Cysteine based novel noncompetitive inhibitors of urease(s)--distinctive inhibition susceptibility of microbial and plant ureases.

Based on the catalysis mechanism of urease, a homologous series of 10 cysteine derivatives (CysDs) was designed and synthesized, and their inhibitory activities were evaluated for microbial ureases (Bacillus pasteurii, BPU, and Proteus mirabilis, PMU) and for a plant urease [jack bean (Cavavalia ensiformis), JBU]. As already described, thiol-compounds might inhibit urease activity by chelating the nickel atoms involved in the catalysis process. In contrast to cysteine, which has been reported to be a very weak urease inhibitor, we verified a potential inhibitory activity of these CysDs. The kinetic data demonstrate that thiol derivatives are more effective than the respective thioether derivatives. Besides, thiol-CysDs had a reduced activity in acidic pH (5.0). Lineweaver-Burk plots indicated that the nature of inhibition was of noncompetitive type for all 10 compounds, with the minimum Ki value of 2 microM for N,N-dimethyl L-cysteine. It is proposed that these classes of compounds are more potent inhibitors of the bacterial ureases, compared with the plant-originated urease. Since microbial urease is directly involved in the infection process of many pathological organisms, this work demonstrates that thiol-CysDs represent a class of new potential urease inhibitors.