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

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Abstract
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 non‐physiological side reaction of APS‐kinase.