Finally, to explore whether catalysis by histidyls is general, we performed the hydrolysis experiments in the presence of several histidyl residue containing peptides: His-Asp, His-Lys and His-Gly-Gly. In all case the hydrolysis of imidazole phosphate was catalysed (Figure , His-Asp ¿ and ¯, His-Lys t and v, His-Gly-Gly u and w). The first order rate constant for the hydrolysis of the phosphorylated histidine intermediates (khyd,PHis) being of similar value to that observed for histidine (His-Asp khyd,PHis = 1.7 × 10 -5 s -1 , His-Lys khyd,PHis = 1.7 × 10 -5 s - 1 and His-Gly-Gly khyd,PHis = 2.1 × 10 -5 s -1 , SI Table ).