Characterisation of Adenosine 5'phosphosulfate (APS) Kinase from onion (Allium cepa L.)

摘要

In higher plants, uptaken sulfate is transported to the chloroplast where the assimilation pathway occurs. Initially, sulfate is activated by ATP to form adenosine 5'-phosphosufate (APS) by the enzyme ATP sulfurylase (E.C.2.7.7.4). APS is then a substrate for two enzymes. The reductive pathway produces the amino acid cysteine and is initiated by APS reductase (E.C.I.8.99.2). In the secondary pathway, APS is phosphorylated by APS kinase (E.C.2.7.1..25) to form 3'-phosphoadenosine 5'-phosphosulfate (PAPS), a precursor to plant secondary metabolites, such as glucosinolates, which are important plant protectant molecules. In higher plants, APS kinase (APSK) has mainly been investigated in members of the glucosinilate-accumulating Brassicaceae. For example, four isoforms have been found in Arabidopsis, with APSK1 being the main isoform involved in the production of glucosinolates.