title: UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysine synthetase from Bacillus sphaericus: activation by potassium phosphate.
abstract: During the course of purification of UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysine synthetase, we observed a marked stimulation of the enzymatic activity in the presence of phosphate ions. This activation effect was studied with enzyme purified 979-fold from Bacillus sphaericus. Each salt tested stimulated the activity of the synthetase. The order of activation by different anions was HPO4(2-) greater than Cl- greater than SO4(2-). In every case, the potassium salt gave higher activity than the corresponding sodium salt. The activation in the presence of phosphate was quite pronounced (almost sevenfold with K2HPO4) and occurred at a relatively low concentration. The Ka for K2HPO4 was found to be 3.4 mM and the Hill coefficient was calculated to be 1.0. This would suggest that there is one phosphate-binding site per active centre. The presence of phosphate did not affect either the pH optimum of this enzyme or the optimum concentration of Mg2+ required. The presence of phosphate has little or no effect on the Km of any of the substrates. Thus, it appears that the presence of phosphate changes the enzyme conformation to a catalytically more active form. The activation of this enzyme in the presence of phosphate anion is all the more interesting because phosphate is a product of the reaction catalyzed by this enzyme.
mesh_terms: D001407:Bacillus / Q000201:enzymology*; D002021:Buffers; D004789:Enzyme Activation; D007700:Kinetics; D010453:Peptide Synthases / Q000302:isolation & purification / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D017680:Potassium Compounds
chemical_list: D002021:Buffers; D010710:Phosphates; D017680:Potassium Compounds; C013216:potassium phosphate; D010453:Peptide Synthases; C049448:UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-lysine ligase; D011188:Potassium