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The rates of isotope exchange between the substratelproduct pairs ADPIATP and ATPIP-aspartyl phosphate have been measured for the reaction catalyzed by the lysinesensitive aspartokinase of Escherichia coli B. The ADP * ATP exchange is faster than the ATP @ P-aspartyl phosphate exchange. When the substrate/product pair aspartatel ADP or ADPlATP is varied in a constant ratio, the ATP tipaspartyl phosphate exchange is stimulated at low concentration but suppressed completely at about 12 mM ADP in each case. ADP a ATP exchange is not suppressed by either pair. Potassium ion stimulates both exchange rates but ADP & ATP exchange is stimulated to a greater extent than is ATP * @-asparty phosphate exchange. Chromium (III) ATP is a competitive inhibitor with respect to MgATP and is noncompetitive with respect to aspartate. These data, coupled with our previous work concerning the isolation of enzyme-bound aspartyl phosphate (Manders, W. W., von Dippe, P. J., Horvath, M. L., Smith, V. A., and Smith, W. G. (1969) J. Biol. Chem. 244, 5510-5520) are consistent with an ordered release of products, ADP followed by P-aspartyl phosphate. Addition of aspartate and ATP, on the other hand, appears to be random.
Shaw et al. (Mon,) studied this question.