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The initial breakdown of adenosine and its phosphorylated derivatives is brought about by deamination or by dephosphorylation. Deaminases for these compounds are widely distributed in the tissues although in some organs (e.g. liver) they act only after dephosphorylation (Conway & Cooke, 1939). The influence of Mg++ on such deaminases has not been studied in great detail. Ostern & Mann (1933) claimed that Mg++ inhibits the deamination of adenosine triphosphate and of muscle adenylic acid by frog muscle extract whilst, usingmanmalian tissue extracts, Conway & Cooke (1939), working with adenosine and muscle adenylic acid, and Brady (1942), working with adenosine, found Mg++ to be without effect on the deamination of these compounds. The effect of Ca++ on these deaniinases has not, to our knowledge, been investigated. The effect of Mg++ and Ca++ on the dephosphorylation of adenosine triphosphate has been studied more closely. The liberation of the terminal phosphate group by myosin is activated by Ca++ (Needham, 1942; Bailey, 1942) and is inhibited by Mg++ (Lyubimova & Pevsner, 1941). The removal of the second phosphate group by myokinase is activated by Mg++ (Kalckar, 1943); the effect of Ca++ has not been tested. Our interest in this subject arose from a study of adenosine triphosphate as a metabolic factor possibly responsible for some of the general reactions to tissue trauma (Green, 1943; Bielschowsky & Green, 1943), a recent development of which was the finding that Mg++potentiates the shock-inducing action of adenosine triphosphate (Green & Stoner, 1944). The present work had the object of explaining the in vivo findings by a study of the effects ofMg++ and its pharmacological antagonist Ca++ on the breakdown of adenosine triphosphate and related compounds in vitro. No attempt was made to separate the enzyme systems concerned since it was desired to approximate the conditions as closely as possible to those withini the body.

The action of magnesium and calcium on the enzymic breakdown of certain adenine compounds