Sulfite reductase types

Molitor, M., Dahl, C., Molitor, I. 5 others 1998. A dissimilatory siro-haem-sulfite-reductase-type protein from the hyperthermophile archaeon. Pyrobaculum islandicum. Microbiology, 144, 529-541. 

Sulfite reductase catalyzes the six-electron reduction of sulfite to sulfide, m essential enzymatic reaction in the dissimilatory sulfate reduction process. Several different types of dissimilatory sulfite reductases were already isolated from sulfate reducers, namely desul-foviridin (148-150), desulforubidin (151, 152), P-582 (153, 154), and desulfofuscidin (155). In addition to these four enzymes, an assimila-tory-type sulfite reductase was also isolated from D. vulgaris. Although all these enzymes have significantly different subunit composition and amino acid sequences, it is interesting to note that, as will be discussed later, all of them share a unique type of cofactor. 

Murphy Ml, LM Siegel, H Kamin (1973) Reduced nicotinamide adenine dinucleotide phosphate-sulfite reductase of enterobacteria. II. Identification of a new class of heme prosthetic group an iron-tetrahydroporphyrin (isobacteriochlorin type) with eight carboxylic acid groups. J Biol Chem 248 2801-3814. 

Johnson EF, B Mukhopadhyay (2005) A new type of sulfite reductase, a novel coenzyme F420 -dependent enzyme, from the methanarchaeon Methanocaldocccus jannaschii. J Biol Client 280 38776-38786. 

S. typhimurium enzyme (S94), which appears to be essentially identical to the E. coli sulfite reductase, are in agreement with the above results. Thus mutants lacking the flavoprotein or the hemoprotein component of the enzyme and containing only the appropriate partial activities have been obtained and the respective partial enzymes isolated. The absorption spectra of sulfite reductase preparations from the wild type and from these mutants are shown in Fig. 46, and the proposed structure for the two components of the wild-type enzyme is shown in Fig. 47. Reconstitution of NADPH-sulfite reductase by recombination of the flavoprotein... 

Fig. 46. Comparison of the absorption spectra of wild-type and mutant (cys G-439 and cys 1-68) sulfite reductases from Salmonella typhimurium. Spectra of S. typhi-murium sulfite reductase, cys G-439 NADPH-cytochrome e reductase, and cys 1-68 NADPH-oytoohrome c reductase, each dissolved in 0D5 M potassium phosphate buffer, pH 7.7, containing 0.1 mM EDTA, were read against a blank containing only buffer. The spectrum of each enzyme is presented in terms of its millimolar extinction coefficients, assuming 8 moles of flavin per mole of enzyme. Light broken line, calculated difference spectrum between those of wild-type and cys G enzymes when both enzyme solutions contain equal concentrations of flavin. From Siegel et al. (394).

Fio. 50. Schematic illustration of a tentative relationship between NADPH-sulfite reductase from the wild-type strain of Saccharomyces cerevisiae and two categories of MVH-sulfite reductases from various mutant strains. From Yoshimoto and Sato (.421). 

Bridged or Through-space Magnetically Coupled Complexes of High-spin Iron(III) Porphyrins with Other Types of Metal Complexes Possible Models for Cytochrome Oxidase, Assimilatory Sulfite Reductases, and Sulfite Oxidase... 

Mulkidjanian AY, Koonin EV, Makarova KS, Mekhedov SL, Sorokin A, Wolf YI, Dufresne A, Partensky F, Burd H, Kaznadzey D, Haselkom R, Galperin MY (2006) The cyanobacterial genome core and the origin of photosynthesis. Proc Natl Acad Sci USA 103 13126-13131 Murphy MJ, Siegel LM (1973) Siroheme and sirohydrochlorin. The basis for a new type of porphyrin-related prosthetic group common to both assimilatory and dissimilatory sulfite reductase. J Biol Chem 248 6911-6919... 

Sulfite reductases contain siroheme and iron-sulfur centers. Siroheme, also present in some nitrite reductases, is an iron tetrahydroporphyrin of the isobacteriochlorin type with eight carboxylic acid side-chains (Fig. 1). Siroheme isolated from Desulfovibrio species was found to be a monoamide, heptamethyl ester derivative, rather than the usual octamethyl ester derivative, which suggests that in these organisms an amidated form of the siroheme may be the physiologically active prosthetic group [93]. Sulfite reductases are divided into two classes, the assimilatory and the dissimilatory enzymes. The assimilatory sulfite reductases produce sulfide for use in the cell biosynthetic pathways. The dissimilatory enzymes are present in the sulfate-reducing organisms, and reduce sulfite as a respiratory substrate in a process coupled to ATP formation. 

Desulforubidin was purified from Desulfomicrobium baculatum Norway 4 [120] and DSM 1743 [113], and recently from Desulfosarcina variabilis [119]. This type of sulfite reductase is characterized by an absorption peak at 545 nm. Their molecular mass and subunit structure are very similar to that of de-sulfoviridins, and a y subunit has also been observed [119,121]. In contrast to desulfoviridin, the sirohemes are fully metallated. 

A number of different enzymes can carry out the reduction of nitrite to either ammonium or nitric oxide and/or nitrous oxide. The latter types are involved with the denitrification process (Payne, 1973) and will not be considered here. Among the enzymes that catalyze the six-electron reduction of nitrite to ammonia, several different types are recognized. These are (I) assimilatory NiRs that function in biosynthetic nitrate assimilation of higher plants, algae, and fungi, (2) ammonia-forming dissimilatory NiRs involved in anaerobic nitrate respiration of diverse bacteria, and (3) assimilatory and dissimilatory sulfite reductases... 

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