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Crude rat liver extract showed AMP–AMP phosphotransferase activity which, on purification, was ascribed to a novel interaction between adeny-late kinase, also known as myokinase (EC 2.7.4.3), and adenosine kinase (EC 2.7.1.20). The activity was duplicated using the same enzymes purified from recombinant sources. | ỊFEBS Journal Evidence of a new phosphoryl transfer system in nucleotide metabolism Daniela Vannoni1 Roberto Leoncini1 Stefania Giglioni1 Neri Niccolai2 Ottavia Spiga2 Emilia Aceto1 and Enrico Marinello1 1 Department of InternalMedicine Endocrine-Metabolic Sciences and Biochemistry University of Siena Italy 2 Department of Molecular Biology University of Siena Italy Keywords adenosine deaminase adenosine kinase adenylate kinase ADP ATP Correspondence R. Leoncini Department of Internal Medicine Endocrine-Metabolic Sciences and Biochemistry Via A. Moro 2 53100 Siena Italy Fax 39 0577 234285 Tel 39 0577 234287 E-mail leoncini@unisi.it These authors contributed equally to this work Received 16 July 2008 revised 24 September 2008 accepted 5 November 2008 Crude rat liver extract showed AMP-AMP phosphotransferase activity which on purification was ascribed to a novel interaction between adenylate kinase also known as myokinase EC 2.7.4.3 and adenosine kinase EC 2.7.1.20 . The activity was duplicated using the same enzymes purified from recombinant sources. The reaction requires physical contact between myokinase and adenosine kinase and the net reaction is aided by the presence of adenosine deaminase EC 3.5.4.4 which fills the gap in the energy balance of the phosphoryl transfer and shifts the equilibrium towards ADP and inosine synthesis. The proposed mechanism involves the association of adenosine kinase and myokinase through non-covalent transient interactions that induce slight conformational changes in the active site of myokinase bringing two already bound molecules of AMP together for phosphoryl transfer to form ADP. The proposed mechanism suggests a physiological role for the enzymes and for the AMP-AMP phosphotransferase reaction under conditions of extreme energy drain such as hypoxia or temporary anoxia as in cancer tissues when the enzymes cannot display their conventional activity because of substrate deficiency. doi 10.1111 j.1742-4658.2008.06779.x Purine .
