Electrophoretic mobilities of brain subcellular particles and binding of γ-aminobutyric acid, acetylcholine, norepinephrine, and 5-hydroxytryptamine

Electrophoretic mobilities of brain synaptosomes and synaptic vesicles and of brain, liver, and kidney mitochondria were determined in a continuous sucrose density gradient. All of the above particles were negatively charged with isoelectric points in the neighborhood of 4. γ-Aminobutyric acid was bound well by the vesicles, synaptosomes, and mitochondria from brain, but not at all by mitochondria from liver or kidney. Acetylcholine was bound to vesicles and synaptosomes but only slightly to the mitochondrial preparations. The binding of 5-hydroxytryptamine to the vesicles, and synaptosomes was much higher than to any of the mitochondrial preparations; while the binding of norepinephrine was much more evenly distributed among the particles. The results suggest that the binding capacities of the particles tested for the above 4 substances are not directly related to the net negative charge, and that the net negative charge on the particles cannot be attributable to that bound form of N-acetylneuraminic acid that can be removed by the action of neuraminidase.