当前位置： SCI文献检索 > BIOCHEMISTRY期刊下所有文献 > Probing the heme iron coordination structure of alkaline chloroperoxidase.

Probing the heme iron coordination structure of alkaline chloroperoxidase.

Abstract：

:The mechanism by which the heme-containing peroxidase, chloroperoxidase, is able to chlorinate substrates is poorly understood. One approach to advance our understanding of the mechanism of the enzyme is to determine those factors which contribute to its stability. In particular, under alkaline conditions, chloroperoxidase undergoes a transition to a new, spectrally distinct form, with accompanying loss of enzymatic activity. In the present investigation, ferric and ferrous alkaline chloroperoxidase (C420) have been characterized by electronic absorption, magnetic circular dichroism, and electron paramagnetic resonance spectroscopy. The heme iron oxidation state influences the transition to C420; the pKa for the alkaline transition is 7.5 for the ferric protein and 9.5 for the ferrous protein. The five-coordinate, high-spin ferric native protein converts to a six-coordinate low-spin species (C420) as the pH is raised above 7.5. The inability of ferric C420 to bind exogenous ligands, as well as the dramatically increased reactivity of the proximal Cys29 heme ligand toward modification by the sulfhydryl reagent p-mercuribenzoate, suggests that a conformational change has occurred during conversion to C420 that restricts access to the peroxide binding site while increasing the accessibility of Cys29. However, it does appear that Cys29-derived ligation is at least partially retained by ferric C420, potentially in a thiolate/imidazole coordination sphere. Ferrous C420, on the other hand, appears not to possess a thiolate ligand but instead likely has a bis-imidazole (histidine) coordination structure. The axial ligand trans to carbon monoxide in ferrous-CO C420 may be a histidine imidazole. Since chloroperoxidase functions normally through the ferric and higher oxidation states, the fact that the proximal thiolate ligand is largely retained in ferric C420 clearly indicates that additional factors such as the absence of a vacant sixth coordination site sufficiently accessible for peroxide binding may be the cause of catalytic inactivity.

journal_name

Biochemistry

journal_title

Biochemistry

authors

Blanke SR,Martinis SA,Sligar SG,Hager LP,Rux JJ,Dawson JH

doi

10.1021/bi961512m

subject

Has Abstract

pub_date

1996-11-19 00:00:00

pages

14537-43

issue

eissn

0006-2960

issn

1520-4995

pii

bi961512m

journal_volume

pub_type

杂志文章

在线工具

Probing the heme iron coordination structure of alkaline chloroperoxidase.