Cytidylate cyclase activity: Identification of cytidine 3′,5′‐cyclic monophosphate and four novel cytidine cyclic phosphates as biosynthetic products from cytidine triphosphate

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Abstract
Identification of cytidine 3′,5′-cyclic monophosphate (cyclic CMP) as one of the products resulting from the incubation of dialysed cell-free preparations from rat brain, liver and kidney with cytidine 5′-triphosphate (CTP) is described. The non-acidic precipitable products after incubation of the tissue preparations with unlabelled, with 14C-single labelled, and with 14C- and 32P-dual labelled CTP were examined by thin-layer chromatography and high-pressure liquid chromatography, isotopic ratio determination, UV absorbance spectrophotometry, selective hydrolysis with nucleotidase, phosphodiesterase and acid, and by fast atom bombardment mass spectrometry with mass-analysed ion kinetic energy spectrum scanning. In addition to cyclic CMP and unchanged CTP, the products of the reaction were found to include cytidine monophosphate (CMP) and cytidine diphosphate (CDP) together with four novel cytidine compounds identified as cytidine 3′,5′-cyclic pyrophosphate, cytidine 2′-monosphosphate 3′,5′-cyclic monophosphate, cytidine 2′-O-aspartyl-3′,5′-cyclic monophosphate and cytidine 2′-O-glutamyl-3′,5′-cyclic monosphate. The evidence presented constitutes conclusive proof of the natural occurrence of cytidylate cyclase activity; the four novel cytidine cyclic phosphates described provide a feasible explanation of the discrepancies in previous reports which have led to the controversy which exists concerning the existence of cytidylate cyclase activity.