Sulfate reduction in higher plants: molecular evidence for a novel 5'-adenylylsulfate reductase

Proc Natl Acad Sci U S A. 1996 Nov 12;93(23):13383-8. doi: 10.1073/pnas.93.23.13383.


Sulfate-assimilating organisms reduce inorganic sulfate for Cys biosynthesis. There are two leading hypotheses for the mechanism of sulfate reduction in higher plants. In one, adenosine 5'-phosphosulfate (APS) (5'-adenylysulfate) sulfotransferase carries out reductive transfer of sulfate from APS to reduced glutathione. Alternatively, the mechanism may be similar to that in bacteria in which the enzyme, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) reductase, catalyzes thioredoxin (Trx)-dependent reduction of PAPS. Three classes of cDNA were cloned from Arabidopsis thaliana termed APR1, -2, and -3, that functionally complement a cysH, PAPS reductase mutant strain of Escherichia coli. The coding sequence of the APR clones is homologous with PAPS reductases from microorganisms. In addition, a carboxyl-terminal domain is homologous with members of the Trx superfamily. Further genetic analysis showed that the APR clones can functionally complement a mutant strain of E. coli lacking Trx, and an APS kinase, cysC. mutant. These results suggest that the APR enzyme may be a Trx-independent APS reductase. Cell extracts of E. coli expressing APR showed Trx-independent sulfonucleotide reductase activity with a preference for APS over PAPS as a substrate. APR-mediated APS reduction is dependent on dithiothreitol, has a pH optimum of 8.5, is stimulated by high ionic strength, and is sensitive to inactivation by 5'-adenosinemonophosphate (5'-AMP). 2'-AMP, or 3'-phosphoadenosine-5'-phosphate (PAP), a competitive inhibitor of PAPS reductase, do not affect activity. The APR enzymes may be localized in different cellular compartments as evidenced by the presence of an amino-terminal transit peptide for plastid localization in APR1 and APR3 but not APR2. Southern blot analysis confirmed that the APR clones are members of a small gene family, possibly consisting of three members.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / metabolism*
  • Arabidopsis Proteins / physiology
  • Cloning, Molecular
  • Escherichia coli
  • Genetic Complementation Test
  • Kinetics
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Oxidoreductases
  • Oxidoreductases Acting on Sulfur Group Donors / chemistry
  • Oxidoreductases Acting on Sulfur Group Donors / metabolism*
  • Oxidoreductases Acting on Sulfur Group Donors / physiology
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Substrate Specificity
  • Sulfates / metabolism


  • Arabidopsis Proteins
  • Recombinant Proteins
  • Sulfates
  • Oxidoreductases
  • Oxidoreductases Acting on Sulfur Group Donors
  • 3'-phosphoadenylyl-5'-phosphosulfate reductase
  • APR2 protein, Arabidopsis
  • adenylylsulfate reductase

Associated data

  • GENBANK/AF016282
  • GENBANK/AF016283
  • GENBANK/AF016284
  • GENBANK/U43412
  • GENBANK/U56921
  • GENBANK/U56922