ABSTRACT
Synaptic vesicles, which have been a paradigm for the fusion of a vesicle with its target membrane, also serve as a model for understanding the formation of a vesicle from its donor membrane. Synaptic vesicles, which are formed and recycled at the periphery of the neuron, contain a highly restricted set of neuronal proteins. Insight into the trafficking of synaptic vesicle proteins has come from studying not only neurons but also neuroendocrine cells, which form synaptic-like microvesicles (SLMVs). Formation and recycling of synaptic vesicles/SLMVs takes place from the early endosome and the plasma membrane. The cytoplasmic machinery of synaptic vesicle/SLMV formation and recycling has been studied by a variety of experimental approaches, in particular using cell-free systems. This has revealed distinct machineries for membrane budding and fission. Budding is mediated by clathrin and clathrin adaptors, whereas fission is mediated by dynamin and its interacting protein SH3p4, a lysophosphatidic acid acyl transferase.
Subject(s)
Synaptic Vesicles/metabolism , Animals , Cytosol/metabolism , Humans , Neurons/metabolism , Synaptic Membranes/metabolismABSTRACT
With reference to a critical study of the relevant literature and to results from their own investigations, the authors emphasize the importance of the semi-essential and non-essential amino acids arginine, histidine, tyrosine, cystine and glutamic acid for the completion of essential amino-acid mixtures destined for parenteral feeding. MADDEN'S assumption that intravenously applied glutamic acid is intolerable was not supported by the authors' experiments in dogs. As evidenced by the increase of blood urea, the glutamic acid-containing amino-acid mixture was well utilizable. When glutamic acid is present, proline and alanine are obviously superfluous in amino-acid mixtures for parenteral feeding, since they are easily formed from glutamic acid by intermediary metabolism.
