| Abstract: | The spontaneous formation of arsenic mononucleotides has been detected in mixtures of arsenate and inosine or adenosine or its deoxy analogues. These compounds have been separated by high-performance liquid chromatography and identified by their behavior in the presence of myokinase and adenylate deaminase. The nucleoside 5'-arsenates are formed preferentially to the 2'- and 3'-arsenate analogues. All arsenic nucleotides detected showed similar kinetic and equilibrium constants of formation: about 8 X 10(-4) M-1 S-1 and 2 X 10(-3) M-1, respectively. These values are several orders of magnitude greater than those of their phosphoric analogues. The adenosine 5'-arsenate was able to substitute for 5'AMP in the reaction of myokinase and adenylate deaminase. The substitutions of the 2'- or 3'-hydrogen for hydroxyl groups in the ribose moiety of this compound slightly affected its suitability as substrate for myokinase but had drastic effect in the case of adenylate deaminase. The half-life of the arsenic nucleotides, at pH 7.0 and 25 degrees C, ranged from 30 to 45 min. The lability of these compounds is increased during catalysis with myokinase. Results on the reaction mechanism of myokinase with adenosine 5'-arsenate indicate that the mixed-anhydride analogue to ADP, adenosine 5'-(arsenate phosphate), is not detected either because it is not formed in the reaction with this enzyme or because it is rapidly hydrolyzed. |
