Characterization and Solubilization of the Alternative Oxidase of Sauromatum guttatum Mitochondria

Abstract

The alternative oxidase activity of Sauromatum guttatum spadix mitochondria has been investigated as to its developmental expression and tissue localization. Mitochondria rich in alternative oxidase activity were found in a yellow cortex tissue present to varying degrees within the appendix, male floral, and sterile floral regions of the spadix. During a 5-day period just prior to anthesis, the alternative oxidase activity present in the appendix region was found to increase over 10-fold. On the following day when the appendix region becomes thermogenic, cytochrome oxidase activity was found to decrease by 92%, effectively forcing electron flow through the alternative oxidase. A procedure for efficient solubilization of the alternative oxidase from appendix region mitochondria was developed. The alternative oxidase thus solubilized was sensitive to heat inactivation and trypsin digestion. The activity showed inhibition characteristics expected of the alternative oxidase in that it was sensitive to salicylhydroxamic acid and 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole, but relatively insensitive to KCN and antimycin A. Essential sulfhydryl group(s) were indicated by reversible inhibition by p-chloromercuribenzoic acid. The solubilized alternative oxidase was most active in the detergent N,N-bis-(3-d-glucoamidopropyl)-deoxycholamide and had a pH optimum of 6.8.