Scheme 1. Polymerization Reaction of a Y-Looped Bacterial (Escherichia coli) Alkaline Phosphatase (BAP), BAP-Loop-Y, Catalyzed by TL.

(A) BAP-Loop-Y were constructed by substituting the loop domain of the BAP structure (219–221 aa) with a 13-mer Y-Loop (IRINRGPGYAFVT) peptide. TL recognizes and oxidizes phenolic moieties of tyrosine residues on the Y-Loop to form reactive tyrosyl radicals, which then react with each other in a nonenzymatic way to form polymers. (B) Short and sterically hindered Y-Loop made the gap between the BAP-Loop-Y units very small and prevented another activated BAP-Loop-Y reacting at that position.