Abstract
The reduction of metmyoglobin by the iron(II)complex of ira/«-l,2-diaminocyclohexane-./V,./V,7V',7V,-tetra-acetate (FeCDTA2-) has been investigated. The equilibri-um constant, measured spectrophotometrically, is 0.21 witha resulting reduction potential of 0.050 V for Mb0. The rateconstant for the reduction is 28 M-1 sec-1 with a AH* of13 kcal M~x and AS* of -11 eu. Both CN- and OH- in-hibit the reduction because of the relatively low reactivity ofcyanometmyoglobin (Mb+CN-) and ionized metmyoglobin(Mb+OH-). The rate constant for the reduction ofMb+CN- by FeCDTA2- is 4.0 X 10-2 M-1 sec-1 and that for reduction of Mb+OH- is 4.8 M-1 sec-1. The nitricoxide complex of metmyoglobin is reduced with a rate con-stant of 10 M~x sec-1. The kinetics of oxidation of oxymyo-globin by FeCDTA- were studied. The data are consistentwith a mechanism where oxidation takes place entirelythrough the deoxy form. A rate constant of 1.45 X 102 M~xsec-1 was calculated for the oxidation of deoxymyoglobinby FeCDTA-, in excellent agreement with that calculatedfrom the equilibrium constant and rate constant for reduc-tion. The above data are discussed in terms of a simpleouter-sphere reduction reaction.