Selenium-dependent and selenium-independent formate dehydrogenases of Methanococcus vannielii. Separation of the two forms and characterization of the purified selenium-independent form.
1981; Elsevier BV; Volume: 256; Issue: 2 Linguagem: Inglês
10.1016/s0021-9258(19)70024-6
ISSN1083-351X
AutoresJ. B. Jones, Thressa C. Stadtman,
Tópico(s)Enzyme Structure and Function
ResumoAnaerobic oxidation of formate byMethanococcus vannielii is catalyzed by two readily separable formate dehydrogenases.One of these is a 105,000-dalton protein that contains molybdenum, iron, and acid-labile sulfide, but not selenium.The other is a high molecular weight complex composed of selenoprotein and molybdo-iron sulfur protein subunits.Selenium occurs in this selenoenzyme in the chemical form of selenocysteine residues.M. uannielii cells from selenium-deficient media contain the 105,000-dalton formate dehydrogenase.Marked stimulation of growth by selenite supplementation is correlated with the simultaneous appearance in the cells of the high molecular weight selenoprotein-enzyme complex.The latter is the predominant form in cells from media additionally supplemented with tungstate.Under these conditions partial replacement of molybdenum with tungsten appears to occur.Both formate dehydrogenases are maximally active at pH 8.5 to 9.2 and at 60°C and are extremely oxygen-sensitive.They utilize as electron acceptors 8- hydroxy-5-deazaflavin, FMN, FAD, and viologen and tetrazolium dyes.Methanococcus vannielii ferments formate to carbon dioxide and methane according to Reaction 1. HCOOHIn early studies with this organism rapid growth was attained in a formate/mineral salts medium prepared in tap water that was not supplemented with selenium (1,2).Later, however, when it became necessary to use distilled water because of the presence of toxic detergents in the domestic water supply, slow and erratic growth was observed.Rapid growth and improved cell yields again were attained when the distilled water media were supplemented with 1 pM sodium selenite and the further addition of 100 p~ sodium tungstate enhanced the growth rate and cell yield even more (2, 3).In Escherichia coli, elaboration of formate dehydrogenase activity is completely dependent on the availability of the trace elements, molybdenum and selenium (4, 5 ) , which are
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