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