An inhibitor of protein synthesis prepared by protease treatment of mouse cerebral cortex cells

A substance was isolated from mouse brain cortical tissue that inhibits both cell division and protein synthesis by cells in culture. The inhibitor was released from cerebral cortex tissue by mild protease treatment. A single exposure of cells to as little as 1.25 μg of the isolated material was sufficient to inhibit BHK-21 cell protein synthesis by 20%. Higher concentrations and continual exposure resulted in 87% reduction in protein synthesis. The inhibition was shown to be independent of amino acid uptake and most effective against primary mouse embryo fibroblasts and neonatal mouse brain cell suspensions. Cells previously adapted to culture or transformed cells derived from the nervous system were less affected by, or refractory to, the inhibitor. The substance was shown to be nondialyzable, relatively resistant to thermal inactivation and the inhibitor activity was not removed by chloroform extraction. Two active fractions were identified by Bio-Gel P-100 chromatography and the protein synthetic inhibitor was removed by affinity chromatography with $\text{Ulex}$$\text{europus}$ agglutinin.