Before revision:  In assembly state, the growth of microtubule includes two processes:  GTP-tubulin binding to the tip of protofilament (PF) and conformational change of PF, during which the penultimate GTP is hydrolyzed and the first tubulin unit that curls out the MT surface is rearranged into MT surface using the energy released from GTP hydrolysis .
After revision:  In assembly state, the growth of microtubule includes two processes: free GTP-tubulin binding to the tip of protofilament (PF) and conformational change of PF, during which the penultimate GTP is hydrolyzed and the first tubulin unit that curls out the MT surface is rearranged into MT surface using the energy released from GTP hydrolysis .