| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 1999: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1998: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
Horse heart metmyoglobin (metMb), whose lysine residues were modified with diethylenetriaminepentaacetic acid (DTPA), was characterized by a MALDI-TOF mass spectroscopy, an amino-acid sequence analysis, and UV-Vis and CD spectroscopies. Kinetics of the oxidation of the reduced cytochrome c (cyt c(II)) wit hydrogen peroxide catalyzed by metMb(DTPA)ィイD2nィエD2(n = 1, 2, 4, and 5) was investigated spectrophotometrically compared with native metMb. The modified metMb(DTPA)ィイD2nィエD2 showed the cytochrome c peroxidase-like activity more efficiently than the native metMb (metMb(DTPA)ィイD25ィエD2 > metMb(DTPA)ィイD24ィエD2 > metMb(DTPA)ィイD22ィエD2 > metMbDTPA 【greater than or equal】 native metMb). The native metMb does not bind cyt c(II), but metMb(DTPA)ィイD2nィエD2 can bind cyt c(II) with an anionic patch where DTPA anions are liked to the Lys residue(s) on the surface of metMb. The formation of the diprotein complex of metMb(DTPA)ィイD2nィエD2 with cyt c(II) accelerates the electron-transfer (ET) reaction fro
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m cyt c(II) to ferrylMb. An intermediate ferrylMb-protein radical was also detected by an ESR measurement ; it might be a Tyr146 radical. The photoinduced ET reaction between cyt c(III) and zinc-substituted myoglobin modified with DTPA ions, was reexamined. The first-order rate constant for the concentrations of cyt c(III), suggesting ZnMb(DTPA)ィイD2nィエD2(n = 2, 4, and 5) was saturated with increasing the concentrations of cyt c(III), suggesting that the ET quenching occurs within a diprotein complex. The formation constant for the diprotein complex increased with increasing the number of DTPA ions on the lysine residues of myoglobin and decreased with increasing ionic strength, indicating that cyt c(III) interacts with the DTPA anionic patch. The intermolecular ET rate constants in the diprotein complex increased with increasing the number of DTPA ions and decreased with increasing ionic strength. It is suggested that a gating occurs by fluctuation in the configuration of a diprotein complex. Less
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