Compartmentation of tyrosine hydroxylase at the nerve ending in rat brain striatum

ABSTRACT

The synthesis of dopamine in rat brain striatal synaptosomes has been studied by two different methods; a radiometric method based on the formation of labelled products from radioactive tyrosine, and an HPLC method based on the measurement of dopamine production. The synaptosomal tyrosine hydroxylase showed different sensitivities to high K[+] depolarization and removal of Ca[2]+ by EGTA when measured by 1]; a liquid chromatographic method [HPLC], or by 2]; a radiochemical assay. The pattern of the time course and extent of activation of the synaptosomal enzyme by dibutyryl-cyclic AMP as measured by the HPLC method was also different from that of radiochemical assay. The differences between the results obtained by these two techniques are interpreted as being consistent with the compartmentation of tyrosine hydroxylase in synaptosomes, i.e. a membrane-bound and a soluble form of the enzyme