Effect of temperature on the spectral properties of coenzyme F 420 and related compounds

Abstract

The uv-visible spectra of 7,8-didemethyl-8-hydroxy-5-deazaflavin-5′-phosphoryllactyl glutamate (coenzyme F 420), a naturally occurring 5-deazaflavin derivative, in three different buffers changed with a rise in temperature; the effect on the extinction coefficient at 420 nm ( ε 420) was as follows: In phosphate-buffered solutions at pH < 7.5, the ε 420 increased (at pH 5.0 for a temperature shift from 15 to 60°C, Δε 420 was +87%), but between pH 7.5 and 8, ε 420 changed very little. At pH > 8.0 in phosphate- or borate-buffered solutions, ε 420 decreased slightly. In morpholineethanesulfonic acid (Mes)-buffered F 420 solutions at pH 5 and 5.5, ε 420 changed very little, whereas at pH 6–8, the ε 420 decreased. Absorbance of F 420 at 401 nm in phosphate buffer at pH 5 to 9 was not significantly affected by temperature. Changes in ε 420 due to temperature change corresponded to changes in the p K α of 8-OH of the deazaflavin molecule; studies with adenylated F 420 showed that the 8-OH of F 420 was responsible for these changes. Analysis of data collected with phosphate- and Mes-buffered F 420 solutions showed that for a given temperature shift, if Δp K α for the 8-OH of F 420 does not equal the ΔpH of the buffer, the ε 420 of F 420 would change, and the Δε 420 values can be calculated from derivatives of the van't Hoff and Gibbs equations; the ΔS 0 and ΔH 0 for ionization of the 8-OH of F 420 were found to be 17.04 cal mol −1 oK −1 and −3721.14 cal mol −1, respectively.