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Biochemical Characterization of Annexins I and II Isolated from Pig Nervous Tissue

Abstract: Five proteins having molecular masses of 90, 67, 37, 36, and 32 kDa (p90, p67, p37, p36, and p32, respectively) were identified in the participate fractions of pig brain cortex and pig spinal cord prepared in the presence of 0.2 mM Ca2+ and further purified using a protocol previously described for the purification of calpactins. Proteins p90, p37, and p36 are related to annexins I and II. Annexin II, represented by p90, is found as an heterotetramer, composed of two heavy chains of 36 kDa and two light chains of 11 kDa, and as a monomer of 36 kDa. Protein p37, which differs immunologically from p36, is a monomer and could be related to annexin I. All three proteins are Ca2+‐dependent phospholipid‐ and F‐actin‐binding proteins; they are phosphorylated on a serine and on a tyrosine residue by protein kinases associated with synaptic plasma membranes. Purified p36 monomer and p36 heterotetramer proteins bind to actin at millimolar Ca2+ concentrations. The stoichiometry of p36 binding to F‐actin at saturation is 1:2, corresponding to one tetramer or monomer of calpactin for two actin monomers (KD, 3 × 10−6M). Synaptic plasma membranes supplemented with the monomeric or tetrameric forms of p36 phosphorylate the proteins on a serine residue. The monomer is phosphorylated on a serine residue by a Ca2+‐independent protein kinase, whereas the heterotetramer is phosphorylated on a serine residue and a tyrosine residue by Ca2+‐dependent protein kinases. Antibodies to brain p37 and p36 together with antibodies to lymphocytes lipocortins 1 and 2 were used to follow the distribution of these proteins in nervous tissues. Polypeptides of 37, 34, and 36 kDa cross‐react with these antibodies. Anti‐p37 and antilipocortin 1 cross‐react on the same 37‐ and 34‐kDa polypeptides; anti‐p36 and antilipocortin 2 cross‐react only on the 36‐kDa polypeptides.