Abstract
Isolated synaptosomes from guinea pig brain homogenates incorporated choline- 14C when incubated either in a medium with an external energy source or in one containing only Tris buffer. The incorporation was divisible into three fractions: total, TCA-insoluble, and chloroform-soluble. Incorporation of choline- 14C into the chloroform-soluble fraction was affected by the cations in the incubating medium: Na, K and Mg were inhibitory. Conversely, incorporation of acetylcholine- 14C into the chloroform-soluble fraction did not occur in the presence or absence of these ions. When the isolated synaptosomes were labeled with choline- 14C and the subsynaptosomal localization of the choline determined, the synaptic vesicle fraction contained the highest choline- 14C activity. When the various subsynaptosomal fractions were isolated and incubated with choline- 14C, the isolated synaptic vesicles incorporated choline- 14C to the greatest extent; extremely high incorporation occurred in both the “total” and chloroform-soluble fractions.
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