STRIATAL DIHYDROXYPHENYLALANINE DECARBOXYLASE AND TYROSINE-HYDROXYLASE PROTEIN IN IDIOPATHIC PARKINSONS-DISEASE AND DOMINANTLY INHERITED OLIVOPONTOCEREBELLAR ATROPHY

We measured the levels of dopamine, tyrosine hydroxylase (TH) protein, and dihydroxyphenylalanine (DOPA) decarboxylase (DDC) protein in the striatum of 10 patients with idiopathic Parkinson's disease (PD) and 2 3 patients with dominantly inherited olivopontocerebellar atrophy (OPC A). The levels of dopamine were markedly reduced (2% of control) in th e striatum of the patients with PD, whereas striatal dopamine in the p atients with OPCA ranged from normal (>60% of control) to moderately r educed (20-60% of control) to severely depleted (<20% of control). Bot h TH and DDC protein levels were significantly lower than those of the controls in the striatum of all of the patients with PD and in the su bgroup of patients with OPCA having severely depleted dopamine. In con tradistinction, TH but not DDC protein levels were reduced in those pa tients with OPCA having moderately reduced dopamine levels. This sugge sts that in the early stage of nigrostriatal dopamine neurone degenera tion, DDC levels may be less susceptible to neurodegenerative influenc es than is TH synthesis or, alternatively, DDC synthesis may be more a ggressively upregulated. Unexpectedly, from the blot immunolabeling an alysis an additional DDC-immunoreactive band of slightly lower apparen t molecular mass was detected in two of the patients with PD and in 12 of the patients with OPCA. This additional DDC band, which was not pr esent in any of the control subjects, may reflect posttranslational mo dification(s) of DDC related to the neurodegenerative process.