Activation parameters for nitric oxide binding to Alcaligenes xylosoxidans cytochrome c′: Probing the putative dinitrosyl heme intermediate

CHED 769

Christine A. Petersen, petersc2@eou.edu1, David A. Pixton, pixtond@eou.edu1, Rudi van Eldik, vaneldik@chemie.uni-erlangen.de2, and Colin R. Andrew, candrew@eou.edu1. (1) Department of Chemistry & Biochemistry, Eastern Oregon University, 1, University Boulevard, La Grande, OR 97850, (2) Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstr. 1, Erlangen, 91058, Germany
Alcaligenes xylosoxidans cytochrome c′ (AXCP) is a heme protein with a pentacoordinate heme center. Interestingly, AXCP generates a five-coordinate heme-nitrosyl complex (5c-NO) in which nitric oxide (NO) binds to the proximal (rather than distal) heme face. A model has been proposed in which NO first binds to the distal heme face form a six-coordinate heme-nitrosyl (6c-NO) intermediate which then converts to the proximal 5c-NO complex via a putative dinitrosyl intermediate. Although the dinitrosyl species has not been observed, its existence is postulated from the proximal coordination of the 5c-NO end product, together with the NO-dependence of the 6c-NO→5c-NO conversion rate. In this study, activation parameters for NO binding to AXCP have been determined from the effect of temperature and hydrostatic pressure on rate constants. The results are discussed in terms of the mechanisms for distal and proximal NO binding, with particular emphasis on the formation of the dinitrosyl intermediate.
 

Undergraduate Research Poster Session: Biochemistry
2:00 PM-4:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Poster

Division of Chemical Education

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008