Multiple site phosphorylation of tyrosine hydroxylase. Differential regulation in situ by a 8-bromo-cAMP and acetylcholine.

Suspension cultures of purified bovine adrenal chromaffin cells incorporated 32P from exogenous 32Pi into a protein of approximately M4 = 60,000 (isolated by discontinuous, sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis). Phosphorylated tyrosine hydroxylase, purified from chromaffin cell supernatants by immunoprecipitation, co-migrated with the Mr = 60,000 band. Tryptic fragments prepared fom either the Mr congruent to 60,000 band or the immunoprecipitated tyrosine hydroxylase band were analyzed after separation with two-dimensional electrophoresis/chromatography. Two distinct 32P-peptides were present in either sample. After a 2-3-min lag period. 32P incorporation into both peptides was relatively linear with time for at least 20 min. In the presence of calcium, exogenous acetylcholine (100 microM) increased 32P incorporation into both of the 32P-labeled tryptic peptides whereas 8-bromo-cAMP (1 mM) increased 32P incorporation into only one of the two. Ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and MnCl2 inhibited the acetylcholine-induced phosphorylation of both tryptic peptides. Thus, tyrosine hydroxylase is phosphorylated in situ at more than one site, and the phosphorylation of these sites is affected differently by acetylcholine and 8-bromo-cAMP. The data imply that kinase activity other than (or in addition to) cAMP-dependent protein kinase activity attends tyrosine hydroxylase in the intact chromaffin cells and that multiple kinase activities may be involved in the short term regulation of catecholamine biosynthesis by afferent activity.