LIPOSOME EFFECT ON THE CYTOCHROME C-CATALYZED PEROXIDATION OF CARBONYL SUBSTRATES TO TRIPLET SPECIES

Cytochrome c exhibits peroxidase activity on diphenylacetaldehyde (DPA A) and 3-methylacetoacetone (MAA), which is greatly affected by the pr esence and nature of charged liposome or micelle interfaces interactin g with the enzyme. The ferricytochrome c reaction with DPAA is acceler ated when the enzyme is attached to negatively charged interfaces. Wha tever the medium, bulk solution or negatively charged dicetylphosphate (DCP), phosphatidyl coline/phosphatidylethanolamine/cardiolipin (PC/P E/CL) liposomes, this chemiluminescent reaction is accompanied by redu ction of cytochrome c to its ferrous form. In turn, MAA is oxidized by cytochrome c exclusively when bound to DCP liposomes. Contrary to DPA A oxidation, the MAA reaction is followed by bleaching of cytochrome c , reflecting damage to the hemeprotein chromophore. The cytochrome-c-c atalyzed oxidation of either DPAA or MAA leads to concomitant disappea rance of the enzyme charge transfer absorption band at 695 nm. This su ggests that the peroxidase activity of cytochrome c involves substrate -induced loss of the methionine ligand at the iron sixth coordination position, which is favored by interaction of cytochrome c with negativ ely charged interfaces. Accordingly, a decrease and blue shift of the charge transfer band could be observed in cytochrome-c-containing nega tively charged DCP, PC/PE/CL liposomes or lysophosphatidylethanolamine micelles in the presence of DPAA or MAA.