Spectroscopic investigation of reduced protocatechuate 3,4-dioxygenase: Charge-induced alterations in the active site iron coordination environment

Mindy I. Davis, Erik C. Wasinger, Tami E. Westre, Jeffrey M. Zaleski, Allen M. Orville, John D. Lipscomb, Britt Hedman, Keith O. Hodgson, Edward I. Solomon

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

Chemical reduction of the mononuclear ferric active site in the bacterial intradiol cleaving catecholic dioxygenase protocatechuate 3,4-dioxygenase (3,4-PCD, Brevibacterium fuscum) produces a high-spin ferrous center. We have applied circular dichroism (CD), magnetic circular dichroism (MCD), variable-temperature-variable-field (VTVH) MCD, X-ray absorption (XAS) pre-edge, and extended X-ray absorption fine structure (EXAFS) spectroscopies to investigate the geometric and electronic structure of the reduced iron center. Excited-state ligand field CD and MCD data indicate that the site is six-coordinate where the 5Eg excited-state splitting is 2033 cm-1. VTVH MCD analysis of the ground state indicates that the site has negative zero-field splitting with a small rhombic splitting of the lowest doublet (δ = 1.6 ± 0.3 cm-1). XAS pre-edge analysis also indicates a six-coordinate site while EXAFS analysis provides accurate bond lengths. Since previous spectroscopic analysis and the crystal structure of oxidized 3,4-PCD indicate a five-coordinate ferric active site, the results presented here show that the coordination number increases upon reduction. This is attributed to the coordination of a second solvent ligand. The coordination number increase relative to the oxidized site also appears to be associated with a large decrease in the ligand donor strength in the reduced enzyme due to protonation of the original hydroxide ligand.

Original languageEnglish (US)
Pages (from-to)3676-3683
Number of pages8
JournalInorganic Chemistry
Volume38
Issue number16
StatePublished - Dec 1 1999

Fingerprint Dive into the research topics of 'Spectroscopic investigation of reduced protocatechuate 3,4-dioxygenase: Charge-induced alterations in the active site iron coordination environment'. Together they form a unique fingerprint.

  • Cite this

    Davis, M. I., Wasinger, E. C., Westre, T. E., Zaleski, J. M., Orville, A. M., Lipscomb, J. D., Hedman, B., Hodgson, K. O., & Solomon, E. I. (1999). Spectroscopic investigation of reduced protocatechuate 3,4-dioxygenase: Charge-induced alterations in the active site iron coordination environment. Inorganic Chemistry, 38(16), 3676-3683.