1. 1. Phosphorylcholine-reactive protein (PRP) affinity-purified from channel catfish (Ictalurus punctatus) serum on phosphorylcholine-Sepharose, eluted from Bio-Gel A-5M as a 94.6 ± 2.4 kDa protein when the gel filtration column buffer (Tris-saline) contained 25 mM ethylenediaminetetraacetic acid (EDTA). 2. 2. PRP chelated with EDTA immediately after affinity purification and gel-filtered in Tris-saline-EDTA, eluted as a 75.5 ± 2.67 kDa protein referred to as fast-PRP (F-PRP) 3. 3. PRP and F-PRP were identical on SDS-PAGE. Both resolved as a broad band of protein (ca 86-100 kDa) on non-reducing gels or as a ca 100 kDa protein after reduction with 2-mercaptoethanol (2-ME). 4. 4. After gel-filtration in Tris-saline-EDTA, nearly complete reduction of 100 kDa PRP was achieved on SDS-PAGE. However, the protein regained its resistance to reduction upon storage at -60°C. 5. 5. SDS-PAGE and native PAGE also revealed that during storage, PRP and F-PRP combined to form 3 different aggregates referred to as aggregated-PRP (aggPRP). These aggregates are readily dissociated in the presence of 2-ME, suggesting a covalent interaction between adjacent pentamers comprising decameric aggPRPs. 6. 6. PRP, F-PRP, and aggPRP have similar amino acid compositions. © 1992.