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Some Properties of Adenyl Cyclase from Ehrlich Tumor Cells¹

Institute of Medical Chemistry, University of Uppsala, Box 551, S-751 22 Uppsala 1, Sweden

Adenyl cyclase from Ehrlich tumor cells has a temperature optimum of 37° and is maximally stimulated by 10 mM NaF. The pH optimum of the enzyme lies between 7.8 and 8.2. At pH values less than 7.2, the activity is very low. The formation of cyclic adenosine 3',5'-monophosphate in the presence of 10 mM NaF was further stimulated by 10 mM caffeine. Mg⁺⁺ ions were essential for tumor cyclase activity, which was inhibited by 10 mM Ca⁺⁺ and 10 mM EDTA. The tumor cyclase exhibited normal Michaelis-Menten kinetics. The K_m for adenosine triphosphate at 5 mM Mg⁺⁺ was 0.28 mM; 0.1 mM cyclic adenosine 3',5'-monophosphate and 1 mM adenosine monophosphate were both inhibitory to the enzyme, which had an absolute substrate specificity for adenosine triphosphate. The inhibitory effect of the nucleotides was not additive. Therefore it was concluded that adenosine monophosphate as well as cyclic adenosine 3',5'-monophosphate may serve as negative effectors acting on the same site.

¹ This investigation was supported by grants from the Swedish Medical Research Council (Project B73-13X-228-09B8) and the Swedish Cancer Society (Project 290-B72-04X).

Received 3/ 5/73. Accepted 6/18/73.