Adenosine deaminase-'like' immunoreactivity in cerebellar Purkinje cells of rat

The localization of adenosine deaminase (ADA) throughout the rat CNS was investigated immunohistochemically with 5 different affinity purified polyclonal antibody preparations against ADA. Except in the cerebellum, identical immunostaining patterns of ADA-immunoreactivity were observed with all 5 antibodies. In the cerebellum, Purkinje cells and presumptive swellings on their axons were immunostained by only one of the 5 antibodies. Preaabsorption with purified ADA abolished immunostaining with all 5 antibodies. Biochemical tests showed that the K_m for substrate, the specific activity of immunoprecipitable enzyme and the isozymic characteristics of cerebellar ADA was not different from ADA in whole brain or several other brain regions examined. The atypical immunohistochemical behavior of cerebellar ADA, despite its biochemical similarity to ADA elsewhere in the brain, suggests that the enzyme in the cerebellum has some unique features which must be taken into account when considering its possible role in regulating the neuromodulatory actions of adenosine in the cerebellar cortex.