Oxidation-Reduction Potentials of Heme a Hemochromes
Garret Vanderkooi 1 and Elmer Stotz 1
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1 From the Department of Biochemistry, The University of Rochester School of Medicine and Dentistry, Rochester, New York 14620
An apparatus is described in which it is possible to measure the oxidation-reduction potential and to follow the absorption spectrum on the same solution. A method is also described by which the dependence of the midpoint potential of a system on pH can be determined by titrating a buffered, partially reduced solution with alkali. Oxidation-reduction studies were performed on the pyridine, histidine, and imidazole hemochromes of heme a. A new species of the imidazole hemochrome of heme a was discovered; it has absorption bands at 456 and 610 mµ it is related to the "strongly interacting" imidazole hemochrome described in a previous paper (2) which has bands at 456 and 596 mµ under the conditions used here. The midpoint potentials found for the various hemochromes at pH 7.0 are: pyridine, +0.278 volt; histidine, -0.056 volt; histidine plus sodium dodecyl sulfate, -0.041 volt; strongly interacting imidazole hemochrome with bands at 456 and 596 mµ, +0.045 volt; strongly interacting imidazole hemochrome with bands at 456 and 610 mµ, +0.079 volt; sodium dodecyl sulfate added to the strongly interacting imidazole hemochrome, -0.038 volt. Structural interpretations are given insofar as possible to account for the potential versus pH data. The relationship of this work to cytochrome oxidase is discussed.
Submitted on February 17, 1966
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