Binding of isotopically labeled substrates, inhibitors, and cyanide by protocatechuate 3,4-dioxygenase

A. M. Orville, J. D. Lipscomb

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

Binding of ligands to the active site Fe3+ of protocatechuate 3,4-dioxygenase is investigated using EPR-detected transferred hyperfine coupling from isotopically labeled substrates, inhibitors, and cyanide. Broadening is observed in EPR resonances from the anaerobic enzyme complex with homoprotocatechuate (3,4-dihydroxyphenylacetate), a slow substrate, enriched with 17O (I = 5/2) in either the 3-OH or the 4-OH group. This shows that this substrate binds directly to the Fe3+ and strongly suggests that an iron chelate can be formed. Cyanide is known to bind to the enzyme in at least two steps, forming first a high spin and then a low spin complex (Whittaker, J.W., and Lipscomb, J.D. (1984) J. Biol. Chem. 259, 4487-4495). Hyperfine broadening from [13C]cyanide (I = 1/2 ) is observed in the EPR spectra of both complexes, showing that cyanide is an Fe3+ ligand in each case. Cyanide binding is also at least biphasic in the presence of protocatechuate (PCA). The initial high spin enzyme-PCA-cyanide complex forms rapidly and exhibits a unique EPR spectrum. Broadening from PCA enriched with 17O in either the 3-OH or the 4-OH group is detected showing that PCA binds to the iron, probably as a chelate complex. In contrast, no broadening from [13C]cyanide is detected for this complex suggesting that cyanide binds at a site away from the Fe3+. Steady state kinetic measurements of cyanide inhibition of PCA turnover are consistent with two rapidly exchanging cyanide binding sites that inhibit PCA binding and which can be simultaneously occupied. Formation of the nearly irreversible, low spin enzyme-PCA-cyanide complex is competitively inhibited by PCA. Transient kinetics of the formation of this complex are second order in cyanide implying that two cyanides bind. Broadening in the EPR spectrum of this complex is detected from [13C]cyanide, but not from [17O]PCA, suggesting that PCA is displaced. This study provides the first direct evidence for chelation of the active site Fe3+ by substrates and for a small molecule binding site away from the iron in intradiol dioxygenases.

Original languageEnglish (US)
Pages (from-to)8791-8801
Number of pages11
JournalJournal of Biological Chemistry
Volume264
Issue number15
StatePublished - Jan 1 1989

Fingerprint

Protocatechuate-3,4-Dioxygenase
Cyanides
Substrates
Paramagnetic resonance
Enzymes
Catalytic Domain
Iron
Binding Sites
Iron Chelating Agents
Ligands
Dioxygenases

Cite this

Binding of isotopically labeled substrates, inhibitors, and cyanide by protocatechuate 3,4-dioxygenase. / Orville, A. M.; Lipscomb, J. D.

In: Journal of Biological Chemistry, Vol. 264, No. 15, 01.01.1989, p. 8791-8801.

Research output: Contribution to journalArticle

@article{d7849435ec704f75b93d54cfa8db33b6,
title = "Binding of isotopically labeled substrates, inhibitors, and cyanide by protocatechuate 3,4-dioxygenase",
abstract = "Binding of ligands to the active site Fe3+ of protocatechuate 3,4-dioxygenase is investigated using EPR-detected transferred hyperfine coupling from isotopically labeled substrates, inhibitors, and cyanide. Broadening is observed in EPR resonances from the anaerobic enzyme complex with homoprotocatechuate (3,4-dihydroxyphenylacetate), a slow substrate, enriched with 17O (I = 5/2) in either the 3-OH or the 4-OH group. This shows that this substrate binds directly to the Fe3+ and strongly suggests that an iron chelate can be formed. Cyanide is known to bind to the enzyme in at least two steps, forming first a high spin and then a low spin complex (Whittaker, J.W., and Lipscomb, J.D. (1984) J. Biol. Chem. 259, 4487-4495). Hyperfine broadening from [13C]cyanide (I = 1/2 ) is observed in the EPR spectra of both complexes, showing that cyanide is an Fe3+ ligand in each case. Cyanide binding is also at least biphasic in the presence of protocatechuate (PCA). The initial high spin enzyme-PCA-cyanide complex forms rapidly and exhibits a unique EPR spectrum. Broadening from PCA enriched with 17O in either the 3-OH or the 4-OH group is detected showing that PCA binds to the iron, probably as a chelate complex. In contrast, no broadening from [13C]cyanide is detected for this complex suggesting that cyanide binds at a site away from the Fe3+. Steady state kinetic measurements of cyanide inhibition of PCA turnover are consistent with two rapidly exchanging cyanide binding sites that inhibit PCA binding and which can be simultaneously occupied. Formation of the nearly irreversible, low spin enzyme-PCA-cyanide complex is competitively inhibited by PCA. Transient kinetics of the formation of this complex are second order in cyanide implying that two cyanides bind. Broadening in the EPR spectrum of this complex is detected from [13C]cyanide, but not from [17O]PCA, suggesting that PCA is displaced. This study provides the first direct evidence for chelation of the active site Fe3+ by substrates and for a small molecule binding site away from the iron in intradiol dioxygenases.",
author = "Orville, {A. M.} and Lipscomb, {J. D.}",
year = "1989",
month = "1",
day = "1",
language = "English (US)",
volume = "264",
pages = "8791--8801",
journal = "Journal of Biological Chemistry",
issn = "0021-9258",
publisher = "American Society for Biochemistry and Molecular Biology Inc.",
number = "15",

}

TY - JOUR

T1 - Binding of isotopically labeled substrates, inhibitors, and cyanide by protocatechuate 3,4-dioxygenase

AU - Orville, A. M.

AU - Lipscomb, J. D.

PY - 1989/1/1

Y1 - 1989/1/1

N2 - Binding of ligands to the active site Fe3+ of protocatechuate 3,4-dioxygenase is investigated using EPR-detected transferred hyperfine coupling from isotopically labeled substrates, inhibitors, and cyanide. Broadening is observed in EPR resonances from the anaerobic enzyme complex with homoprotocatechuate (3,4-dihydroxyphenylacetate), a slow substrate, enriched with 17O (I = 5/2) in either the 3-OH or the 4-OH group. This shows that this substrate binds directly to the Fe3+ and strongly suggests that an iron chelate can be formed. Cyanide is known to bind to the enzyme in at least two steps, forming first a high spin and then a low spin complex (Whittaker, J.W., and Lipscomb, J.D. (1984) J. Biol. Chem. 259, 4487-4495). Hyperfine broadening from [13C]cyanide (I = 1/2 ) is observed in the EPR spectra of both complexes, showing that cyanide is an Fe3+ ligand in each case. Cyanide binding is also at least biphasic in the presence of protocatechuate (PCA). The initial high spin enzyme-PCA-cyanide complex forms rapidly and exhibits a unique EPR spectrum. Broadening from PCA enriched with 17O in either the 3-OH or the 4-OH group is detected showing that PCA binds to the iron, probably as a chelate complex. In contrast, no broadening from [13C]cyanide is detected for this complex suggesting that cyanide binds at a site away from the Fe3+. Steady state kinetic measurements of cyanide inhibition of PCA turnover are consistent with two rapidly exchanging cyanide binding sites that inhibit PCA binding and which can be simultaneously occupied. Formation of the nearly irreversible, low spin enzyme-PCA-cyanide complex is competitively inhibited by PCA. Transient kinetics of the formation of this complex are second order in cyanide implying that two cyanides bind. Broadening in the EPR spectrum of this complex is detected from [13C]cyanide, but not from [17O]PCA, suggesting that PCA is displaced. This study provides the first direct evidence for chelation of the active site Fe3+ by substrates and for a small molecule binding site away from the iron in intradiol dioxygenases.

AB - Binding of ligands to the active site Fe3+ of protocatechuate 3,4-dioxygenase is investigated using EPR-detected transferred hyperfine coupling from isotopically labeled substrates, inhibitors, and cyanide. Broadening is observed in EPR resonances from the anaerobic enzyme complex with homoprotocatechuate (3,4-dihydroxyphenylacetate), a slow substrate, enriched with 17O (I = 5/2) in either the 3-OH or the 4-OH group. This shows that this substrate binds directly to the Fe3+ and strongly suggests that an iron chelate can be formed. Cyanide is known to bind to the enzyme in at least two steps, forming first a high spin and then a low spin complex (Whittaker, J.W., and Lipscomb, J.D. (1984) J. Biol. Chem. 259, 4487-4495). Hyperfine broadening from [13C]cyanide (I = 1/2 ) is observed in the EPR spectra of both complexes, showing that cyanide is an Fe3+ ligand in each case. Cyanide binding is also at least biphasic in the presence of protocatechuate (PCA). The initial high spin enzyme-PCA-cyanide complex forms rapidly and exhibits a unique EPR spectrum. Broadening from PCA enriched with 17O in either the 3-OH or the 4-OH group is detected showing that PCA binds to the iron, probably as a chelate complex. In contrast, no broadening from [13C]cyanide is detected for this complex suggesting that cyanide binds at a site away from the Fe3+. Steady state kinetic measurements of cyanide inhibition of PCA turnover are consistent with two rapidly exchanging cyanide binding sites that inhibit PCA binding and which can be simultaneously occupied. Formation of the nearly irreversible, low spin enzyme-PCA-cyanide complex is competitively inhibited by PCA. Transient kinetics of the formation of this complex are second order in cyanide implying that two cyanides bind. Broadening in the EPR spectrum of this complex is detected from [13C]cyanide, but not from [17O]PCA, suggesting that PCA is displaced. This study provides the first direct evidence for chelation of the active site Fe3+ by substrates and for a small molecule binding site away from the iron in intradiol dioxygenases.

UR - http://www.scopus.com/inward/record.url?scp=0024328715&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0024328715&partnerID=8YFLogxK

M3 - Article

C2 - 2542290

AN - SCOPUS:0024328715

VL - 264

SP - 8791

EP - 8801

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

SN - 0021-9258

IS - 15

ER -