Altered Sensitivity of Aspirin-Acetylated Prostaglandin G/H Synthase-2 to Inhibition by Nonsteroidal Anti-Inflammatory Drugs

Aspirin (ASA) acetylates Ser516 of prostaglandin G/H syn-thase-2 (PGHS-2) resulting in a modified enzyme that converts arachidonic acid to 15(R)-hydroxy-eicosatetraenoic acid [15(R)-HETE]. ASA has pharmacological benefits that may not all be limited to inhibition of prostaglandin synthesis, and this study was initiated to further investigate the properties of ASA-acet-ylated PGHS-2 and of the mutation of Ser516 to methionine, which mimics ASA acetylation. Both the S516M mutant and ASA-acetylated form of PGHS-2 (ASA-PGHS-2) synthesize 15(R)-HETE and have apparent Km values for arachidonic acid within 10-fold of the apparent Km value for untreated PGHS-2. The time courses of turnover-dependent inactivation were sim-ilar for reactions catalyzed by PGHS-2 and ASA-PGHS-2, whereas the PGHS-2(S516M) showed a decrease in both the initial rate of 15-HETE production and rate of enzyme inactiva