EFFECT OF TEMPERATURE ON THE SPECTRAL PROPERTIES OF COENZYME-F(420) AND RELATED-COMPOUNDS

The uv-visible spectra of 7,8-didemethyl-8-hydroxy-5-deazaflavin-5′-phosphoryllactyl glutamate (coenzyme F420), 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 (ε420) was as follows: In phosphate-buffered solutions at pH < 7.5, the ε420 increased (at pH 5.0 for a temperature shift from 15 to 60°C, Δε420 was +87%), but between pH 7.5 and 8, ε420 changed very little. At pH > 8.0 in phosphate- or borate-buffered solutions, ε420 decreased slightly. In morpholineethanesulfonic acid (Mes)-buffered F420 solutions at pH 5 and 5.5, ε420 changed very little, whereas at pH 6-8, the ε420 decreased. Absorbance of F420 at 401 nm in phosphate buffer at pH 5 to 9 was not significantly affected by temperature. Changes in ε420 due to temperature change corresponded to changes in the pKα of 8-OH of the deazaflavin molecule; studies with adenylated F420 showed that the 8-OH of F420 was responsible for these changes. Analysis of data collected with phosphate- and Mes-buffered F420 solutions showed that for a given temperature shift, if ΔpKα for the 8-OH of F420 does not equal the ΔpH of the buffer, the ε420 of F420 would change, and the Δε420 values can be calculated from derivatives of the van't Hoff and Gibbs equations; the ΔS0 and ΔH0 for ionization of the 8-OH of F420 were found to be 17.04 cal mol-1 oK-1 and -3721.14 cal mol-1, respectively. © 1992.