Detection and characterization of some new basic proteins in chicken postsynaptic densities.

Chicken brain postsynaptic density (PSD) polypeptides, obtained by treating synaptosomes with 0.5% Triton X-100 and then further purified on a sucrose gradient, are demonstrated to contain four basic proteins of 76K (pI greater than 9.2), 58K (pI 8.1-8.8, heterogeneous), 40K (pI 9.0), and 24K (pI 8.9). Nonequilibrium pH gradient-sodium dodecyl sulfate two-dimensional gels further reveal six more basic proteins with pI values higher than 9.2: 76K, 52K, 47K, 45K, 36K, and 34K. These basic proteins are a major part of the total chicken PSD polypeptides appearing on the gels. Some of these basic proteins (58K, 52K, 47K, 36K, 24K, and two at 76K) are distinguishable from those of brain mitochondria, the major contaminant. The 40K and 34K proteins may be common mitochondrial polypeptides. The 45K protein is probably a mitochondrial contaminant. A number of proteins including 76K (synapsin I-like protein) and 58K, along with some other minor ones, can be phosphorylated by endogenous protein kinase(s) in the presence of Ca2+, Mg2+, and [gamma-32P]ATP. No PSD basic proteins bind Ca2+.