Covalent Affinity Labeling of Brain Catecholamine‐Absorbing Proteins Using a High‐Specific‐Activity Substituted Tetrahydronaphthalene

The recently described catecholamine-absorbing proteins (CATNAPs) are expressed within the CNS and have been shown to participate in neurochemical processes involving dopamine and several structurally related catecholamines. Specifically, CATNAPs have been implicated in participating directly in oxidative mechanisms involving reactive species (such as free radicals) derived from these compounds. Toxic free radicals generated from endogenous catecholamines have been identified as a major cause of neuronal tissue injury and are implicated in several disease processes. CATNAPs were first identified by their ability to react covalently with tritiated dopaminergic compounds, incorporating low levels of radioactivity under appropriate reaction conditions. The biochemical characterization of CATNAPs has until now been hampered by the lack of a suitable high-specific-activity probe to allow the rapid detection of these proteins. We describe here the synthesis and labeling characteristics of a high-specific-activity substituted tetrahydronaphthalene derivative (6-hydroxy-[125I]iodo-[N-(N-2',4'- dinitrophenyl)aminopropyl]-2-amino-1,2,3,4-tetrahydronaphthalene), which covalently incorporates into CATNAPs with the same tissue distribution, molecular weight patterns, and pharmacology as observed for the previously studied tritiated catecholamines. This compound greatly enhances the detection of CATNAPs and will facilitate further biochemical characterization of these proteins.