Characterization and Partial Purification of a Ganglioside‐Associated Mitogen

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Abstract
A nonganglioside factor(s) present in Sigma types II and III mixed bovine brain ganglioside preparations synergizes with suboptimal amounts of serum to induce proliferation specifically in nondividing B103 neuroblastoma cultures. The active substance is nondialyzable and soluble in water as well as in chloroform-methanol mixtures of 1:1-4:1 (vol/vol). It is completely insoluble in ether and acetone at room temperature. Biological activity survives heating to 70.degree. C in the presence of 0.1 M HCl for 1 h as well as boiling at neutral pH. Loss of activity occurs on heating to 70.degree. C for 1 h with 1 M HCl or 1 M NaOH. The activity is insensitive to digestion with neuraminidase, trypsin, pronase and phospholipases A2 and C. The factor cochromatographs with gangliosides on Dowex AG 50W and Sephadex G100 and is partially recovered with GM1 on DEAE-Sepharose, but may be isolated in a ganglioside-free fraction by sequential chromatography on Sephadex LH20 and silicic acid columns. The substance(s) has the properties of a water-soluble proteolipid protein, the amino acid composition being reported. It is not immunologically cross-reactive with antibodies to GM1 ganglioside or the major proteolipid protein of myelin.