. Cell chemistry; a collection of papers dedicated to Otto Warburg on the occasion of his 70th birthday. Warburg, Otto Heinrich, 1883-; Biochemistry. 320 R. BERMAN, I. B. WILSON, D. NACHMANSOHN VOL. 12 (1953) uM ester formed centration is about the Michaelis-Menten constant for acetyl CoA. The immsasurably low reactivity of butyryl CoA is not, however, due to poor binding. This is illustrated b}- the fact that butyryl CoA in equal concentration with acetyl CoA inhibits the rate of acylation of choline by approximately 80%. Fig. 3. Effect of the acyl group of CoA derivatives on the acylation of
. Cell chemistry; a collection of papers dedicated to Otto Warburg on the occasion of his 70th birthday. Warburg, Otto Heinrich, 1883-; Biochemistry. 320 R. BERMAN, I. B. WILSON, D. NACHMANSOHN VOL. 12 (1953) uM ester formed centration is about the Michaelis-Menten constant for acetyl CoA. The immsasurably low reactivity of butyryl CoA is not, however, due to poor binding. This is illustrated b}- the fact that butyryl CoA in equal concentration with acetyl CoA inhibits the rate of acylation of choline by approximately 80%. Fig. 3. Effect of the acyl group of CoA derivatives on the acylation of choHne by choHne acetylase. The reaction mixture contained 140 ^g enzyme and the following com- ponents in fiM per ml: choline 20, phosphate buffer, pH 7, 90, acyl CoA either 4 or 8. Total volume i ml, t = 31° h 4 /iiM acetyl CoA + 8 /nM acetyl CoA O O 4 juM propionyl CoA # # 8 fiM propionyl CoA D *-mm D 4 and 8 /nM butyryl CoA resp. £ /[juM acetyl Co A + 4 ^Af butyryl Co A. DISCUSSION The specificity patters of choline acetylase assumes enhanced biological interest when the acetylase is recognized as part of a physiological system, the acetylcholine system, which is directly involved in conduction. It is important to compare this enzyme with the other members ot the system to ascertain if any underlying unity exists. It is consequently pertinent to describe, albeit very briefly, the mechanism of the system as it is presently envisaged^-^. Acetylcholine is in a bound state during rest; it is released in activity to react with a receptor and is finally destroyed by acetylcholine- esterase, a step essential for the rapid short range recovery of function. Complete re- covery in a long range sense is accomplished by the resynthesis of acetylcholine mediated by choline acetylase. The receptor, presumably a protein or a conjugated protein, is assumed to determine the membrane characteristics associated with such phenomena as ion permeability and electrical potential. The combi
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