title: 1,2-Dichlorobenzene affects the formation of the phosphoenzyme stage during the catalytic cycle of the Ca(2+)-ATPase from sarcoplasmic reticulum.
abstract: BACKGROUND
  1,2-Dichlorobenzene (1,2-DCB) is a benzene-derived molecule with two Cl atoms that is commonly utilized in the synthesis of pesticides. 1,2-DCB can be absorbed by living creatures and its effects on naturally-occurring enzymatic systems, including the effects on Ca(2+)-ATPases, have been poorly studied. Therefore, we aimed to study the effect of 1,2-DCB on the Ca(2+)-ATPase from sarcoplasmic reticulum (SERCA), a critical regulator of intracellular Ca(2+) concentration.
  
  
  RESULTS
  Concentrations of 0.05-0.2 mM of 1,2-DCB were able to stimulate the hydrolytic activity of SERCA in a medium-containing Ca(2+)-ionophore. At higher concentrations (0.25-0.75 mM), 1,2-DCB inhibited the ATP hydrolysis to ~80 %. Moreover, ATP hydrolysis and Ca(2+) uptake in a medium supported by K-oxalate showed that starting at 0.05 mM,1,2-DCB was able to uncouple the ratio of hydrolysis/Ca(2+) transported. The effect of this compound on the integrity of the SR membrane loaded with Ca(2+) remained unaffected. Finally, the analysis of phosphorylation of SERCA by [γ-(32)P]ATP, starting under different conditions at 0° or 25 °C showed a reduction in the phosphoenzyme levels by 1,2-DCB, mostly at 0 °C.
  
  
  CONCLUSIONS
  The temperature-dependent decreased levels of phosphoenzyme by 1,2-DCB could be due to the acceleration of the dephosphorylation mechanism - E2P · Ca2 state to E2 and Pi, which explains the uncoupling of the ATP hydrolysis from the Ca(2+) transport.
authors.affiliation: Present address: Department of Biomedical Sciences, Center of Emphasis for Neurosciences, Texas Tech University Health Science Center, El Paso, TX, 79905, USA.
authors.forename: Javier
authors.initials: J
authors.lastname: Vargas-Medrano
authors.affiliation: Present address: Department of Biological Sciences, University of Texas at El Paso, El Paso, TX, 79968, USA.
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Sierra-Fonseca
authors.affiliation: Departamento de Ciencias Químico Biológicas, Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, Plutarco Elías Calles #1210 Fovissste Chamizal, Ciudad Juárez, Chihuahua, C.P. 32310, Mexico. fplenge@uacj.mx.
authors.forename: Luis F
authors.initials: LF
authors.lastname: Plenge-Tellechea
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D055162:Biocatalysis; D002118:Calcium / Q000378:metabolism; D002722:Chlorobenzenes / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D018482:Muscle, Skeletal / Q000378:metabolism; D019815:Oxalic Acid / Q000737:chemistry / Q000378:metabolism; D010575:Pesticides / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013696:Temperature
chemical_list: D002722:Chlorobenzenes; D010575:Pesticides; C004726:2-dichlorobenzene; D000255:Adenosine Triphosphate; D019815:Oxalic Acid; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium
keywords: Ca2+-ATPase; Dichlorobenzene; Phosphoenzyme; Sarcoplasmic reticulum