BINDING OF IODIDE TO ARTHROMYCES-RAMOSUS PEROXIDASE INVESTIGATED WITHX-RAY CRYSTALLOGRAPHIC ANALYSIS, H-1 AND I-127 NMR-SPECTROSCOPY, AND STEADY-STATE KINETICS

Citation
K. Fukuyama et al., BINDING OF IODIDE TO ARTHROMYCES-RAMOSUS PEROXIDASE INVESTIGATED WITHX-RAY CRYSTALLOGRAPHIC ANALYSIS, H-1 AND I-127 NMR-SPECTROSCOPY, AND STEADY-STATE KINETICS, The Journal of biological chemistry, 272(9), 1997, pp. 5752-5756
Citations number
55
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
272
Issue
9
Year of publication
1997
Pages
5752 - 5756
Database
ISI
SICI code
0021-9258(1997)272:9<5752:BOITAP>2.0.ZU;2-W
Abstract
The site and characteristics of iodide binding to Arthromyces ramosus peroxidase were examined by x-ray crystallographic analysis, H-1 and I -127 NMR and kinetic studies. X-ray analysis of an A. ramosus peroxida se crystal soaked in a KI solution at pH 5.5 showed that a single iodi de ion is located at the entrance of the access channel to the distal side of the heme and Lies between the two peptide segments, Phe(90)-Pr o(91)-Ala(92) and Ser(151)-Leu(152)-Ile(153), 12.8 Angstrom from the h eme iron, The distances between the iodide ion and heme peripheral met hyl groups were all more than 10 Angstrom. The findings agree with the results obtained with H-1 NMR in which the chemical shift and intensi ty of the methyl groups in the hyperfine shift region of A. ramosus pe roxidase were hardly affected by the addition of iodide, unlike the ca se of horseradish peroxidase. Moreover, I-127 NMR and steady-state kin etics showed that the binding of iodide depends on protonation of an a mino acid residue with a pK(a) of about 5.3, which presumably is the d istal histidine (His(56)), 7.8 Angstrom away from the iodide ion. The mechanism of electron transfer from the iodide ion to the heme iron is discussed on the basis of these findings.