Heme active-site structural characterization of chloroperoxidase by resonance raman spectroscopy
1993
Hu, S. | Kincaid, J.R.
Resonance Raman spectra are reported for the nitric oxide adducts of ferric and ferrous chloroperoxidase and carbon monoxide adducts of ferrous chloroperoxidase. The stretching, v(Fe-NO), and bending, delta(FeNO), modes are detected at 538 and 558 cm-1, respectively, for the ferric nitrosylchloroperoxidase. These two bands shift to 534 and 546 cm-1, respectively, upon substitution by (15)N(16)O. The v(Fe-NO) mode of the nitric oxide adduct of ferrous chloroperoxidase is located at 542 cm-1, which shifts to 528 ((15)n(16)O), 540 ((14)N(18)O), and 524 ((15)N(18)O) cm-1 as the mass of the bound nitric oxide increases by 1 atomic unit. Two distinct states of the carbon monoxide adduct of chloroperoxidase, the acidic and alkaline forms, are found to undergo a reversible pH-induced transition. The v(Fe-CO) mode shifts from 484 to 492 cm-1 and the delta(FeCO) mode at 562 cm-1 disappears as the pH is reduced from 6.0 to 3.3. In addition, two low frequency modes at 382 and 420 cm-1, assignable to the delta(C(b)C(1)C(2)) bending of propionate and vinyl groups, respectively, also show pH sensitivity. The results suggest a peroxidase-like heme active-site environment for chloroperoxidase and indicate a facile conformational change of heme groups accompanying the acid-base transition.
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