The Reduction Potential of Lactoperoxidase.

Abstract
The reduction potential of Fe(III)/Fe(II) lactoperoxidase [from cow''s milk] was determined. Optical determinations of equilibria with 2-methyl-3-hydroxy-1,4-naphthoquinone as indicator and prereduced 9,10-anthraquinone-2-sulfonate as reducing agent gave Em.7.0 = -191 .+-. 2 mV. Potentiometric determinations with 9,10-anthraquinone-2-sulfonate as mediator and, in the reduced form as reducing agent, gave Em.7.0 = -188 .+-. 1 mV. Addition of 0.5% N-cetyl-N,N,N-trimethylammonium bromide, and using dithionite as reducing agent, gave Em.7.0 = -183 mV and -179 mV with 9,10-anthraquinone-2-sulfonate and 9,10-anthraquinone-2,6-disulfonate, respectively, as mediators.

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