Interrelationship of Murexine, Dihydromurexine and Human Cholinesterases.

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Abstract
Murexine (Mur), the choline ester of urocanic acid, was recently tested clinically as a muscle relaxant. Both Mur and its reduced derivative dihydromurexine (DhMur), are hydrolyzed by concentrated human plasma cholinesterase (Cholase). The hydrolysis of Mur by Cholase was assayed both in a Beckman D.U. UV spectrophotometer at a wave length of 317 m[mu] and with Warburg''s manometric method. The hydrolysis of DhMur could only be determined with the manometric technique. The quantities of Mur and DhMur hydrolyzed by 1 ml of Cholase in 30 minutes were 13 x 10-3 [image] and 2.3 x 10-2 [image], respectively. Prostigmine inhibited the hydrolysis of both compounds. The Km of Mur was 1.1 x 10-5 [image], and that of DhMur 1.3 x 10-4 [image]. Human red cell "true" cholinesterase did not hydrolyze either Mur or DhMur. Mur inhibited the hydrolysis of acetylcholine (I50=8.2 x 10-4 [image]) and butyryl-choline (I50=4.9 x 10-3 [image]) by Cholase and the hydrolysis of acetylcholine by red cell cholinesterase (I50=3.6 x 10-3 [image]). DhMur inhibited only red cell cholinesterase (I50= 24 x 10-3 [image]).