Adenosine di-, tri- and tetraphosphopyridoxals modify the same lysyl residue at the ATP-binding site in adenylate kinase.

Adenosine diphosphopyridoxal modifies Lys-21 in adenylate kinase which is located in a glycine-rich loop [(1987) J. Biol. Chem. 262, 8257-8261]. We presently report that adenosine tri- and tetraphosphopyridoxals modify the same lysyl residue more rapidly than the diphospho compound does. However, susceptibilities of the Schiff bases between the labels and the lysyl residue to sodium borohydride considerably differ in the modifications with the three reagents. These observations seem to be ascribable to the mobility of the epsilon-amino group of Lys-21 in the active-site region of the enzyme.