Chicken liver sulfite oxidase. Kinetics of reduction by laser-photoreduced flavins and intramolecular electron transfer

Laser flash photolysis was used to study the reaction of photoproduced 5-deazariboflavin (dRFH.), lumiflavin (LFH.), and riboflavin (RFH.) semiquinone radicals with the redox centers of purified chicken liver sulfite oxidase. Kinetic studies of the native enzyme with dRFH. yielded a second-order rat...

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Bibliographic Details
Published in:Biochemistry (Easton) 1988-04, Vol.27 (8), p.2918-2926
Main Authors: Kipke, Cary A, Cusanovich, Michael A, Tollin, Gordon, Sunde, Roger A, Enemark, John H
Format: Article
Language:English
Subjects:
ACTIVIDAD ENZIMATICA
ACTIVITE ENZYMATIQUE
Animals
Biological and medical sciences
CHICKENS
Electrochemistry
electron transfer
Electron Transport
ENZYMIC ACTIVITY
Flavins - pharmacology
FOIE
Fundamental and applied biological sciences. Psychology
HIGADO
Kinetics
LASER RADIATION
Lasers
LIVER
Liver - enzymology
Molecular biophysics
Oxidation-Reduction
OXIDOREDUCTASES
Oxidoreductases - metabolism
Oxidoreductases Acting on Sulfur Group Donors - metabolism
OXIDORREDUCTASAS
OXYDOREDUCTASE
Physical chemistry in biology
PIGMENT
PIGMENTOS
PIGMENTS
POLLO
POTENCIAL REDOX
POTENTIEL REDOX
POULET
RADIACION LASER
RAYONNEMENT LASER
REDOX POTENTIAL
sulfite oxidase
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Summary:Laser flash photolysis was used to study the reaction of photoproduced 5-deazariboflavin (dRFH.), lumiflavin (LFH.), and riboflavin (RFH.) semiquinone radicals with the redox centers of purified chicken liver sulfite oxidase. Kinetic studies of the native enzyme with dRFH. yielded a second-order rate constant of 4.0 X 10(8) M-1 s-1 for direct reduction of the heme and a first-order rate constant of 310 s-1 for intramolecular electron transfer from the Mo center to the heme. The reaction with LFH. gave a second-order rate constant of 2.9 X 10(7) M-1 s-1 for heme reduction. Reoxidation of the reduced heme due to intramolecular electron transfer to the Mo center gave a first-order rate constant of 155 s-1. The direction of intramolecular electron transfer using dRFH. and LFH. was independent of the buffer used for the experiment. The different first-order rate constants observed for intramolecular electron transfer using dRFH. and LFH. are proposed to result from chemical differences at the Mo site. Flash photolysis studies with cyanide-inactivated sulfite oxidase using dRFH. and LFH. resulted in second-order reduction of the heme center with rate constants identical with those obtained with the native enzyme, whereas the first-order intramolecular electron-transfer processes seen with the native enzyme were absent. The isolated heme peptide of sulfite oxidase gave only second-order kinetics upon laser photolysis and confirmed that the first-order processes observed with the native enzyme involve the Mo site.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00408a038