Polypeptides are used as building blocks that assemble into polymeric hierarchical architectures with various functionalities based on their amino acid sequences. Chemoenzymatic polymerization using a protease as a catalyst allows us to synthesize peptides with various primary structures in an environmentally benign way. In this work, we performed papain-catalyzed polymerization in the presence of terminal-modifying agents to synthesize peptides modified with a functional group at their N-terminus. Various peptides with a reactive acrylamide group at the N-terminus were synthesized in a one-pot chemoenzymatic reaction with the side groups of the amino acid residues left intact. Acrylamide-modified poly(L-alanine) was used as a macromonomer in a radical copolymerization with N-isopropylacrylamide to give a graft copolymer consisting of poly(L-alanine) side chains.