Interaction of trans,trans-muconaldehyde with bovine serum albumin

Analysis using sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that incubation of bovine serum albumin (BSA) with 10 microM-1.0 mM trans,trans-muconaldehyde results in the formation of a new band with molecular weight 105 kDa as well as high-molecular-weight material (> 200 kDa), suggesting intermolecular cross-linking of BSA by muconaldehyde. Muconaldehyde-reacted BSA exhibits a decrease in amino groups as measured by the fluorescamine assay. Spectroscopic analysis of the BSA-muconaldehyde incubation mixture shows the formation of two new peaks with absorption maxima at 340 and 475 nm. Gel filtration chromatography on Sephadex G-200 of muconaldehyde-reacted BSA shows elution of a high-molecular-weight fraction and a second fraction which elutes at the elution volume of monomeric unreacted BSA. Both fractions contain material which absorbs light at 280 nm (protein absorption), as well as at 340 and 475 nm, while chromatographed fractions containing unreacted BSA show absorption at 280 nm only. When excited at 340 nm, fractions of muconaldehyde-reacted BSA also exhibit fluorescence emission with a maximum at about 430 nm, whereas excitation at 475 nm does not result in fluorescence emission. Incubation of BSA with the aldehydic muconaldehyde metabolites trans,trans-6-oxo-hexadienoic acid and trans,trans-6-hydroxy-hexa-2,4-dienal or the corresponding diacid trans,trans-muconic acid did not cause any of the effects described above for muconaldehyde, suggesting that the diene-dialdehyde structure of muconaldehyde is a requirement for cross-linking and for the formation of the fluorescing chromophore.