Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.9.3.1 (cytochrome oxidase)
 8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Isolated mammalian cytochrome oxidase gave an Arrhenius plot with a break (Tb) at about 20 degrees C when assayed in a medium containing Emasol. The activation energies above and below 20 degrees C were 9.3 (EH) and 18.9 kcal/mol (EL), respectively. Isolated cytochrome oxidase was also incorporated into vesicles of dipalmitoyl phosphatidylcholine (DPPC, phase transition temperature Tt = 40 degrees C), dimyristoyl phosphatidylcholine (DMPC, Tt = 23 degrees C) and dioleoyl phosphatidylcholine (DOPC, Tt = -22 degrees C). The DPPC system showed a nearly linear Arrhenius plot between 9 and 36 degrees C with E = 22.8 kcal/mol. When cytochrome oxidase was resolubilized from the DPPC vesicles and assayed in solution a biphasic plot was obtained again. Cytochrome oxidase-DOPC was more active than the solubilized enzyme and exhibited a biphasic Arrhenius plot with Tb = 23 degrees C. EH and EL were 6.6 and 15.8 kcal/mol, respectively. The plot for the oxidase-DMPC also showed a break (Tb = 26 degrees C) with EH = 6.6 and EL = 26.6 kcal/mol. These results indicate that the break in the Arrhenius plot reflects primarily a structural transition in the cytochrome oxidase molecule between the "hot" and "cold" conformations, as proposed previously. This transition, as well as the molecular state of cytochrome oxidase, is affected by the physical state of the membrane lipids as reflected by changes in the kinetic properties.
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PMID:Effects of temperature on cytochrome oxidase activity in solubilized form and in lipid vesicle systems. 23 Jan 86

The reactivation of delipidated cytochrome oxidase depends on the reformation of "annular lipids", which is tightly bounded to the enzyme molecule. In the restoration of oxidase activity, the efficiencies of phospholipids with different polar head groups decrease in this order: PS greater than DPG greater than PI greater than PA greater than PG greater than PC, PE and in the case of phosphatidylcholines with different acyl chain the order is DOPC greater than LPC greater than PC greater than DPPC, DSPC. Therefore both the polar head group and the acyl chain of phospholipids must be considered in the reactivation process. The existence and the specificity of "annular lipids" obviously influence the incorporation of cytochrome oxidase into liposomes. When acidic phospholipids are used as "annular lipids", the effectiveness of reconstitution decreases in this order: PI greater than PS greater than DPG greater than PA, PG. Divalent metallic cations would facilitate the cytochrome oxidase reconstitution, but their effects depend on the composition of "annular lipids". Using dialysis method Ca2+ and Mg2+ could facilitate the incorporation into liposomes of the enzymes having PS or DOPC as their "boundary lipids". A comparison between the effects of different metallic cations on incorporation of cytochrome oxidase also shows that, with PI as "annular lipids", the effectiveness of different cations on incorporation by incubation method decreases in this order: Ca2+ greater than Mg2+ greater than Mn2+, Sr2+ greater than La3+. Apparently, the effect of metallic cations on incorporation cannot be interpreted by considering only the neutralization of the negative charged groups on membrane protein and lipids.
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PMID:Studies on the incorporation of membrane proteins into liposomes: --effect of "boundary lipids" on reconstitution of pig heart mitochondrial cytochrome oxidase into liposomes. 628 66