APS-sulfotransferase activity is identical to higher plant APS-kinase (EC 2.7.1.25).

A cDNA from Arabidopsis thaliana L. Heynh encoding the APS-kinase (EC 2.7.1.25) was modified by deletion of a plastidic transit peptide to enable its expression in Escherichia coli. The resultant protein (MW 25,761) is enzymatically active as APS-kinase and restores prototrophic growth in an APS-kinase mutant. All transformants harbouring the modified plant DNA also acquired APS-sulfotransferase activity. In the absence of ATP but provided with DTT, a tetrameric form of recombinant APS-kinase exhibits APS-sulfotransferase activity. Monospecific polyclonal antibodies raised against the APS-kinase as immunogen also reacted against APS-sulfotransferase. We propose that APS-sulfotransferase activity is a nonphysiological side reaction of APS-kinase.