As an alternative to LDLR-mediated uptake and degradation, a LDL particle can bind a single molecule of LPA (apolipoprotein A), forming a Lp(a) lipoprotein particle. Although LPA is synthesized in liver cells, LPA - LDL binding appears to occur primarily extracellularly in vivo, on the hepatocyte surface or in the blood (Lobentanz et al. 1998). Lp(a) particles are relatively long-lived, with a half-life in human plasma of three to four days (Krempler et al. 1980), and the molecular mechanism of their clearance from the blood in vivo remains obscure. Lp(a) particles are of clinical interest because elevated levels of them are correlated with elevated risk of coronary heart disease (reviewed by Marcovina et al. 2003).