The ATP:Co(I)rrinoid Adenosyltransferase (CobA) Enzyme of \u3ci\u3eSalmonella enterica\u3c/i\u3e Requires the 2\u27-OH Group of ATP for Function and Yields Inorganic Triphosphate as Its Reaction Byproduct

The specificity of the ATP:corrinoid adenosyltransferase (CobA) enzyme of Salmonella enterica serovar Typhimurium LT2 for its nucleotide substrate was tested using ATP analogs and alternative nucleotide donors. The enzyme showed broad specificity for the nucleotide base and required the 2’-OH group of the ribosyl moiety of ATP for activity. 31P NMR spectroscopy was used to identify inorganic triphosphate (PPPi) as the byproduct of the reaction catalyzed by the CobA enzyme. Cleavage of triphosphate into pyrophosphate and orthophosphate did not occur, indicating that triphosphate cleavage was not required for release of the adenosylcorrinoid product. Triphosphate was a strong inhibitor of the reaction, with 85% of CobA activity lost when the ATP/PPPi ratio present in the reaction mixture was 1:2.5