Actin Treadmilling: Difference in Critical Concentrations Explained

[Imperfectus]

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?

 

[Yanick]

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.