The six aminoterminal residues of pro-apolipoprotein A-1 are removed to generate the mature, lipid-binding form of the protein (APOA1). Studies of tissue culture systems suggest that BMP1 catalyzes this reaction (Chau et al. 2006, 2007). While BMP1 is annotated here as a monomer, its subunit structure is not known, and its 1:1 association with Zn2+ is inferred from its sequence similarity to known metallopeptidases. Tetrameric alpha2-macroglobulin (A2M) at concentrations found in plasma in inflammatory responses inhibits this reaction in vitro, suggesting a possible link between inflammation and perturbation of HDL function (Zhang et al. 2006, Chau et al. 2007).