Actin Treadmilling: Difference in Critical Concentrations Explained

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The discussion centers on the differences in critical concentrations for actin polymerization at each end of the filament, attributed to the distinct reactions occurring at the two ends. The addition of T-form actin and removal of D-form actin lead to the same resulting molecule, suggesting a similarity in the reactions. However, the polarity of actin monomers and polymers creates unique characteristics at each end, influencing polymerization and depolymerization kinetics. The presence of GTPase or ATPase in actin monomers also plays a crucial role in these processes. Additionally, actin (de)polymerization is tightly regulated within cells, involving various regulatory proteins such as cofilin, formin, and capping proteins, which manage the dynamics of actin filament assembly and disassembly.
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The critical concentrations at the two ends are different because the reactions taking place are different (addition of a T form and removal of a D form G actin)
but, if you add a T form at any end, the resulting molecule will be the same, and if you remove a D form from any end, the resulting molecule will be the same. so, this reaction is essentially identical at both ends, right? can someone please explain why there is a difference in the critical concentrations here?
 
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Going from memory here. Actin monomers and polymers are polar structures, meaning their structure shows unique characteristics at each 'end.' This polarity gives rise to the difference in polymerization and depolymerization kinetics at either end. Also, don't forget that actin monomers have a GTPase (or ATPase, whichever one actin binds) which effects the polymerization and depolymerization process.

In addition, don't forget that actin (de)polymerization is a highly regulated process. Cells don't just build up and tear down actin all willy nilly. For further reading you should read up the regulation of actin chains due to things like cofilin, formin, capping proteins etc. There are many of them out there. A month ago I could've likely written several pages up for you to read but alas, I have forgotten many of the details now.
 
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