The sulfane sulfur of persulfides is the actual substrate of the sulfur-oxidizing enzymes from Acidithiobacillus and Acidiphilium spp.
To identify the actual substrate of the glutathione-dependent sulfur dioxygenase (EC 1.13.11.18) elemental sulfur oxidation of the meso-acidophilic Acidithiobacillus thiooxidans strains DSM 504 and K6, Acidithiobacillus ferrooxidans strain R1 and Acidiphilium acidophilum DSM 700 was analysed. Extraordinarily high specific sulfur dioxygenase activities up to 460 nmol x min(-1) (mg protein)(-1) were found in crude extracts. All cell-free systems oxidized elemental sulfur only via glutathione persulfide (GSSH), a non-enzymic reaction product from glutathione (GSH) and elemental sulfur. Thus, GSH plays a catalytic role in elemental sulfur activation, but is not consumed during enzymic sulfane sulfur oxidation. Sulfite is the first product of sulfur dioxygenase activity; it further reacted non-enzymically to sulfate, thiosulfate or glutathione S-sulfonate (GSSO(-3)). Free sulfide was not oxidized by the sulfur dioxygenase. Persulfide as sulfur donor could not be replaced by other sulfane-sulfur-containing compounds (thiosulfate, polythionates, bisorganyl-polysulfanes or monoarylthiosulfonates). The oxidation of H(2)S by the dioxygenase required GSSG, i.e. the disulfide of GSH, which reacted non-enzymically with sulfide to give GSSH prior to enzymic oxidation. On the basis of these results and previous findings a biochemical model for elemental sulfur and sulfide oxidation in Acidithiobacillus and Acidiphilium spp. is proposed.
Rohwerder
Thore
T
Department of Microbiology, Institute for General Botany, University of Hamburg, Ohnhorststr. 18, D-22609 Hamburg, Germany.
Sand
Wolfgang
W
Department of Microbiology, Institute for General Botany, University of Hamburg, Ohnhorststr. 18, D-22609 Hamburg, Germany.
D016947:Acetobacteraceae / Q000201:enzymology*; D049308:Dioxygenases; D020563:Gammaproteobacteria / Q000201:enzymology*; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism; D019803:Glutathione Disulfide / Q000737:chemistry / Q000378:metabolism; D006862:Hydrogen Sulfide / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000378:metabolism*; D013379:Substrate Specificity; D013440:Sulfides / Q000737:chemistry / Q000378:metabolism*; D013455:Sulfur / Q000737:chemistry
D013440:Sulfides; C051552:persulfides; D013455:Sulfur; D010105:Oxygenases; D049308:Dioxygenases; C477654:sulfur dioxygenase; D005978:Glutathione; D019803:Glutathione Disulfide; D006862:Hydrogen Sulfide