We examined whether the histidyl peptides would also catalyse other substrates. We examined the phosphorylation of glycerate as 2-phosphoglycerate is a precursor in the formation of phosphoenolpyruvate which is biology's highest-energy phosphate. The physicochemical orthophosphate cycle in the presence of the histidyl catalysts histidine and His-Lys was performed starting from a solution of 20 mM sodium phosphate, 230 mM potassium cyanate and 100 M imidazole with 500 mM glycerol nucleophile, in the presence and absence of 100 mM histidyl catalyst at pH 7.3 and 22 °C. In the first cycle no catalysis of phosphorylated glycerate was observed (Figure ). However, in the second and third cycle catalysis was observed after sufficient imidazole phosphate and phosphorylated histidine had accumulated. Thus confirming the generality of this system.