On a basic 31 kDa muscle membrane protein in cattle and pig, presumably equivalent to the class II antigen associated p31 molecule.

In a recent paper we gave evidence by two-dimensional electrophoresis that, in man, the class II antigen associated glycoprotein p31 (also called Ii, In, M1, DR gamma, XM1) is expressed not only in the membranes of B lymphocytes but also in those of muscle, liver and brain. It can therefore be assumed that the p31 is not really associated with the human class II antigens but is a ubiquitous molecule. Here we demonstrate for the first time that the muscle membranes of cattle and pig contain corresponding polypeptides, with a molecular weight of about 31 kDa and an isoelectric point around 7.5, which comigrate in two-dimensional electrophoresis with p31 derived from the human muscle. Thus, in cattle and pig too, these proteins seem to be equivalent to the class II antigen associated p31, showing a tissue distribution wider than observed up to now. The molecules can be concentrated by ion-exchange chromatography.