Roles of Ala-149 in the catalytic activity of diadenosine tetraphosphate phosphorylase from <i>Mycobacterium tuberculosis</i> H37Rv

<div><p>Diadenosine 5′,5′′′-<i>P</i><sup>1</sup>,<i>P</i><sup>4</sup>-tetraphosphate (Ap<sub>4</sub>A) phosphorylase from <i>Mycobacterium tuberculosis</i> H37Rv (MtAPA) belongs to the histidine triad motif (HIT) superfamily, but is the only member with an alanine residue at position 149 (Ala-149). Enzymatic analysis revealed that the Ala-149 deletion mutant displayed substrate specificity for diadenosine 5′,5′′′-<i>P</i><sup>1</sup>,<i>P</i><sup>5</sup>-pentaphosphate and was inactive on Ap<sub>4</sub>A and other substrates that are utilized by the wild-type enzyme.</p></div>