Disease relevance of Qi

• Pulsed EPR spectroscopy was used to explore the structural neighborhood of the semiquinone (SQ) stabilized at the Qi site of the bc1 complex of Rhodobacter sphaeroides (EC 1.10.2.2) and to demonstrate that the nitrogen atom of a histidine imidazole group donates an H-bond to the SQ [1].
• This installment includes basic instruction in the technique, and a discussion of the dyskinesia which occurs during restoration of Qi to the Large Intestine and Stomach channels during treatment [2].
• We have demonstrated previously that human breast cancer cells regain the ability to express OCT3 mRNA [Jin, Branch, Zhang, Qi, Youngson and Goss (1999) Int. J. Cancer 81, 104-112] [3].

High impact information on Qi

• Here we report that in mature striatal neurons in primary cultures, quisqualate can release arachidonic acid by associatively activating both quisqualate metabotropic receptors coupled to phospholipase C (Qp) and Qi receptors [4].
• Associative stimulation of N-methyl-D-aspartate (NMDA) receptors and quisqualate ionotropic receptors (Qi) induces long-term potentiation at particular glutamatergic synapses [4].
• Interestingly, the occupancy of quinone in the Qi site is higher in the monomer with bound cytochrome c, suggesting a coordinated binding and reduction of both electron-accepting substrates [5].
• The presence or absence of the Qi inhibitor antimycin A did not affect the binding of the Qo inhibitors [6].
• We have analyzed crystal structures of cytochrome bc1 complexes with electron transfer inhibitors bound to the ubiquinone binding pockets Qi and/or Qo in the cytochrome b subunit [6].

Biological context of Qi

• The protonmotive cytochrome b protein of the mitochondrial bc1 respiratory chain complex contains two reactions centers, designated Qo and Qi, which can be distinguished by the effects of different inhibitors [7].
• External Qi of YXLST also upregulated IGF-I gene expression and increased PI3K activity [8].
• Previous work (Qi, W., Fong, C., Lamport, D.T.A., 1991. Plant Physiology 96, 848), suggested small (approximately 11 residue) repetitive peptide motifs each with three Hyp-arabinoside attachment sites and a single Hyp-arabinogalactan polysaccharide attachment site [9].
• Acupuncture until De Qi is effectively equivalent to charging the capacitor Ceq of the RLC resonator in the transmission line [10].

Associations of Qi with chemical compounds

• In an alternative model, the semiquinone cycle [Wikström, M. & Krab, K. (1986) J. Bioenerg. Biomembr. 18, 181-193], a charged semiquinone formed at site Qo is transferred to site Qi where it is reduced into quinol [11].
• Crystallographic structures show two different configurations for the binding of ubiquinone at the Qi site of mitochondrial bc1 complexes in which histidine (His-201 in bovine sequence) is either a direct H-bond donor or separated by a bridging water [1].
• Kinetic effects of the electrochemical proton gradient on plastoquinone reduction at the Qi site of the cytochrome b6f complex [12].
• The antimycin-sensitive SQ formed at the Qi site by either equilibrium redox titration, reduction of the oxidized complex by ascorbate, or addition of decylubihydroquinone to the oxidized complex in the presence of myxothiazol all showed similar properties [1].
• We previously demonstrated that secretion of dense granule proteins in permeabilized parasites was augmented by the non-hydrolyzable GTP analogue guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) (Chaturvedi, S., Qi, H., Coleman, D. L., Hanson, P., Rodriguez, A., and Joiner, K. A. (1998) J. Biol. Chem. 274, 2424-2431) [13].

Gene context of Qi

• We have recently isolated FYVE-DSP1, a FYVE domain-containing dual specificity protein phosphatase (R. Zhao, Y. Qi, and Z. J. Zhao, Biochem. Biophys. Res. Commun. 270, 222--229 (2000)) [14].
• The Q0 center is formed by the b-566 domain of cytochrome b, the FeS protein, and maybe an additional small subunit, whereas the Qi center is formed by the b-562 domain of cytochrome b and presumably the 13.4 kDa protein ("QP-C") [15].
• Antimycin and diuron appear to block cytochrome b oxidation-reduction at one ubiquinone site, presumably Qi [16].
• Neuronal Cdc2-like kinase is a heterodimer of Cdk5 and a 25-kDa subunit which is derived from a brain-specific 35-kDa novel protein, p35 (Lew, J., Huang, Q.-Q., Qi, Z., Winkfein, R. J., Aebersold, R., Hunt, T., and Wang, J. H. (1994) Nature 371, 423-426) [17].
• The cytochrome b subunit of the bc1 complexes contains two cytochrome components (bL and bH) and is the locus of both a quinol-oxidizing site (Qo or Qz) and a quinone-reducing site (Qi or Qc) [18].

Analytical, diagnostic and therapeutic context of Qi

• For this purpose, we measured: (1) the washouts of perfused 133 Xenon (Xe) in the whole lung and in 6 horizontal slices of the right lung, and (2) the topographical distribution of perfusion (Qi) in 27 healthy, non-smoking seated men, between 18 and 65 years [19].

References