title: Dynamic function of the alkyl spacer of acetogenins in their inhibitory action with mitochondrial complex I (NADH-ubiquinone oxidoreductase).
abstract: Studies on the inhibitory mechanism of acetogenins, the most potent inhibitors of mitochondrial complex I (NADH-ubiquinone oxidoreductase), are useful for elucidating the structural and functional features of the terminal electron transfer step of this enzyme. Previous studies of the structure-activity relationship revealed that except for the alkyl spacer linking the two toxophores (i.e., the hydroxylated THF and the gamma-lactone rings), none of the multiple functional groups of these inhibitors is essential for potent inhibition. To elucidate the function of the alkyl spacer, two sets of systematically selected analogues were synthesized. First, the length of the spacer was varied widely. Second, the local flexibility of the spacer was specifically reduced by introducing multiple bond(s) into different regions of the spacer. The optimal length of the spacer for inhibition was approximately 13 carbon atoms. The decrease in the strength of the inhibitory effect caused by elongating the spacer from 13 carbons was much more drastic than that caused by shortening. Local flexibility in a specific region of the spacer was not important for the inhibition. These observations indicate that the active conformation of the spacer is not an extended form, and is not necessarily restricted to a certain rigid shape. Moreover, an analogue in which a spacer covering 10 carbon atoms was hardened into a rodlike shape still maintained a potent inhibitory effect. Our results strongly suggest that the spacer portion is free from steric congestion arising from the putative binding site probably because there is no cavity-like binding site for the spacer portion. The manner of acetogenin binding to the enzyme may not be explained by a simple "key and keyhole" analogy.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Abe
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Murai
authors.forename: Naoya
authors.initials: N
authors.lastname: Ichimaru
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kenmochi
authors.forename: Takehiko
authors.initials: T
authors.lastname: Yoshida
authors.forename: Akina
authors.initials: A
authors.lastname: Kubo
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kimura
authors.forename: Aki
authors.initials: A
authors.lastname: Moroda
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Makabe
authors.forename: Takaaki
authors.initials: T
authors.lastname: Nishioka
authors.forename: Hideto
authors.initials: H
authors.lastname: Miyoshi
mesh_terms: D054378:Acetogenins; D001665:Binding Sites; D042967:Electron Transport Complex I / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D005233:Fatty Alcohols / Q000737:chemistry* / Q000494:pharmacology; D007783:Lactones / Q000737:chemistry* / Q000494:pharmacology; D008928:Mitochondria / Q000201:enzymology*; D008956:Models, Chemical; D013481:Superoxides / Q000378:metabolism
chemical_list: D054378:Acetogenins; D004791:Enzyme Inhibitors; D005233:Fatty Alcohols; D007783:Lactones; D013481:Superoxides; D042967:Electron Transport Complex I