INTRASYNAPTOSOMAL CONVERSION OF TYROSINE TO DOPAMINE AS AN INDEX OF BRAIN CATECHOLAMINE BIOSYNTHETIC CAPACITY

—The potential for intrasynaptosomal conversion of tyrosine to dopamine was evaluated in the cell bodies (substantia nigra) and nerve terminals (caudate-putamen) of the nigral-striatal dopaminergic pathway. The conversion technique involves measurement of 14CO2 evolved from carboxyl-labelled tyrosin...
Ausführliche Beschreibung

—The potential for intrasynaptosomal conversion of tyrosine to dopamine was evaluated in the cell bodies (substantia nigra) and nerve terminals (caudate-putamen) of the nigral-striatal dopaminergic pathway. The conversion technique involves measurement of 14CO2 evolved from carboxyl-labelled tyrosine in the absence of both exogenous pteridine cofactor and DOPA decarboxylase. Evaluation of apparent Km values for tyrosine uptake and conversion and observed maximal velocities suggest that conversion is not limited by movement of substrate into the synaptosomes. The results, based on brain regional and subcellular distribution, are consistent with the localization of conversion in nerve endings and suggest a rapid and reliable measure for catecholamine biosynthetic capacity when structural integrity of the nerve ending is maintained. Ausführliche Beschreibung