Isuke Imada

Effects of idebenone and related compounds on respiratory activities of brain mitochondria, and on lipid peroxidation of their membranes

The oxidation of succinate and NADH in a ubiquinone-depleted canine brain mitochondrial preparation was restored by a low molecular weight benzoquinone, idebenone. Idebenone inhibited NADH(NADPH)/ADP-Fe3+-dependent lipid peroxidation in canine brain mitochondria and protected against the resulting inactivation of NADH-cytochrome c reductase activity. Idebenone did not affect the activities of succinate oxidase in canine and rat brain mitochondria but suppressed the oxygen consumption in NADH oxidation. This suppression might be related to the inhibition of lipid peroxidation. These results suggest that idebenone functions as an electron carrier in the respiratory chains of brain mitochondria and as an antioxidant against membrane damage caused by lipid peroxidation in brain mitochondria.

Ubiquinone and related compounds. XXI. Determination of ubiquinone-10 in human blood.

Abstract UQ-10 in human blood could be determined by electron capture gas chromatography. In this chromatography, a part of UQ-10 was cyclized to UC-9 and the latter was twice as sensitive as the former. Chromanol compounds involving perhydroubichromanol-9 and α-tocopherol were similarly determined. It was made clear by this method that UQ-10 in human blood is present mainly in the serum, and the mean value in 12 cases was 0.52 ± 0.20 μg per ml of serum, showing no sexual difference.

Effects of Q metabolites and related compounds on mitochondrial succinate and NADH oxidase systems

The effects of Q metabolites (Q acid-I, Q acid-II) and related compounds (dihydro Q acid-I, dehydro Q acid-II, QS-n, and their esters) on mitochondrial succinate and NADH oxidase systems were investigated. The activity restoring succinate oxidation in acetone-treated beef heart mitochondria was found to decrease with descending order of carbon number (n) of the side chain of the Q metabolites; activity was restored with Q acid-I (n = 7) to one-third as much as that with Q-7 and Q-10, but Q acid-II (n = 5) did not restore any activity. Of the related compounds with a carboxyalkyl group (QS-n), QS-16-QS-18 (n = 16-18) were found to be most active, and their activities were also correlated with n. The relationship between the restoration of activity and the partition coefficient was considered. NADH oxidation in pentane-treated beef heart submitochondrial particles could be restored with esters of low molecular weight quinones to the same extent as with Q-10, but not with the metabolites.

Quinones of Brevibacterium.

Abstract Two unusual menaquinones have been revealed during examination of Brevibacterium thiogenitalis and Brevibacterium vitarumen. Both microorganisms were found to contain menaquinones-8 (II-H2) and -9 (II-H2). The major quinone of the former was menaquinone-9 (II-H2) while that of the latter was menaquinone-8 (II-H2). No ubiquinones were demonstrated in both microorganisms.

Ubiquinone and related compounds XX. Coenzymatic activity of ubiquinone and related compounds (II)

Abstract An enzyme preparation which requires the addition of Q alone for the restoration of the succinate oxidase system and is stable during a considerable period was obtained by the acetone-extraction procedure from rat-liver mitochondria. Structure-activity relationships of Q were investigated using this preparation and the trans-2′,3′-double bond in the isoprenoid side chain was found to be essential for maximum restoration of succinate oxidase activity.

[222] Gas chromatography of ubiquinone and related quinones

Publisher Summary This chapter discusses a gas chromatographic procedure for the extraction of ubiquinone (Q) and related quinines. The analysis of Q is usually carried out by the ultraviolet method on each homolog. When several homologs coexist, it is advantageous to apply a gas chromatographic procedure that does not comprise a separation for each homolog. For concentration, the lipid fraction is extracted and the Q fraction is separated from the other lipids. Methods that may possibly lead to some alterations in Q, such as alkaline hydrolysis, should not be used in the course of concentration, and it is preferable to obtain the Q fraction by simple solvent extraction and chromatography. For extraction of lipid from natural material without any loss of Q, the original material is treated with a hydrophilic organic solvent, such as a lower alcohol, with warming, and the extract is further treated with a lipophilic solvent, such as hexane. A lipid fraction is obtained by evaporation of the extract.