Nerve trophic effects: Partial purification from chick embryo brains of proteins that stimulate protein synthesis in cultured newt blastemata

Eighteen-day embryonic chick brain homogenates stimulate the incorporation of 14C-amino acids into proteins of cultured early to medium bud stage newt blastemata. DEAE-cellulose column chromatography of the homogenate yields a fraction which is highly active but unstable. Electrophoresis of the homogenates on “native” polyacrylamide gels (under nondenaturing conditions) yields two regions of activity on the gels when gel fractions are assayed by cutting the gels into segments and placing them directly in the culture medium. The relative mobilities (Rm) of these active regions in 10% polyacrylamide gels are 0.45 ≤ Rm ≤ 0.55 and 0.80 ≤ Rm ≤ 0.90. On 7.5% gels the mobilities increase to 0.60 ≤ Rm ≤ 0.75 and 0.95 ≤ Rm ≤ 1.00. When brain homogenates are further fractionated by two-dimensional electrophoresis, the first dimension on “native” gels and the second dimension on gels containing SDS, only five visibly stained polypeptides can be found in the regions that correspond to the two regions of neurotrophic activity on the native gels. Four of these polypeptides with apparent molecular weights of 47,000, 36,000, 28,000, and 13,500 correspond to the slower migrating region on the native gels. In the faster migrating region, only one peptide of MW 13,500 is visible. We infer that the fast protein and one or more of the slow proteins stimulate protein synthesis in the newt blastemata assay and hence act as neurotrophic factors.