The thrust of this study is the catalytic properties of PFK amyloid fibrils towards β-lactam hydrolysis. Indeed, Figure demonstrates that PFK amyloid fibrils catalyze hydrolysis of nitrocefin, a widely studied β-lactam surrogate . Nitrocefin undergoes a yellow to red transformation due to hydrolysis of the amide unit in the β-lactam ring. The colorimetric changes can be readily monitored by visible absorbance spectroscopy, and corresponding concentrations of the hydrolyzed reaction product can be determined through calibration. Figure portrays a pronounced increase in the absorbance of hydrolyzed nitrocefin in the presence of PFK amyloid fibrils, reflecting their catalytic activity (solid blue curve). In contrast, monomeric PFK (e.g., the peptide dissolved in a buffered solution not containing KCl) did not induce nitrocefin hydrolysis (broken blue curve in Figure ).