Isolation of Postsynaptic Densities from Day‐Old Chicken Brain

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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 glycoprotein composition and the morphology of the day-old chicken brain PSD fraction were compared with a PSD fraction isolaged from 12-week-old chicken brain. The PSD fraction from day-old chicken brain contained predominately PSDs although, like the fraction from 12-week-old chicken, there was some membrane contamination. The major polypeptides in the in the day-old chicken fraction resolved by polyacrylamide gel electrophoresis comigrated with .alpha.-and .beta.-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.