Apolipoprotein H (apo H) has been shown to promote the coagulation of blood platelets by inhibiting thrombomodulin complex and inactivating protein C (Keeling et al.), but can also act as an anticoagulant by binding thrombin and inhibiting its procoagulant effects (Pozzi et al.). Belonging to the lipid-binding apolipoprotein family, within the lipocalin superfamily, apo H is a protein constituent of plasma, with a high affinity for negatively charged phospholipids. The structure of apo H reveals four N-terminal complement control protein (CCP) modules, also known as “sushi” domains, and a distinct fifth C-terminal domain with four antiparallel beta sheets, two alpha-helices, and an extended loop (Schwarzenbacher et al.). Apo H is the main antigen implicated in antiphospholipid syndrome (APS), an autoimmune condition involving pregnancy complications and vascular thrombosis (Brusch). Studies have also reported that Apo H is involved in the progression of atherosclerosis (Harats and George). This protein contains a His-residue tag at the carboxyl end of the polypeptide chain. For consistency and reproducibility across your applications, apolipoprotein H from STEMCELL comes lyophilized with ≥ 93% purity, and is verified by LAL analysis to ensure endotoxin levels are ≤ 1.0 EU/μg protein.