Stereospecific and Regioselective Hydrolysis of Cannabinoid Esters by ES46.5K, an Esterase from Mouse Hepatic Microsomes, and Its Differences from Carboxylesterases of Rabbit and Porcine Liver

The properties of ES46.5K, an esterase from mouse hepatic microsomes, were compared with those of carboxylesterases from rabbit and porcine liver. The inhibitory profile with a serine hydrolase inhibitor (bis-p-nitrophenylphosphate) and detergents (sodium dodecylsulfate, Emulgen 911) was different between ES46.5K and the carboxylesterases. Bis-p-nitrophenylphosphate (0.1 mM) markedly inhibited the catalytic activity of the carboxylesterases but not that of ES46.5K. Emulgen 911 (0.05—0.25%) inhibited the catalytic activity of the carboxylesterases, whereas the detergent conversely stimulated that of ES46.5K by 150%. The two carboxylesterases catalyzed the hydrolysis of acetate esters of tetrahydrocannabinol (THC) analogues with different side chain lengths (C1—C5), although ES46.5K showed marginal activity only against the acetate of Δ8-tetrahydrocannabiorcol, a methyl side chain derivative of Δ8-THC. ES46.5K hydrolyzed cannabinoid esters stereospecifically and regioselectively. The esterase hydrolyzed 8α-acetoxy-Δ9-tetrahydrocannabinol (8α-acetoxy-Δ9-THC, 5.62 nmol/min/mg protein), while the enzyme did not hydrolyze 8β-acetoxy-Δ9-THC, 7α-acetoxy-, and 7β-acetoxy-Δ8-THC at all. In contrast, the carboxylesterases from rabbit and porcine liver hydrolyzed 8β-acetoxy-Δ9-THC efficiently but not 8α-acetoxy-Δ9-THC. ES46.5K hydrolyzed side chain acetoxy derivatives of Δ8-THC at the 3′- and 4′-positions, and a methyl ester of 5′-nor-Δ8-THC-4′-oic acid. The enzyme, however, could not hydrolyze methyl esters of Δ8- and Δ9-THC-11-oic acid, while both carboxylesterases hydrolyzed side chain acetoxy derivatives of Δ8-THC and three methyl esters of THC-oic acids. These differences in stereospecificity and regioselectivity between ES46.5K and carboxylesterases suggest that the configurations of important amino acids for the catalytic activities of these enzymes are different from each other