In the previous study, we have shown that Rab3A is dissociated from synaptosomal membranes by Ca2+/calmodulin complex. In this study, we further fractionated the synaptosomal membranes by gradient centrifugation and determined the localization and translocation behavior of Rab3A by Ca2+/calmodulin in the different membrane fractions. Two different membrane pools, light and heavy membrane fractions, were obtained from synaptosomal membranes by self-generating gradient of lodixanol. Rab3A, Rab5, synaptophysin, and synaptobrevin were found to be distributed in the two membrane fractions. When the ratio of Rab3A/synaptophysin was compared in the two membrane fractions, it was found that the value of the ratio in the light fraction was higher than that in the heavy one. To examine whether the dissociation of Rab3A by Ca2+/calmodulin depends on the different fractions of synaptosomal membranes, Ca2+/camodulin was added to the membranes. When the extents of Rab3A dissociation by Ca2+/calmodulin were examined among from unfractionated synaptosomal membrane, fractionated light and heavy membranes, Rab3A was dissociated from all the membrane. The extents of Rab3A dissociation from the two fractionated membrane pools by Ca2+/calmodulin were similar, whereas Rab3A was more easily dissociated by Ca2+/ CAM from unfractionated synaptosomal membranes than from fractionated membranes. The results suggest that additional factor(s) is present on the synaptosomal membrane and involved in the dissociation of Rab3A induced by Ca2+/CaM.
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Park, JB. Dissociation of Rab3A by Ca(2+)/calmodulin from different kinds of synaptosomal membranes. Exp Mol Med 28, 147–152 (1996). https://doi.org/10.1038/emm.1996.23
- synaptic vesicle