STUDIES ON THE LOW‐MOLECULAR WEIGHT GLYCOPROTEIN GP‐350: MOLECULAR AND IMMUNOLOGICAL HETEROGENEITY

— GP‐350 was isolated from the water soluble cell fraction of bovine brain and liver. The isolated protein preparations were electrophoresed in the presence of SDS in 19% polyacrylamide gels and in the absence or presence of Triton X‐100 and urea in 7.5% polyacrylamide gels. These experiments show that the GP‐350 protein fraction from the different tissues behaves as a class of low‐molecular weight proteins with different intrinsic charges. The majority of the protein bands which were resolved in the presence or absence of Triton X‐100 and urea in 7.5% polyacrylamide gels were not reactive with the antiserum directed against the total GP‐350 protein fraction. Moreover, on gel chromatography in Sephadex G‐50, GP‐350 was fractionated into several peaks. The reactivity with the GP‐350 antiserum in double immunodiffusion was present primarily in the major peak with a molecular weight between 9500 and 11,500; this peak gave three precipitin lines. Furthermore, lipid analysis of GP‐350 has shown that GP‐350 protein preparations from brain contained about 17% (w/w) choloroform‐methanol (2:Insoluble lipids. The lipids were for the major part of neutral type and only trace amounts of glycolipids were detectable. The lipid‐free GP‐350 protein was immunologically identical to the total GP‐350 fraction. On the basis of this heterogeneity in charge, molecular composition and immunological properties we conclude that GP‐350 is a mixture of low‐molecular weight protein and lipid constituents.