Kinetic Observations on Cholinesterase Activities of Rat Brain and Sympathetic Ganglion towards Biochemical and Histochemical Substrates

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Abstract
Cholinesterase activities of homogenates of rat brain and superior cervical ganglion were measured by automatic titration at pH 8. Acetylcholine, acetylthiocholine, acetyl‐β‐methylcholine, propionylcholine, propionylthiocholine, α‐naphthyl acetate, butyrylcholine, butyrylthiocholine and benzoylcholine were used as substrates. As selective inhibitors of specific and nonspecific cholinesterases, 1: 5‐bis‐(4‐allyl dirnethylammoniumphenyl) pentan‐3‐one diiodide (284 C 51) and tetra‐isopropylpyrophosphoramide (iso‐OMPA) were used, respectively. Acetyl‐β‐methylcholine and α‐naphthyl acetate were mainly split by specific cholinesterase, butyrylcholine was predominantly hydrolyzed by non‐specific cholinesterase, while acetylcholine, acetylthiocholine, propionylcholine and propionylthiocholine were readily split by both enzymes. Michaelis—Menten constants, determined by the Lineweaver‐Burk procedure, were equal for acetylcholine and propionylcholine, on the one hand, and for acetylthiocholine and propionylthiocholine, on the other. The specific (284 C 51‐sensitive) components of the cholinesterase activities of these 4 substrates showed strong inhibition by excess substrate, while the non‐specific activity towards the same substrates increased with increasing substrate concentration. When 2 of these substrates were in turn used together as substrates, no additive increase of activity was observed. It is concluded that propionylcholine and propionylthiocholine serve, like acetylcholine and acetylthiocholine, as substrates of both specific and non‐specific cholinesterases in rat brain and sympathetic ganglion.
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