Schematic representation of the cellular metabolism of sulfate Schematic representation of the cellular metabolism of sulfate. The numbers on the right refer to the following steps: (1) Sulfate/chloride exchange by DTDST. The stoichiometry has not been determined directly, but since the transporter is not ATP-dependent and electrogenic, it is assumed to be two chloride ions for one sulfate ion. (2) Sulfite oxidase, catalyzing final oxidation of thiol-derived sulfite to sulfate (see Chaps. 88 & 128). (3, 4) Metabolic activation of inorganic sulfate by the bifunctional enzyme ATP sulfurylase-APS kinase (ATPSK). (5) Translocation of PAPS into the endoplasmic reticulum by a putative PAPS/PAP antiporter. Source: Defects in Sulfate Metabolism and Skeletal Dysplasias, The Online Metabolic and Molecular Bases of Inherited Disease Citation: Valle D, Beaudet AL, Vogelstein B, Kinzler KW, Antonarakis SE, Ballabio A, Gibson K, Mitchell G. The Online Metabolic and Molecular Bases of Inherited Disease; 2014 Available at: http://ommbid.mhmedical.com/DownloadImage.aspx?image=/data/books/971/ch202fg1.png&sec=62656623&BookID=971&ChapterSecID=62656614&imagename= Accessed: October 19, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved