In an effort to identify a competitive inhibitor that can be used in future
spectroscopic and crystallographic studies and to better understand the in
teraction of a mercaptoacetic acid-thiolester-containing compound with meta
llo-beta-lactamase L1 from Stenotrophomonas maltophilia, inhibition studies
using two thiol-containing compounds were conducted. N-(2'-Mercaptoethyl)-
2-phenylacetamide is a competitive inhibitor of L1 with a K-i of 50 +/- 3 m
u M, and this compound is not a time-dependent inactivator of L1. N-Benzyla
cetyl-D-alanylthioacetic acid is a competitive inhibitor of L1 with a K-i o
f 1.6 +/- 0.3 mu M. Matrix-assisted laser desorption ionization time-of-fli
ght mass spectrometric studies revealed that 2 mol of mercaptoacetate coval
ently bind to L1 upon incubation of the enzyme with N-benzylacetyl-D-alanyl
thioacetic acid; however, this covalently modified enzyme has the same acti
vity as wild-type L1. Last, inhibition studies were used to demonstrate tha
t 4-morpholinoethane-sulfonic acid does not inhibit L1, even at concentrati
ons up to 300 mM. This work identifies two possible competitive inhibitors
which can be used in future structural studies and further demonstrates inh
ibitory heterogeneity among the metallo-beta-lactamases. (C) 1999 Academic
Press.