Attempts for light microscopical demonstration of guanylate cyclase activity in rat cerebellum

Guanylate cyclase in rat cerebellum was investigated on the light microscopical level with guanylyl imidodiphosphate as substrate. Several attempts for activation of enzymatic activity and delimitation to other enzymes were made by sodium azide, aminophylline, sodium fluoride and dithioerythrole. The localization was similar but less strong compared to adenylate cyclase (Poeggel and Luppa 1984) and differs in behaviour to the above mentioned substances. Nucleotide pyrophosphatases seem to play an unimportant role in guanylyl imidodiphosphate conversion, while alkaline phosphatase is possibly of more importance. A light microscopical demonstration of guanylate cyclase by its enzymatic activity must be considered with caution. Main reasons are the low activity and therefore the great importance of interfering enzymes with high activities.