title: Inhibition of camel lens zeta-crystallin by aspirin and aspirin-like analgesics.
abstract: Camel lens zeta-crystallin was reversibly inhibited to various degrees by aspirin (acetyl salicylic acid) and the aspirin-like analgesics: paracetamol (acetaminophen) and ibuprofen (2-(4-isobutyl phenyl)-propionic acid). Among these, aspirin was the most potent inhibitor, causing nearly complete inhibition in a dose-dependent, but time-independent manner. Analysis of inhibition kinetics revealed that aspirin was uncompetitive inhibitor (K(i) 0.64 mM) with respect to NADPH and non-competitive inhibitor (K(i) 1.6 mM) with respect to the substrate, 9,10-phenanthrenequinone (PQ). Multiple-inhibition analysis showed that aspirin and pyridoxal 5' phosphate (PAL-P), a lysine specific reagent, simultaneously bound to a critical lysine residue located towards the NADPH binding region. Consistent with this, NADPH was able to substantially protect zeta-crystallin against aspirin, whereas PQ did not provide any protection. The results suggested that an essential lysine residue was the locus of aspirin binding. The inhibition of zeta-crystallin by aspirin and aspirin-like analgesics was reversible thus eliminating acetylation as a mechanism for inhibition. Reversible binding of aspirin to this lysine may cause steric hindrance resulting in uncompetitive inhibition with respect to NADPH.
authors.affiliation: Department of Biochemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia.
authors.forename: Mohammad D
authors.initials: MD
authors.lastname: Bazzi
authors.forename: Nayyar
authors.initials: N
authors.lastname: Rabbani
authors.forename: Ali S
authors.initials: AS
authors.lastname: Duhaiman
mesh_terms: D000082:Acetaminophen / Q000494:pharmacology; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001241:Aspirin / Q000494:pharmacology*; D001665:Binding Sites; D001667:Binding, Competitive; D002162:Camelus; D003459:Crystallins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D007052:Ibuprofen / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008239:Lysine / Q000737:chemistry; D009249:NADP / Q000378:metabolism; D010616:Phenanthrenes / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000494:pharmacology
chemical_list: D000700:Analgesics; D003459:Crystallins; D010616:Phenanthrenes; D000082:Acetaminophen; C005399:9,10-phenanthrenequinone; D009249:NADP; D011732:Pyridoxal Phosphate; D008239:Lysine; D001241:Aspirin; D007052:Ibuprofen