IV. Covalent coupling of rat liver phenylalanine hydroxylase.

Rat liver phenylalanine hydroxylase (PheH) was covalently coupled to AH-Sepharose 4B, CH-Sepharose 4B, alginic acid and polygalacturonic acid. The activities of the bound enzyme from the ethanol and ammonium sulfate fractions were studied under a variety of conditions. The ethanol enzyme coupled to AH-Sepharose 4B showed the best thermal stability from 20 degrees to 50 degrees after heating for 15 min. It retained more than 15% of its initial activity after storage at 25 degrees for 9 days. The covalently linked enzymes generally had a broader range of optimal activity from pH 5.8 to 7.5. The presence of a positive or negative microenvironment on the matrix had no effect on the activity of the enzyme coupled to AH- or CH-Sepharose 4B. The failure to obtain hydroxylase activity with enzyme linked to alginic acid or polygalacturonic acid was attributed to the acidic microenvironment of the matrices.