Albumin associated with purified pig lymphocyte plasma membrane

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Abstract
Plasma membrane preparations purified from pig lymphocytes contained a major polypeptide component with a MW of .apprx. 68,000. This component was identified as pig albumin by the following comparisons with authentic pig serum albumin: co-migration when analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing and non-reducing conditions; identical isoelectric points; similar fingerprints of arginine-containing tryptic peptides; reactivity with anti-(pig albumin) serum. The albumin was bound tightly to the plasma membrane. Biosynthetic labeling of pig lymphocytes under a variety of conditions failed to provide evidence that albumin was synthesized by lymphocytes, suggesting that the plasma membrane-associated albumin was of extraneous origin. Radiolabeled pig serum albumin failed to bind to the plasma-membrane fraction when added before cell disruption. Although lymphocyte plasma membrane preparations from other species possessed a polypeptide with a MW of .apprx. 68,000, this was judged not to be albumin on the basis of electrophoretic mobility under non-reducing conditions; also, no polypeptide was precipitated by anti-albumin sera. Pig lymphocyte plasma membrane preparations apparently possess albumin which, although firmly attached, was probably of extraneous origin. This association appeared not to be common to lymphocytes from other [animal] species.