The secreted recombinant pro form of rat PCSK9 comprises 672 amino acids and predicts a molecular mass of 72.8 kDa. As a result of glycosylation and proteolytic digestion, rat PCSK9 migrates as doublet with apparent molecular mass of 20 kDa and 62 kDa corresponding to the pro domain and mature form respectively in SDS-PAGE under reducing conditions.