Modification of horse heart cytochrome c with trans-2-hexenal

Horse heart cytochrome c reacting with trans-2-hexenal was used as a simple model of the nonspecific interactions of proteins with 2-alkenals. The reaction mixtures containing relatively high concentrations of the protein and aldehyde were characterized using visible spectrophotometry, fluorescence, and circular dichroism measurement, capillary isoelectric focusing, size-exclusion chromatography, polyacrylamide gel electrophoresis, and mass-spectrometric techniques. The mass-spectrometric data indicate that cytochrome c becomes modified with one or two molecules of hexenal as the major reaction product. The modified species with a correspondingly lowered isoelectric point were detected through capillary isoelectric focusing. The results of proteolytic studies indicate nonspecific modifications. Significant quantities of the oligomeric forms of hexenal-modified protein were also observed electrophoretically.