Protein covalent modification by biologically active quinones

The avarone/avarol quinone/hydroquinone couple shows considerable antitumor activity. In this work, covalent modification of beta-lactoglobulin by avarone and its derivatives as well as by the synthetic steroidal quinone 2,5(10)-estradiene-1,4,17-trione and its derivatives were studied. The techniques for studying chemical modification of beta-lactoglobulin by quinones were: UV/Vis spectrophotometry, SDS PAGE and isoelectrofocusing. SDS PAGE results suggest that polymerization of the protein Occurs. It Could be seen that the protein of 18 kD gives the bands of 20 kD, 36 kD, 40 kD, 45 kD, 64 kD and 128 kD depending on modification agent. The shift of the pl of the protein (5.4) upon modification toward lower values (from pl 5.0 to 5.3) indicated that lysine amino groups are the principal site of the reaction of beta-lactoglobulin with the quinones.