title: Derepression of ATP sulfurylase by the sulfate analogs molybdate and selenate in cultured tobacco cells.
abstract: Molybdate and selenate are structural analogs of sulfate that inhibit synthesis of adenosine 5'-phosphosulfate by ATP sulfurylase (sulfate adenylyltransferase, ATP:sulfate adenylyltransferase, EC 2.7.7.4) in crude extracts of tobacco XD cells. Both of these anions derepress ATP sulfurylase in cells growing on sulfate, but not in cells growing on L-cysteine. However, the two anions appear to derepress by different mechanisms. Molybdate caused derepression only at concentrations that were in excess over sulfate and were sufficient to inhibit growth and protein accumulation, indicating that the derepression resulted from sulfur starvation. Selenate caused derepression at one-tenth the concentration of sulfate, a concentration of selenate that was subtoxic, while toxic levels of selenate produced far less derepression. The susceptibility of the tobacco cells to selenate toxicity was high under conditions of sulfur nutrition that derepress ATP sulfurylase, and low under conditions that repress ATP sulfurylase, in agreement with the idea that selenate acts via a functional sulfate assimilation pathway. Since it is known that selenate is incorporated into analogs of sulfur compounds, it is proposed that the tobacco cells synthesize the seleno-analog of the end product of the sulfate pathway responsible for repression, and the seleno-analog antagonizes the normal end product in the repression mechanism, the net result being derepression of ATP sulfurylase by selenate.
mesh_terms: D000255:Adenosine Triphosphate; D002478:Cells, Cultured; D004794:Enzyme Repression / Q000187:drug effects; D007700:Kinetics; D008982:Molybdenum / Q000494:pharmacology*; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010944:Plants / Q000201:enzymology*; D010947:Plants, Toxic; D012643:Selenium / Q000494:pharmacology*; D013431:Sulfates / Q000494:pharmacology*; D014026:Nicotiana / Q000201:enzymology*
chemical_list: D013431:Sulfates; D008982:Molybdenum; D000255:Adenosine Triphosphate; D009713:Nucleotidyltransferases; D012643:Selenium
references.citation: Anal Biochem. 1976 Oct;75(2):410-28
references.pmid: 790997
references.citation: Biochim Biophys Acta. 1971 Feb 10;227(2):373-89
references.pmid: 4323859
references.citation: Biochem J. 1974 Apr;139(1):37-42
references.pmid: 4377098
references.citation: Biochem J. 1972 Mar;127(1):237-47
references.pmid: 5073745
references.citation: Biochim Biophys Acta. 1970 Jan 6;196(1):95-106
references.pmid: 5412251
references.citation: Biochim Biophys Acta. 1971 Feb 23;230(2):362-72
references.pmid: 5573364
references.citation: Nature. 1968 Jul 20;219(5151):268-70
references.pmid: 5671427
references.citation: Biochem J. 1953 Aug;55(1):170-1
references.pmid: 13093635
references.citation: J Biol Chem. 1958 Oct;233(4):975-81
references.pmid: 13587526
references.citation: Plant Physiol. 1969 Sep;44(9):1253-9
references.pmid: 16657199