Molecular Pharmacology, Vol 7, 136-146, Copyright © 1971 by the American Society for Pharmacology and Experimental Therapeutics

Different Molecular Forms of Bovine Adrenal Tyrosine Hydroxylase

¹ Department of Pharmacology, New York University School of Medicine, New York, New York 10016

The sedimentation coefficients of native and trypsin-treated bovine adrenal tyrosine hydroxylase were determined by sucrose density gradient centrifugation and compared with protein standards whose sedimentation coefficients were known. Native tyrosine hydroxylase was found to have a sedimentation coefficient of 9.20 S^0.725_20.w, and that of trypsin-treated tyrosine hydroxylase was 3.45 S^0.725_20.w. Using this information and known molecular weights of the protein standards, it was possible to make a rough estimation of time molecular weights of the two forms of the enzyme.

Sephadex gel filtration was also used to estimate the molecular weights of the two forms of tyrosine hydroxylase. A Stokes radius of 23.7 A and a frictional ratio of 1.12 were also determined for trypsin-treated tyrosine hydroxylase by gel filtration; these determinations were not possible for the native form of the enzyme because of the presence of urea, which was necessary to avoid time aggregation of tyrosine hydroxylase.

The sedimentation coefficients and the Stokes radius of trypsin-treated tyrosine hydroxylase were used to calculate the molecular weight of this enzyme, which was found to be 34,000. It was also determined that the molecular weight of native tyrosine hydroxylase is approximately 4 times that of time trypsin-treated enzyme. These results indicate that trypsin-treated tyrosine hydroxylase is only a fragment of the native form.