Characterization of Annexins in Mammalian Brain

Three annexins‐p68, endonexin, and p32‐have been isolated from porcine brain using their calcium‐dependent affinity for membranes. Large amounts (20‐50 mg/kg of tissue) of p68 and p32 can be isolated from cerebrum and cerebellum. The p68 is present as up to 0.3% of total porcine brain protein. The p68 and p32 from porcine brain bind to phosphatidic acid (half‐maximal binding at 6 and 34 μM free calcium, respectively) and to phosphatidylserine (8 and 34 μM, respectively). They do not bind to phosphatidylcholine at calcium concentrations up to 1 mM. Two other major proteins (M r 180,000 and M r 76,000) were isolated with the annexins in a calcium‐dependent manner but do not bind to phospholipids. The 180‐kilodalton protein is the heavy chain of clathrin. From immunohistochemical studies, p68 is strongly associated with the plasma membranes of Purkinje cell bodies and dendrites in porcine cerebellum. It is also an intracellular component of Purkinje cells localized to perinuclear structures. Staining of axons in the white matter and granule cell layer was also seen. In contrast, p32 is completely absent from Purkinje cells and their dendrites; it is predominantly located in the molecular layer and in white matter of the cerebellar folds. The distribution of p32 may be consistent with a predominantly glial localization.