be enhanced the invention also allows targeted delivery of active agents to specifics sites of action the composition of the invention comprises a polypeptide and an active agent covalently attached to the polypeptide preferably the polypeptide is i an oligopeptide ii a homopolymer of one of the twenty naturally occurring amino acids iii a heteropolymer of two or more naturally occurring amino acids iv a homopolymer of a synthetic amino acid v a heteropolymer of two or more synthetic amino acids or vi a heteropolymer of one or more naturally occurring amino acids and one or more synthetic amino acids proteins oligopeptides and polypeptides are polymers of amino acids that have primary secondary and tertiary structures the secondary structure of the protein is the local conformation of the polypeptide chain and consists of helices pleated sheets and turns the protein 39 s amino acid sequence and the structural constraints on the conformations of the chain determine the spatial arrangement of the molecule the folding of the secondary structure and the spatial arrangement of the side chains constitute the tertiary structure proteins fold because of the dynamics associated between neighboring atoms on the protein and solvent molecules the thermodynamics of protein folding and unfolding are defined by the free energy of a particular condition.