IRON RELEASED FROM TRANSFERRIN AT ACIDIC PH CAN CATALYZE THE OXIDATION OF LOW-DENSITY-LIPOPROTEIN

Low density lipoprotein (LDL) oxidation within the arterial wall may c ontribute to the disease of atherosclerosis. We have investigated the conditions under which transferrin (the major iron-carrying protein in plasma) may release iron ions to catalyse the oxidation of LDL. Trans ferrin that had been incubated at pH 5.5 released approximately 10% of its bound iron in 24 h, as measured by ultrafiltration and atomic abs orption spectroscopy. Furthermore, transferrin co-incubated with LDL a nd L-cysteine at pH 5.5 resulted in the oxidation of the LDL as measur ed by thiobarbituric acid-reactive substances and electrophoretic mobi lity. This effect was observed at transferrin concentrations as low as 40% of its average plasma concentration. The release of iron from tra nsferrin in atherosclerotic lesions due to a localised acidic pH may h elp to explain why LDL oxidation occurs in these lesions.