ATP-dependent inactivation and slow binding inhibition of Salmonella typhimurium D-alanine:D-alanine ligase (ADP) by (aminoalkyl)phosphinate and aminophosphonate analogues of D-alanine

Abstract

In Salmonella typhimurium, D-alanine:D-alanine ligase (ADP) (EC 6.3.2.4) is the second enzyme in the three enzyme D-alanine branch pathway of peptidoglycan biosynthesis. The interaction of this enzyme with a possible transition-state analogue, the (aminoalkyl)phosphinate D-3-[(1-aminoethyl)phosphinyl]-2-heptylpropionic acid [Parsons et al. (1987) Abstracts of Papers, 193rd National Meeting of the American Chemical Society, Denver, CO, MEDI 63, American Chemical Society, Washington, DC], has been studied. This compound is a potent active site directed inhibitor and is competitive with D-alanine (Ki = 1.2 microM); it exhibits time-dependent inhibition in the presence of ATP. Kinetic analysis revealed a rapid onset of steady-state inhibition (kon = 1.35 X 10(4) M-1 s-1) followed by slow dissociation of inhibitory complex(es) with a half-life of 8.2 h. The inhibitory complex was shown to consist of E...I...ATP in equilibrium with E...I, Pi, and ADP. Similar time-dependent inhibition was also observed with D-(1-aminoethyl)phosphonic acid (D-Ala-P) (Ki = 0.5 mM; kon = 27 M-1 s-1; t1/2 for regain = 1.73 min) but not with D-(1-aminoethyl)phosphinic acid, which behaved as a simple competitive inhibitor (Ki = 0.4 mM). The mechanism of inhibition is discussed in the light of the precedents of glutamine synthase inhibition by methionine sulfoximine and phosphinothricin.