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FOLLOWING the discovery by Stedman et al. [1932] that the destruction of acetylcholine by blood serum was brought about by a specific enzyme, which they termed choline-esterase, Stedman et al. [1933] examined the blood sera from a number of species for the presence of this enzyme and compared the cholineesterase activities of these sera with their activities towards two other types of esters, namely, methyl butyrate and tributyrin. The results offered ample confirmation, if such were needed, of the specific nature of choline-esterase. It was further demonstrated that sera from different species differed widely with respect to their content of the enzyme in question, those from certain species being, in fact, so deficient in it that none was detectable by the method of estimation which was employed. It was, however, emphasised that the virtual absence of the enzyme from serum did not necessarily imply its absence from the corpuscles, the choline-esterase activities of which could not at the time be determined since the method of estimation used with serum was not applicable to whole blood or to corpuscles. In order to examine this point the present authors have therefore developed a method for the estimation of choline-esterase in corpuscles, defibrinated blood or tissue and have used it to determine the distribution of the enzyme between corpuscles and serum in the blood of a number of species. This work is described in the present communication. Since this investigation, which was reported to the Meeting of the Biochemical Society in Glasgow in June 1934, was completed papers have appeared on the same subject by Ammon [1934] and Ammon and Voss [1935] in which a method for the determination of cholineesterase is described which is identical in principle with that employed in the present work. Inasmuch, however, as Ammon employs a Warburg apparatus whereas we utilise the Barcroft differential apparatus our experimental procedure differs from that of the German workers. The material which we have examined is, moreover, by no means completely identical with that investigated by Ammon. Estimation of choline-esterase.

The relative choline-esterase activities of serum and corpuscles from the blood of certain species