5677-55-4Relevant academic research and scientific papers
A tightly bound quinone functions in the ubiquinone reaction sites of quinoprotein alcohol dehydrogenase of an acetic acid bacterium, Gluconobacter suboxydans
Matsushita, Kazunobu,Kobayashi, Yoshiki,Mizuguchi, Mitsuhiro,Toyama, Hirohide,Adachi, Osao,Sakamoto, Kimitoshi,Miyoshi, Hideto
, p. 2723 - 2731 (2008)
Quinoprotein alcohol dehydrogenase (ADH) of acetic acid bacteria is a membrane-bound enzyme that functions as the primary dehydrogenase in the ethanol oxidase respiratory chain. It consists of three subunits and has a pyrroloquinoline quinone (PQQ) in the active site and four heme c moieties as electron transfer mediators. Of these, three heme c sites and a further site have been found to be involved in ubiquinone (Q) reduction and ubiquinol (QH2) oxidation respectively (Matsushita et al., Biochim. Biophys. Acta, 1409, 154-164 (1999)). In this study, it was found that ADH solubilized and purified with dodecyl maltoside, but not with Triton X-100, had a tightly bound Q, and thus two different ADHs, one having the tightly bound Q (Q-bound ADH) and Q-free ADH, could be obtained. The Q-binding sites of both the ADHs were characterized using specific inhibitors, a substituted phenol PC16 (a Q analog inhibitor) and antimycin A. Based on the inhibition kinetics of Q2 reductase and ubiquinol-2 (Q2H2) oxidase activities, it was suggested that there are one and two PC16-binding sites in Q-bound ADH and Q-free ADH respectively. On the other hand, with antimycin A, only one binding site was found for Q2 reductase and Q2H2 oxidase activities, irrespective of the presence of bound Q. These results suggest that ADH has a high-affinity Q binding site (QH) besides low-affinity Q reduction and QH2 oxidation sites, and that the bound Q in the QH site is involved in the electron transfer between heme c moieties and bulk Q or QH2 in the low-affinity sites.
Design, synthesis, and photochemical properties of a photoreleasable ubiquinol-2: A novel compound for studying rapid electron-transfer kinetics in ubiquinol-oxidizing enzymes
Wang, Guangyang
, p. 1657 - 1664 (2007/10/03)
The design and multistep convergent synthesis of the novel photoactive ubiquinol-benzoin adduct 1a,b has been accomplished. Optical spectra of the steady-state photolysis reactions showed a smooth conversion from 1a,b to 5,7-dimethoxy-2-phenylbenzofuran (13) and ubiquinol-2 with an isobestic point at 258 nm. HPLC analysis of the photoproducts was also consistent with the clean formation of the desired ubiquinol-2 (3) and the expected 5,7-dimethoxy-2-phenylbenzofuran (2). Transient photolysis at 355 nm was consistent with a rapid photolysis rate that exceeded the instrument response time (> 106 s-1). Accordingly, the study of rapid electron-transfer events in ubiquinol oxidizing enzymes is now feasible. Furthermore, the synthetic methods developed herein will be of general application for the facile synthesis of a variety of photoreleasable substrates for studying rapid kinetic events in enzymatic reactions.
The surprisingly high reactivity of phenoxyl radicals
Foti,Ingold,Lusztyk
, p. 9440 - 9447 (2007/10/02)
Rate constants have been measured in nonaqueous media for hydrogen atom abstraction by the phenoxyl radical from some biologically important phenols and related compounds. Although the thermochemistry for these reactions must be very similar to the thermochemistry for H atom abstraction from the same substrate by a peroxyl radical, the phenoxyl rate constants, k5, are ca. 100-300 times greater than the (already well-known) peroxyl rate constants, k1. For example, with α-tocopherol in benzene/di-tert-butyl peroxide (1:3, v/v) k5293K = 1.1 × 109 M-1 s-1 vs k1303K = 3.2 × 106 M-1 s-1 in a similar nonpolar medium, and with ubiquinol-10 in the same solvent mixture k5293k = 8.4 × 107 M-1 s-1, while the corresponding value for k1 is 3.5 × 105 M-1 s-1. The greater reactivity of the phenoxyl radical has been traced to the fact that the Arrhenius preexponential factors are much larger than for the corresponding peroxyl radical reactions, i.e., A5 ～ 102A1. For example, with α-naphthol log(A5/M-1 s-1) = 8.9 and E5 = 2.2 kcal/mol vs log(A1/M-1 s-1) = 6.4 and E1 = 1.7 kcal/mol. The preexponential factors for H-atom donors more reactive than α-naphthol are even greater; for example, with α-tocopherol in CH3CN/di-tert-butyl peroxide (1:2, v/v) log(A5/M-1 s-1) = 10.0 and E5 = 2.0 kcal/mol, and with ubiquinol-0 in benzene/di-tert-butyl peroxide (1:3, v/v) log(A5/M-1 s-1) = 10.5 and E5 = 3.5 kcal/mol. The role that intermediate hydrogen-bonded complexes between the reacting radical and the phenolic hydrogen donor may play in these reactions is discussed, and it is pointed out that our results are likely to be relevant to in vivo radical chemistry.
REGIOSELECTIVE POLYPRENYL REARRANGEMENT OF POLYPRENYL 2,3,4,5-TETRASUBSTITUTED PHENYL ETHERS PROMOTED BY BORON TRIFLUORIDE
Yoshizawa, Toyokichi,Toyofuku, Hatsunori,Tachibana, Koichi,Kuroda, Toshio
, p. 1131 - 1134 (2007/10/02)
4-Acetoxy-6-polyprenyl-2,3,5-trimethylphenols or 2,3-dimethoxy-5-methyl-6-polyprenylhydroquinones were obtained selectively by the BF3*OEt2 catalyzed polyprenyl rearrangement of polyprenyl 4-acetoxy-2,3,5-trimethylphenyl ethers or polyprenyl 2,3-dimethoxy-4-hydroxy-5-methylphenyl ethers.
Quinones. Part 2. General Synthetic Routes to Quinone Derivatives with Modified Polyprenyl Side Chains and the Inhibitory Effects of these Quinones on the Generation of the Slow Reacting Substance of Anaphylaxis (SRS-A)
Terao, Shinji,Shiraishi, Mitsuru,Kato, Kaneyoshi,Ohkawa, Shigenori,Ashida, Yasuko,Maki, Yoshitaka
, p. 2909 - 2920 (2007/10/02)
General synthetic routes to quinone acids (8), quinone amides (9), quinone alcohols (10), and quinone methylketones (11) with polyprenyl side chains, in which allylic alcohols (3) are employed as the key intermediates, are described.The Claisen rearrangements and the Carrol reactions of the allylic alcohols (3) with ethyl orthoacetate and diketen produced the ethyl esters (4) and the methylketones (5), respectively.Quinone products (8), (10), and (11) were recovered by oxidative demethylation of hydroquinone dimethyl ethers (4), (5), and (7) or by acid hydrolysis of hydroquinone bis(methoxymethyl) ethers (4) and (5) followed by ferric chloride oxidation.Amidation of quinone acids (8) led to the formation of quinone amides (9).Inhibitory effects of these quinone derivatives on the generation of the slow reacting substance of anaphylaxis (SRS-A) in the lungs of sensitised guinea pigs are evaluated.
