Brain choline acetylase

Hlley and Burgen (58) measured also the choline acetylase and acetylcholinesterase activities of selected areas of the brain. In an attempt to determine whether the concentration of muscarinic receptors in a location was related to either of these enzyme activities. The amount of Che labeled prppylbenzllylchollne mustard bound was not well correlated with either the choline acetylase or the acetylcholinesterase activity there was a modest correlation between binding of the model agonist by synapcosomes and membranes prepared from nine areas of brain and the choline acetylase activities of the same areas, but It was far from precise. 

Yamamura et al. found that uptake of the label by various areas of brain had a tendency to be correlated with choline uptake and with choline acetylase activity. 

Esters of carboxylic acids are prominent among the chemical structures of biological systems. The biosyntheses of only a few of the naturally occurring esters have been studied enzymatically. Among the known reactions are the syntheses of acetylchohne and of phosphatidic acids. Acetylcholine is formed by choline acetylase, which has been purified from nervous tissue. Nachmansohn and associates have prepared choline acetylase from rat brain, the electric organ of the electric eel, squid ganglia, and other tissues. It has been detected in muscle also, but not in liver or kidney. The reaction is very similar to the acetylation of amines. 

For the analysis of enzyme mechanisms cell-free extracts are preferable. In agreement with the conclusion above an enzyme, choline acetylase, has been extracted from brain which in the presence of ATP, in a cell-free solution, and imder anaerobic conditions synthesizes ACh (Nachmansohn and Machado, 109). Only nervous tissue seems to contain the enzyme. Kidney, liver, and muscle do not contain measurable amounts. Extracts prepared from one gram of rat or of guinea pig brain form 120-160 Mg of ACh in GO min. (Nachmansohn and John, 111). Extracts from cat and... 

On dialysis, the activity of choline acetylase decreases rapidly. After two hours of dialysis the enzyme loses about 80 to 85 per cent of its activity. Clinical observations suggest that glutamic acid has a favorable effect on epileptic patients suffering from petit mal attacks, whereas patients with grand mat do not appear to be affected (Price, Waelsch, Putnam, 120). On the hypothesis that the slow waves which appear in the electroencephalogram during attacks of petit mal may in some way be connected with a lower rate of formation of ACh, the effect of glutamic acid has been tested on the synthesis of ACh in dialyzed extracts of rat brain. 

Choline acetylase may also be extracted from powder of acetone-dried brain. In these preparations choline esterase is destroyed to a large extent. Sometimes the destruction of choline esterase is neatly complete. In this way the two enzymes may be separated (Nachmansohn and John, 111)... 

An enzyme, choline acetylase, has been extracted from brain which in presence of adenosine triphosphate and under anaerobic conditions forms ACh. Some properties of the newly discovered enzyme are described. 

---