Phenylalanine hydroxylase. Correlation of the iron content with activity and the preparation and reconstitution of the apoenzyme.

Phenylalanine hydroxylase requires 1.0 mol of iron/Mr = 50,000 subunit for maximal activity. A direct correlation between iron content and specific activity has been demonstrated through a comparison of enzyme activity and iron bound per subunit for various enzyme preparations and a measurement of the remaining activity upon partial and total removal of the iron by chelation. Apoenzyme has been prepared that can be reactivated by addition of Fe(II) aerobically or of Fe(III) anaerobically. A comparison of the native and reconstituted phenylalanine hydroxylase shows the latter behaves identically upon affinity and Chelex column chromatography as well as precipitation with ammonium sulfate supporting its close similarity to the native enzyme.