Covalent coupling of rat liver phenylalanine hydroxylase

Optimal conditions have been determined for the coupling of rat liver phenylalanine hydroxylase (Phe H) to cyanogen bromide-Sepharose 4B. When 8 mg of ligand was reacted with 100 mg of matrix, 20 to 30 percent of the initial enzyme activity was covalently bound along with 90 percent of the protein. The coupled enzyme showed greater thermal stability from 40 degrees to 60 degrees, a broader base of optimal pH activity from 5.8 to 10.0, more resistance to proteolysis and less inhibition by various inhibitors. The uncoupled enzyme exhibited greater storage stability at 25 degrees after 24 hr and at 0 degrees after 18 days. Alteration of the microenvironment by introduction of sulfhydryl groups or of carriers having positive or negative charges had variable effects on the hydroxylase activity.