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Biochemistry (Moscow). Papers in Press. Published on March 8, 2021 as Manuscript BM20-320.

Catalytic Properties of Flavocytochrome c Sulfide Dehydrogenase from Haloalkaliphilic Bacterium Thioalkalivibrio paradoxus

Tamara V. Tikhonova1,a*, Anastasiya V. Lilina1, Evgenii M. Osipov1, Nikolay S. Shipkov1, Nataliya I. Dergousova1, Olga G. Kulikova1, and Vladimir O. Popov1

1Bach Institute of Biochemistry, Research Centre of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia

*To whom correspondence should be addressed.

Received September 25, 2020; Revised November 23, 2020; Accepted November 23, 2020
Flavocytochrome c sulfide dehydrogenase (FCC) is one of the central enzymes of the respiratory chain in sulfur-oxidizing bacteria. FCC catalyzes oxidation of sulfide and polysulfide ions to elemental sulfur accompanied by electron transfer to cytochrome c. The catalytically active form of the enzyme is a non-covalently linked heterodimer composed of flavin- and heme-binding subunits. The Thioalkalivibrio paradoxus ARh1 genome contains five copies of genes encoding homologous FCCs with an amino acid sequence identity from 36 to 54%. When growing on thiocyanate or thiosulfate as the main energy source, the bacterium synthesizes products of different copies of FCC genes. In this work, we isolated and characterized FCC synthesized during the growth of Tv. paradoxus on thiocyanate. FCC was shown to oxidize exclusively sulfide but not other reduced sulfur compounds, such as thiosulfate, sulfite, tetrathionate, and sulfur, and it also does not catalyze the reverse reaction of sulfur reduction to sulfide. Kinetic parameters of the sulfide oxidation reaction are characterized.
KEY WORDS: sulfur-oxidizing bacteria, flavocytochrome c sulfide dehydrogenase, thiocyanate dehydrogenase, enzyme kinetics

DOI: 10.1134/S0006297921030111