Kinetics of inhibition and molecular asymmetry in pigeonpea (Cajanus cajan) urease.
Urease from seeds of pigeonpea showed a time-dependent and irreversible inactivation at very low concentrations of heavy metal ions. Concentration of Cu(2+), Hg(2+) and Ag(+) required for 50% inactivation, on 10 min of incubation, were found to be 2.2 x 10(-6), 2.9 x 10(-8) and 6.3 x 10(-12) M, respectively. The kinetics of inactivation with each of these metal ions was found to be biphasic, with half of the activity being lost in a fast phase and remaining in a slow phase. Acetohydroxamate (AHA) inhibits pigeonpea urease competitively and reversibly with a K(i) of 0.041 mM at pH 7.3. This inhibition was found to be pH dependent. A reversible and time-dependent inhibition was observed with AHA. AHA inhibition revealed biphasic kinetics as observed with the heavy metal ions. Pigeonpea urease was also inhibited by fluoride ions competitively with a K(i) value of 1.23 mM. These inhibition studies suggest the possible interaction of these inhibitors with active site thiol groups and Ni (II) ion. A mechanism has been proposed for each of these inhibitors and compared with inhibition studies reported for other ureases.
School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi, India.
Punit K
PK
Srivastava
Arvind M
AM
Kayastha
Medicherla V
MV
Jagannadham
D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007887:Fabaceae / Q000201:enzymology*; D005459:Fluorides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006877:Hydroxamic Acids / Q000494:pharmacology; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D019216:Metals, Heavy / Q000494:pharmacology; D012639:Seeds / Q000201:enzymology; D013997:Time Factors; D014510:Urease / Q000737:chemistry* / Q000378:metabolism*
D004791:Enzyme Inhibitors; D006877:Hydroxamic Acids; D007477:Ions; D019216:Metals, Heavy; C006358:acetohydroxamic acid; D014510:Urease; D005459:Fluorides