Choline and ethanolamine phosphotransferase activities in glomerular particles isolated from bovine cerebellar cortex

Isolated cerebellar glomeruli provide a relatively homogeneous subcellular fraction, which can be used to study the biochemical events related to chemical transmission within a well-characterized central synapse. Choline and ethanolamine phosphotransferase activities were identified and partially characterized in this nerve ending preparation. Choline phosphotransferase associated with the glomerular particles required Mg2+, while ethanolamine phosphotransferase required Mn2+ for optimal activities. Both enzymes were inhibited by exogenous Ca2+. The apparent Vmax values were 35.9 and 10.0 nmol/hr per mg protein for the choline and ethanolamine phosphotransferases, respectively. The apparent Km value for the CDPcholine substrate was 28.6 microM, and the Km for CDPethanolamine was 8.3 microM. Neither enzyme responded to the various adenine nucleotides, neurotransmitters or neurotransmitter agonists tested. However, exposure of the glomerular particles to cytidine nucleotides inhibited ethanolamine phosphotransferase activity and stimulated choline phosphotransferase activity.