title: Low-temperature kinetic measurements of microsecond freeze-hyperquench (MHQ) cytochrome oxidase monitored by UV-visible spectroscopy with a newly designed cuvette.
abstract: A special cuvette was designed to measure optical changes of MHQ (microsecond freeze-hyperquench) powder samples at temperatures below approx. 250 K. Reduced cytochrome c oxidase from Paracoccus denitrificans was reacted with O(2) for 100 micros, frozen as a powder and transferred to the cuvette. Subsequently, cytochrome oxidase was allowed to react further following stepwise increments of the temperature from 100 K up to 250 K while recording spectra between 300 and 700 nm. The temperature was raised only when no further changes in the spectra could be detected. The experiment yielded spectra of the A, P(M), F and O intermediate states. This demonstrated that the catalytic cycle of cytochrome oxidase at low temperature is similar to that at room temperature and so verifies the suitability of this method for the study of enzymes with high catalytic-centre activity.
authors.affiliation: Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC, Delft, The Netherlands.
authors.forename: F G M
authors.initials: FG
authors.lastname: Wiertz
authors.forename: S
authors.initials: S
authors.lastname: de Vries
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003080:Cold Temperature; D003576:Electron Transport Complex IV / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D001426:Bacterial Proteins; D003576:Electron Transport Complex IV