Preparation of a stable fresh frozen primary lipoprotein[a] (Lp[a]) standard

LP[a] is one of the most atherogenic lipoproteins consisting of an LDL-like core particle and a covalently linked glycoprotein of variable size. Due t o its structural features, its heterogeneity and instability, there are gre at difficulties in standardizing quantitative immunochemical Lp[a] assays. One particular problem is the preparation of a pure primary standard, which is sufficiently stable to be used for value assignment of secondary refere nce material, Here we describe a method to purify Lp[a] to virtual homogene ity, When mixed with glycerol at a ratio of 1:1, the preparation is stable in the deep frozen state for more than 12 months. This: latter material gav e dose-response curves in several immunochemical assays that were parallel to fresh or frozen sera, freshly prepared Lp[a], and other proposed referen ce materials, After determination of the protein content by amino acid anal ysis, it was possible to assign concentrations in molar and mass units to t hese preparations considering the theoretical molecular weights of the part icular apo[a] isoform. Thus we propose to use this procedure for preparatio n of a "gold standard" for Lp[a] assays.