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Ultrastructural Aspects of Exocytosis
| Content Provider | Scilit |
|---|---|
| Author | Plattner, Helmut |
| Copyright Year | 2019 |
| Description | Book Name: Membrane Fusion |
| Abstract | Evidence is accumulating that the organization of membranes at sites of exocytotic membrane fusion might be principally similar in quite different systems. This includes the presence of both membrane-integrated proteins [assumed to correspond mainly to the membrane-intercalated particles (MIP) seen after freeze-fracturing] and membrane-associated proteins. Among others, the presence of $Ca^{2+}$-dependent enzymes [(phospho-) protein phosphatase/kinase] or of $Ca^{2+}$-sensitivity conferring constituents (including calmodulin) must be taken into consideration. Some of these elements might contribute to “membrane-connecting materials,” while the molecular equivalent of MIP is not yet known. Altogether a probable regulatory function of these proteins for exocytotic membrane fusion is quite likely. This is supported by the fact, that, at least in Paramecium cells, the absence of these structural elements from fusogenic sites in different mutations or in their phenocopies always entails the incapability to perform exocytotic membrane fusion. However, the occurrence of highly regular MIP aggregates at fusion sites, as they occur in Paramecium, is the exception, rather than the rule. Thus, it remains to be seen whether the existence of preformed exocytotic fusion sites is a general phenomenon. In all cases analyzed with reliable ultrastructural methods, exocytotic membrane fusion operates without previous restructuring of the membranes involved; it is always a focal event (with an “instability focus” of a diameter in the 10-nm range) and it operates without the formation of a lipidic diaphragm. Wherever preparative artifacts had been reliably excluded, no exceptions from these rules have been observed. This holds even for widely different systems, such as protozoa, nerve terminals, oocytes, mast cells, adrenal chromaffin cells, and so forth. For further structural analyses it will be challenging to identify in situ the different structural components occurring at sites involved in exocytosis. References for all these aspects will be given throughout the text. |
| Related Links | https://content.taylorfrancis.com/books/download?dac=C2006-0-06515-7&isbn=9780367811525&doi=10.1201/9780367811525-25&format=pdf |
| Ending Page | 598 |
| Page Count | 28 |
| Starting Page | 571 |
| DOI | 10.1201/9780367811525-25 |
| Language | English |
| Publisher | Informa UK Limited |
| Publisher Date | 2019-11-14 |
| Access Restriction | Open |
| Subject Keyword | Book Name: Membrane Fusion Microbiology Function Proteins Membrane Fusion Ultrastructural Different Systems Exocytotic Membrane |
| Content Type | Text |
| Resource Type | Chapter |
