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Isolation of Postsynaptic Densities from Day‐Old Chicken Brain

Abstract: Synaptic plasma membranes from chicken brain were used to isolate a postsynaptic density (PSD) fraction using an aqueous two‐phase polymer system and the detergent n‐octyl glucoside. The protein and glyco‐protein composition and the morphology of the day‐old chicken brain PSD fraction were compared with a PSD fraction isolated from 12‐week‐old chicken brain. The PSD fraction from day‐old chicken brain contained predominantly PSDs although, like the fraction from 12‐week‐old chicken, there was some membrane contamination. The major polypeptides in the day‐old chicken fraction resolved by polyacrylamide gel electrophoresis comigrated with α‐ and β‐tubulin (Mr 57,000 and 55,000) and actin (Mr 45,000). The major PSD polypeptide (mPSDp) of 12‐week‐old chicken forebrain, which has a molecular weight of 52,000 was not a major component in day‐old chicken. A polypeptide of molecular weight 63,000 was also far more prominent in the 12‐week‐old chicken PSD fraction whereas the reverse was true for a polypeptide of 31,000. Day‐old chicken brain PSDs contained at least 14 concanavalin A‐binding glycoproteins of high (>85,000) molecular weight, the two most prominent having molecular weights of 170,000 and 180,000. In contrast to the polypeptide composition, the glycoprotein pattern of day‐old chicken PSDs was very similar to that of the 12‐week‐old bird. Intraperitoneally injected [3H]fucose was incorporated into the glycoproteins of synaptic plasma membranes and PSDs from day‐old chickens. In the synaptic plasma membranes, maximum specific radioactivity relative to homogenate (2.4) was reached after a 24‐h pulse, whereas in the PSDs, relative specific radioactivity continued to rise up to 72 hr after injection to reach a value of 3 times that of the homogenate.