title: Assimilatory sulfate reduction by choloroplasts: the regulatory influence of adenosine-mono-and adenosine-diphosphate.
abstract: The first three enzymatic steps of assimilatory sulfate reduction in chloroplasts of higher plants have been investigated with emphasis on the influence of adenosine-mono-and-diphosphate upon the formation of APS, PAPS and bound sulfite. The data show that the activation process is governed by the energy charge of the chloroplast. The regulatory step is localized at the ATP-sulfurylase reaction. It was found that this enzyme is inhibited by low concentrations of AMP and ADP, with apparent KiAMP=1.8 mM and KiADP=0.5 mM for the chloroplast preparations. The isolated purified ATP-sulfurylase is inhibited by the nucleotides accordingly, with KiAMP=0.2 mM and KiADP=0.4 mM. The results are interpreted as a regulatory mechanism for the complete process of assimilatory sulfate reduction in the chloroplast.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000249:Adenosine Monophosphate / Q000494:pharmacology*; D000255:Adenosine Triphosphate; D002736:Chloroplasts / Q000378:metabolism*; D007700:Kinetics; D009713:Nucleotidyltransferases / Q000378:metabolism; D010944:Plants; D011755:Pyrophosphatases / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism*
chemical_list: D013431:Sulfates; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009713:Nucleotidyltransferases; D011755:Pyrophosphatases