Fluoride inhibition of SCN- and Cl-peroxidase activities in whole saliva and of recombinant myeloperoxidase. Influence of pH and hydrogen peroxide concentration.
Fluoride (F-) inhibition of peroxidase activity in whole saliva and of recombinant human myeloperoxidase was investigated using thiocyanate (SCN-) and chloride (Cl-) as substrates. At pH 5.5, SCN(-)-linked activity in whole saliva reduced to < 40% of its initial value at F- concentration of 20 mM, while Cl- linked activity was maintained at 90% of its initial value for the same F-concentration. Based on this Cl(-)-linked activity, the contribution of natural MP to the SCN(-)-linked activity in whole saliva can be calculated. This shows a total inhibition of SCN- dependent activity of salivary peroxidase (SP) for F-concentrations > 10 mM. At a 20 mM F-concentration, recombinant MP activity reduced to 66% of its initial value with SCN-, against 88% for Cl- as substrate. This inhibition of the SCN- linked SP activity is enhanced at acid pH for a F-concentration of 20 mM: 26% residual activity at pH 5 for whole saliva + SCN-against 93% for whole saliva + Cl-; 61% for recombinant MP + SCN- and 88% for MP + Cl-. Calculated activities for SP alone showed a total inhibition at pH 5, while the inhibition was absent at pH 6.5. F-inhibition in whole saliva could also be suppressed by the addition of hydrogen peroxide.
van den Abbeele
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Laboratoire de Stomatologie, Université Libre de Bruxelles, Faculté de Médecine, Belgium.
Pourtois
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Courtois
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D000328:Adult; D002712:Chlorides / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005459:Fluorides / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000037:antagonists & inhibitors*; D010544:Peroxidases / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins; D012463:Saliva / Q000737:chemistry / Q000201:enzymology*; D013861:Thiocyanates / Q000378:metabolism*
D002712:Chlorides; D011994:Recombinant Proteins; D013861:Thiocyanates; D006861:Hydrogen Peroxide; D010544:Peroxidases; D009195:Peroxidase; C031760:thiocyanate; D005459:Fluorides