SOME PHYSICAL PROPERTIES OF BOVINE ADRENAL MEDULLARY DOPAMINE β-HYDROXYLASE

(1) Dopamine, β-hydroxylase (EC 1.14.2.1) was purified from bovine adrenal medullae according to the method of Foldes , Jeffrey , Preston and Austin (1972). (2) The kinetics, pH optimum and the effect of Cu²⁺ ions on the purified enzyme were found to resemble those of the enzyme isolated by more involved procedures. (3) The sedimentation coefficient (s₂₀) of the homogeneous enzyme in 10 mM-phosphate buffer, pH 7·2, containing 0·1 M-NaCI was found to be 10·24 ± 0·12 (S.E.M. of 10 determinations). (4) The effect of pH on the mol. wt. of the enzyme was investigated and no large deviation was found from the native mol. wt. of 290,000 in the pH range 3·9 to 11·1. (5) The amino acid analysis of dopamine β-hydroxylase is presented, and is contrasted to that of chromogranin A purified from the same chromaffin granule lysate. (6) Treatment with either 8 M-urea or 0·1% (w/v) sodium dodecyl sulphate was found to dissociate the enzyme into three similar, non-active subunits, each of mol. wt. of the order of 100,000.