Summary: The active center histidines of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system proteins; histidine-containing protein (HPr), enzyme I and enzyme IIAglucose were substituted with a series of amino acids (serine, threonine, tyrosine, cysteine and aspartate and glutamate) with the potential to undergo phosphorylation. The mutants His189Glu Enzyme I, His15Asp HPr and His90Glu enzyme IIAglc retained ability for phosphorylation as indicated by [32P]-phosphoenolpyruvate labelling. As the active center histidines of both enzyme I and enzyme IIAglc undergo phosphorylation of the Ne2 atom, while HPr is phosphorylated at the Nd1 atom, a pattern of successful substitution of glutamates for Ne2 phosphorylations and aspartates for Nd1 phosphorylations emerges. Furthermore, phosphotransfer between acyl residues, P-aspartyl to glutamyl and P-glutamyl to aspartyl was demonstrated with these mutant proteins and enzymes of the phosphoenolpyruvate:sugar phosphotransferase system.