Bovine retinal angiogenesis factor is a small molecule (molecular mass less than 600)

Two methods were used to extract angiogenic activity from bovine retina. Both methods initially gave rise to nondialyzable (greater than 10,000 Mr) fractions with angiogenic activity. However, after anion exchange chromatography, 20% of the extracts from one of the two methods (method 2) contained a small molecule with angiogenic activity (Mr 300-600). Alcohol treatment of high molecular mass fractions from both methods also released a low molecular mass angiogenic factor (Mr 300-600). No angiogenic activity was left in the nondialyzable residue. The high molecular mass angiogenic fraction obtained by method 1 after DEAE-cellulose chromatography contained a protein immunologically and electrophoretically identical to bovine serum albumin. The low molecular mass retinal angiogenic factor was able to stimulate microvessel endothelial cell proliferation as well as being positive in the chick chorioallantoic membrane test. The presence of a protein carrier system for a small angiogenesis factor is proposed. This would explain discrepancies in the apparent molecular mass of retinal angiogenic factors described previously.