Figure indicates that PFR also catalyzes nitrocefin hydrolysis, albeit variability in both catalytic efficiencies and mechanisms are apparent, illuminating key parameters accounting for the catalytic activity of PFK amyloid fibrils. Like PFK, PFR also formed cationic fibrils but displayed a significantly different catalytic profile. Specifically, PFR fibrils gave rise to a hyperbolic catalytic curve, reflecting a MM-like mechanism (Hill coefficient equals 1.6), less pronounced substrate binding (Kh=160 µM), and lower maximal reaction rate (Vmax = 41 µM/h), primarily linked to the low turnover constant (Kcat of 0.05 s -1 ) (Figure ). The low Kh and Kcat values account for relatively high stability of the fibril-substrate complex, which constitutes a barrier to progression of the hydrolysis reaction and overall lower catalytic efficiency. Overall, the comparative catalytic analysis in Figure underscores the key role of the lysine residues in the catalytic mechanism of PFK amyloid fibrils.