56] Determination of contents and redox states of ubiquinone and menaquinone

Abstract

This chapter determines the contents and redox states of ubiquinone (Q) and menaquinone (MK). The commercial availability of the dual-wavelength photometer was first designed by Chance. It is now possible to determine these quinones more sensitively and with greater accuracy and convenience. Investigation of the function of the quinones in mitochondria and bacteria has revealed that at least 95% of the quinones occur either in the oxidized (quinone) or reduced state (hydroquinone). A method for the determination of the content and the redox state of Q in animal tissue has also been described, whereas a method applicable to intact bacteria is lacking. Q is extracted with the redox state corresponding to the metabolic state of the preparation, whereas reduced MK is autoxidized during the extractions. As oxidized Q can be measured more accurately than reduced Q, it is advantageous to extract Q in the fully oxidized state for measuring its total content. The kinetics of the redox reactions of Q are measured directly using either the moving–mixing chamber or the flow apparatus designed by Chance.