D2 is a nervous-specific membrane protein enriched in fractions of synaptosomal membranes from rat brain. Recently, an immunochemical relationship between D2 and the chick cell adhesion molecule (CAM) has been demonstrated. There is reason to believe that D2 is involved in adhesion phenomena between neurites. The purpose of the present study was to purify and further characterize the D2 protein from rat brain. In the developed purification procedure synaptosomal membranes from rat brains were prepared and solubilized by means of non-ionic detergent. The subsequent purification steps were hydroxylapatite chromatography, wheat germ lectin affinity chromatography, gel filtration, and lysine affinity chromatography. The purified D2 was found to be enriched 240 times compared with the starting brain homogenate and 120 times compared with the synaptosomal membrane fraction. The recovery of D2 was 26% when the amount of D2 in the synaptosomal membrane fraction was set to 100%. The purified D2 antigen was used for production of monospecific rabbit antisera, and it was found to be composed of two polypeptides of apparent molecular weights 130,000 and 150,000, respectively.

The initial changes in Gc-globulin can be explained by increased release of actin from injured muscle tissue. Subsequently Gc-globulin displays characteristics of a so-called positive acute phase reactant, supporting previous in vitro studies, and clinical studies after minor surgery. In spite of genetic linkage and structural homology Gc-globulin and albumin are regulated differently after surgical trauma.

Many antibody preparations exhibit proteolytic activity due to the presence of plasmin. In crossed immunoelectrophoresis at pH 8.6 this enzyme can degrade certain proteins during electrophoresis in the antibody-containing gel, resulting in artefacts in the form of extra precipitation arcs of congruent shape. The degradation behaviour of spectrin, a major protein of human erythrocyte membranes, was investigated. The artefact could be completely abolished by the addition of protease inhibitors, e.g. aprotinin and soya bean trypsin inhibitor, to the antibody preparations. 0. J. Bjerrum, M . D., The Protein Laboratory, Sigurdsgade 34, DK-2200 COpenhagen, Denmark SUPPI. 2, 81-88, 1975.

Lectins were included in the first dimension gel in crossed immunoelectrophoresis of human serum proteins. Con A resulted in a retardation of most glycoproteins during the first electrophoresis and heterogeneous forms of individual glycoproteins could be detected. Ulex europeus lectin gave most of the proteins a higher migration velocity. Pokeweed mitogen did not interact with serum glycoproteins, but it did with serum lipoproteins. The method allows a close study of interacting components, determination of binding specificities, and detection of minor interacting components, including heterogeneous molecular forms.