| 1. |
- Alpeeva, I, et al.
(författare)
-
Cyclometalated Ruthenium(II) Complexes As Efficient Redox Mediators in Peroxidase Catalysis
- 2003
-
Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 1432-1327 .- 0949-8257. ; 8:6, s. 683-688
-
Tidskriftsartikel (refereegranskat)abstract
- Cyclometalated ruthenium(II) complexes, [Ru II(C~N)(N~N) 2]PF 6 [HC~N=2-phenylpyridine (Hphpy) or 2-(4'-tolyl)pyridine; N~N=2,2'-bipyridine, 1,10-phenanthroline, or 4,4'-dimethyl-2,2'-bipyridine], are rapidly oxidized by H 2O 2 catalyzed by plant peroxidases to the corresponding Ru III species. The commercial isoenzyme C of horseradish peroxidase (HRP-C) and two recently purified peroxidases from sweet potato (SPP) and royal palm tree (RPTP) have been used. The most favorable conditions for the oxidation have been evaluated by varying the pH, buffer, and H 2O 2 concentrations and the apparent second-order rate constants ( k app) have been measured. All the complexes studied are oxidized by HRP-C at similar rates and the rate constants k app are identical to those known for the best substrates of HRP-C (10 6–10 7 M -1 s -1). Both cationic (HRP-C) and anionic (SPP and RPTP) peroxidases show similar catalytic efficiency in the oxidation of the Ru II complexes. The mediating capacity of the complexes has been evaluated using the SPP-catalyzed co-oxidation of [Ru II(phpy)(bpy) 2]PF 6 and catechol as a poor peroxidase substrate as an example. The rate of enzyme-catalyzed oxidation of catechol increases more than 10,000-fold in the presence of the ruthenium complex. A simple routine for calculating the rate constant k c for the oxidation of catechol by the Ru III complex generated enzymatically from [Ru II(phpy)(bpy) 2] + is proposed. It is based on the accepted mechanism of peroxidase catalysis and involves spectrophotometric measurements of the limiting Ru II concentration at different concentrations of catechol. The calculated k c value of 0.75 M -1 s -1 shows that the cyclometalated Ru II complexes are efficient mediators in peroxidase catalysis.
|
|
| 2. |
- Castillo Leon, Jaime, et al.
(författare)
-
Purification and substrate specificity of peroxidase from sweet potato tubers
- 2002
-
Ingår i: Plant Science. - 0168-9452. ; 163:5, s. 1011-1019
-
Tidskriftsartikel (refereegranskat)abstract
- Previously the screening of tropical plants demonstrated a high peroxidase activity in sweet potato (Ipomoea batatas) tubers. The major peroxidase pool is localized in peel. Using peel of sweet potato as a source, the sweet potato peroxidase (SPP) has been isolated and purified to homogeneity. The enzyme purification included homogenization, extraction of colored compounds and consecutive chromatographies on Phenyl-Sepharose and DEAE-Toyopearl. The purified SPP had specific activity of 4900 U mg(-1) protein, RZ (ratio of absorbances at 403 and 280 nm, respectively) 3.4, molecular mass of 37 kDa and isoelectric point of 3.5. The spectrum of peroxidase from sweet potato is typical for plant peroxidases with a Soret maximum at 401 nm and the maxima in the visible region at 497 and 638 nm, respectively. The substrate specificity of SPP is distinct from the specificity of other plant peroxidases, ferulic acid being the best substrate for SPP.
|
|
| 3. |
- Sparr, Emma, et al.
(författare)
-
Islet amyloid polypeptide-induced membrane leakage involves uptake of lipids by forming amyloid fibers
- 2004
-
Ingår i: FEBS Letters. - : Wiley. - 1873-3468 .- 0014-5793. ; 577:1-2, s. 117-120
-
Tidskriftsartikel (refereegranskat)abstract
- Fibril formation of islet amyloid polypeptide (IAPP) is associated with cell death of the insulin-producing pancreatic beta-cells in patients with Type 2 Diabetes Mellitus. A likely cause for the cytotoxicity of human TAPP is that it destroys the barrier properties of the cell membrane. Here, we show by fluorescence confocal microscopy on lipid vesicles that the process of hIAPP amyloid formation is accompanied by a loss of barrier function, whereby lipids are extracted from the membrane and taken up in the forming amyloid deposits. No membrane interaction was observed when preformed fibrils were used. It is proposed that lipid uptake from the cell membrane is responsible for amyloid-induced membrane damage and that this represents a general mechanism underlying the cytotoxicity of amyloid forming proteins. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
|
|
