The sulfate assimilation pathway of <i>Mtb</i>.

<p>Inorganic sulfate from the host is converted to APS by ATP sulfurylase. APS is either sequentially reduced by APS reductase and sulfite reductase for the biosynthesis of essential reduced sulfur metabolites (reductive branch), or phosphorylated by APS kinase to generate PAPS, a substrate for sulfotransferases (sulfation branch). PAP, a byproduct of sulfotransferase reactions, is degraded by the PAP(S) phosphatase CysQ, which also converts PAPS to APS.