The cyclooxygenase activity of the bifunctional enzyme prostaglandin H2synthase-2 (PGHS-2) is the target of non-steroidal anti-inflammatory drugs. Inhibition of the peroxidase activity of PGHS has been less studied. Using Soret absorption changes, the binding of aromatic hydroxamic acids to the peroxidase site of PGHS-2 was examined to investigate the structural determinants of inhibition. Typical of mammalian peroxidases, the Kdfor benzhydroxamic acid (42 mM) is much greater than that for salicylhydroxamic acid (475 μM). Binding of the hydroxamic acid tepoxalin (25 μM) resulted in only minor Soret changes. However, tepoxalin is an efficient reducing cosubstrate, indicating that it is an alternative electron donor rather than an inhibitor of the peroxidase activity. Aromatic hydrazides are metabolically activated inhibitors of peroxidases. 2-naphthoichydrazide (2-NZH) caused the time- and concentration-dependent inhibition of both PGHS-2 peroxidase and cyclooxygenase activities. H2O2was required for the inactivation of both PGHS-2 activities and indomethacin (which binds at the cyclooxygenase site) did not affect the peroxidase inhibitory potency of 2-NZH. A series of aromatic hydrazides were found to be potent inhibitors of PGHS-2 peroxidase activity with IC50values in the 6-100 μM range for 13 of the 18 hydrazides examined. Selective inhibition of PGHS-2 over myeloperoxidase and horseradish peroxidase isozyme C was increased by certain ring substitutions. In particular, a chloro group para to the hydrazide moiety increased the PGHS-2 selectivity relative to both myeloperoxidase and horseradish peroxidase isozyme C. © 2004 Elsevier Inc. All rights reserved.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below