Formation and decay of cytochrome c peroxidase compound ES during aerobic redution with dithionite

AbstractStopped-flow and rapid scanning studies have clearly demonstrated that mixing of an oxygen-saturated solution of yeast cytochrome c peroxidase with sodium dithionite yields compound ES, indicating generation of H2O2. The formation of compound ES was most pronounced when [Na2S2O4/[O2] ≈ 1, and it reverted to the ferric form while standing. Even in the presence of an excess of dithionite ([Na2S2O4]/[O2] = 3.4) compound ES was formed immediately, but was soon replaced by the ferric form, followed by its final reduction to the ferrous state. The apparent first order rate constant for the decay of compound ES to the ferric form increased linearly with the square root of the dithionite concentration, thus involvement of SO−2 in that process being suggested

Role of a bound ubiquinone on reactions of the Escherichia coli cytochrome bo with ubiquinol and dioxygen11This work was supported in part by Grants-in-Aid for Scientific Research on Priority Areas (08249106) and for Scientific Research (B) (08458202) from the Ministry of Education, Science, Sports and Culture, Japan. This is paper XXXIII in the series ‘Structure-function studies on the Escherichia coli cytochrome bo’.

AbstractTo probe the functional role of a bound ubiquinone-8 in cytochrome bo-type ubiquinol oxidase from Escherichia coli, we examined reactions with ubiquinol-1 and dioxygen. Stopped-flow studies showed that anaerobic reduction of the wild-type and the bound ubiquinone-free (ΔUbiA) enzymes with ubiquinol-1 immediately takes place with four kinetic phases. Replacement of the bound ubiquinone with 2,6-dibromo-4-cyanophenol (PC32) suppressed the anaerobic reduction of the hemes with ubiquinol-1 by eliminating the fast phase. Flow-flash studies in the reaction of the fully reduced enzyme with dioxygen showed that the heme b to heme o electron transfer occurs with a rate constant of ∼104 s−1 in all three preparations. These results support our previous proposal that the bound ubiquinone is involved in facile oxidation of substrates in subunit II and subsequent intramolecular electron transfer to low-spin heme b in subunit I

Comparison of the intraocular pressure following an intravitreal triamcinolone acetonide injection for diabetic macula oedema in vitrectomised and non-vitrectomised eyes

Purpose To compare the intraocular pressure (IOP) after an intravitreal triamcinolone acetonide (IVTA) between vitrectomised and non-vitrectomised eyes in patients with diabetes and diabetic macular oedema (DME).Design Retrospective comparative studyMethods Medical records of 157 patients (157 eyes) with type 2 diabetes who received IVTA for DME were reviewed, and the best-corrected visual acuity, IOP and optical central retinal thickness (CRT) were compared preoperatively, at 1, 4, 12 and 24 weeks after IVTA between the vitrectomised and non-vitrectomised groups.Results IOP significantly increased at 1 (p<0.0001), 4 (p<0.0001), 8 (p<0.0001), 12 (p=0.0019), 16 (p=0.0006) and 20 weeks (p=0.0191) in the non-vitrectomised group, whereas a significant increase was only observed at 1 (p=0.0003) and 4 weeks (p=0.0006) in the vitrectomised group. ΔIOP, IOP changes from baseline, in the non-vitrectomised group was significantly higher than that in the vitrectomised group at 4 (p=0.0014), 8 (p=0.0081), 12 (p=0.0032) and 16 weeks (p=0.0038). No significant difference was observed in logMAR and CRT at any time point after IVTA between the two groups.Conclusions After an initial IVTA, increased IOP and ΔIOP from the baseline IOP were significantly more frequently observed in the non-vitrectomised than that in the vitrectomised group. IVTA is a safer and more effective treatment option for DME in vitrectomised than that in non-vitrectomised eyes