Synaptic vesicle ceramide kinase. A calcium-stimulated lipid kinase that co-purifies with brain synaptic vesicles

Much current work on the mechanism of neurosecretion has focused on proteins specific to neural secretory vesicles (synaptic vesicles). We report a calcium-stimulated lipid kinase that co-purifies with rat brain synaptic vesicles. This enzyme activity is found only in membrane fractions that contain synaptic vesicle markers. Based on identification of the lipid product as ceramide 1-phosphate and on the finding that ceramide kinase activity co-purifies with synaptic vesicles, the enzyme is proposed to be a ceramide kinase. Kinase activity is stimulated by micromolar concentrations of calcium. Calcium increases the apparent Vmax of the reaction with little effect on the Km for ceramide. The vesicular localization of this enzyme, the requirement for ATP, and the stimulation of enzyme activity by micromolar calcium suggest that ceramide phosphorylation may be associated with neurotransmitter release.