Before revision:  In disassembly state, the shortening of microtubule is also described by two processes, the release of GDP-tibulin from the tip of PF and one new tubulin unit curls out from the MT surface.
After revision:  In disassembly state, the shortening of microtubule is also described by two processes, the release of GDP-tibulin from the tip of PF and one new tubulin unit curls out of the MT surface.