Low density lipoprotein is saturable by pro-oxidant 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.tmin+tmin where the constant, K, is the negative reciprocal of the x-axis intercept of the graphed function, and tmin 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 tmin, while tmin is the minimum time a particular LDL will resist oxidation at a maximum copper concentration.