Peptide bond formation is catalyzed by peptidyl transferase.  The carboxyl  end of the amino acid bound to the tRNA in this reaction and in the P site is uncoupled  from the tRNA and becomes joined by a peptide bond to the amino set of the amino acid connect to the tRNA in the A site. A protein with peptidyl transferase activity has certainly not been isolated.  The reason is now obvious; in E. coli at least, the peptidyl transfers activity is related with part of the 23S rRNA in the vast ribosomal subunit. Alternatively, peptidyl transferase is a ribozyme, a catalytic activity which resides in an RNA molecule.