitric Oxide; D004492:Edetic Acid