LOW-DENSITY-LIPOPROTEIN IS SATURABLE BY PROOXIDANT COPPER

The oxidative resistance of low density lipoprotein (LDL) can be experimentally described by the length of time during which no significant lipid peroxidation is observed in a pro-oxidant environment. This period of inhibited oxidation, termed the 'lag phase', is partially due to the radical scavenging reactions of the anti-oxidants contained in the LDL particle. We have shown that the LDL lag time decreases with increasing copper concentration, leveling out at a relatively high copper-to-LDL ratio. This behaviour demonstrates the existence of a finite number of saturable pro-oxidant copper binding sites within the LDL particle. The relationship is described by the equation, lag time = [Cu](-1).K.t(min) + t(min) where the constant, K, is the negative reciprocal of the x-axis intercept of the graphed function, and t(min) is given by the y-axis intercept. By this definition of the constant, K is the amount of copper that will produce a lag time of twice t(min), while t(min) is the minimum time a particular LDL will resist oxidation at a maximum copper concentration.