Purification and characterization of sulfide-quinone reductase, a novel enzyme driving anoxygenic photosynthesis in Oscillatoria limnetica.
An enzyme catalyzing sulfide quinone oxido-reduction (E.C.1.8.5.'.; SQR) has been purified in an active form, from thylakoids of the cyanobacterium Oscillatoria limnetica. It is composed of a single polypeptide of about 57 kDa. The catalytic activity of the purified enzyme is similar to the membrane-bound form in its kinetic parameters: apparent Km for sulfide equals 8 microM; Vmax of 100-150 mumol of plastoquinone-1 reduced/mg protein/h; quinone-substrate specificity; differential sensitivity to quinone analog inhibitors, the most potent of which being aurachin C (I50 = 7 nM), and specific inducibility by sulfide. Taken together, they suggest that the purified SQR is the enzyme catalyzing anoxygenic photosynthesis in cyanobacteria. The UV and visible absorption and fluorescence spectra of the purified SQR are typical of a flavoprotein. Both the absorption and fluorescence intensities are reduced by sulfide. The SQR activity is inhibited by KCN, a flavoprotein inhibitor. We have sequenced so far 29 amino acid residues of the SQR NH2 terminus and found that from the second residue, this sequence contains the highly conserved fingerprint of the NAD/FAD-binding domain of many NAD/FAD-binding enzymes (Wierenga, R. K., Terpstra, P., and Hol, W. G. S. (1986) J. Mol. Biol. 187, 101-107). This suggests that the SQR enzyme is a flavoprotein which contains binding sites for sulfide and quinone and that the electron transfer between the two is mediated by FAD.
Arieli
B
B
Division of Microbial and Molecular Ecology, Hebrew University of Jerusalem, Israel.
Shahak
Y
Y
Taglicht
D
D
Hauska
G
G
Padan
E
E
D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D000458:Cyanobacteria / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004790:Enzyme Induction; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D011808:Quinone Reductases / Q000096:biosynthesis / Q000302:isolation & purification* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013057:Spectrum Analysis; D013379:Substrate Specificity; D013440:Sulfides / Q000494:pharmacology
D013440:Sulfides; D011808:Quinone Reductases; C073412:sulfide quinone reductase; D010100:Oxygen