Excited States of Flavine Coenzymes‐tv. Kinetics of the Photoreduction of Lumiflavine by Methionine

Abstract

Abstract— Kinetics of fluorescence quenching and photoreduction of lumiflavine by methionine in anaerobic aqueous solution show that the flavine reacts in the excited triplet state at a diffusion controlled rate. Individual rate constants and activation energies are determined for the process.

Riboflavine-catalyzed photooxidative decarboxylation of dihydrophthalates

“…At pH 1.0 about 85% of the flavin fluorescence has been quenched when compared with pH 4.0. If the triplet state is indeed the reactive species in photocatalyzed flavin oxidations, as has been supported by the work of several investigators (Radda and Calvin, 1964;Penzer and Radda, 1967;Byrom and Turnbull, 1967;Penzer and Radda, 1968;Byrom and Turnbull, 1968), then one would expect the observed marked decrease in the rate of the reaction in this p H region. The degree of protonation of the carboxyl groups of the reductants is a second factor which may effect the reaction rate in this pH region.…”

“…When one considers the mechanism for these oxidative decarboxylations, it must be remembered that previous studies have shown that flavin may be reduced by accepting a hydride ion (Suelter and Metzler, 1960;Fox and Tollin, 1966) or alternatively by one electron radical mechanism (Radda and Calvin, 1964;Penzer and Radda, 1967;Byrom and Turnbull, 1967;Penzer and Radda, 1968; Byrom and Turnbull, 1968). In the case of the free acids, a hydridetransfer mechanism would appear to be very attractive.…”

Mechanism of light-induced reduction of biological redox centers by amino acids. A flash photolysis study of flavin photoreduction by EDTA and nitrilotriacetate

“…A Zeiss DMR 10 spectrophotometer was used to record the UV-vis spectra before and after flashing and a Perkin-Elmer °Excited singlet quenching rate constant, determined according to IJI = 1 + fcqsr[Q], with = 5.0 ns (Byrom & Turnbull, 1968;Gordon-Walker et al, 1970).…”