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Nitritreduktasen sind Schlüsselenzyme im biogeochemischen Stickstoffkreislauf und katalysieren die sechs-Elektronen-Reduktion von Nitrit zu Ammoniak innerhalb des Stoffwechselwegs der dissimilatorischen Nitratreduktion zu Ammoniak. Ziel dieser Arbeit war es, die Cytochrom c Nitritreduktase des sulfatreduzierenden Bakteriums Desulfovibrio desulfuricans (ATCC 27774) zu reinigen sowie biochemisch und spektroskopisch zu charakterisieren. Hierzu wurde D. desulfuricans mit Nitrit als terminalem Elektronenakzeptor und DL-Lactat als Elektronendonor kultiviert. Die membranständige Cytochrom c Nitritreduktase wurde in drei chromatographischen Schritten zur Homogenität gereinigt. Das Enzym ist ein Heterodimer mit einer molekularen Masse von 60,4 kDa der großen Untereinheit und von 17,5 kDa der kleinen Untereinheit. Das Elektronenanregungsspektrum zeigt Signale die charakteristisch für c-Typ Cytochrome sind. Im EPR Spektrum erkennt man Signale von low-spin Häm-Fe(III) Zentren. Durch Edmanabbau wurden die ersten sieben Aminosäuren des aminoterminalen Endes der Aminosäuresequenz der Nitritreduktase ermittelt.

Tolerance and adaptation to heavy metals of Desulfovibrio- and Desulfotomaculum-strains of different origin have been investigated in enrichment cultures under different conditions of sulphate supply. Three groups of low, medium, and high toxicity were found with As, V, and Mo in the first, Ni, Sb, Co, and Hg in the second, and Cd, Zn, U, and Cu in the third group. If the SO"4-supply was restricted to heavy metal sulphates with a relation of 1:1 of heavy metal- and SO"4 -ions (2:3 with Sb2(SO4)3) the tolerance was somewhat lowered. Adaptation to higher concentrations of heavy metals was possible, if the strains had not yet been exposed and adapted to higher concentration levels at their natural habitats. The tolerance range of desulfurizers has been compared with the tolerance range of different biochemical types of microorganisms.

Hexacyanoferrat-compounds are suitable 1. to indicate the valence of Fe-ions in cultures of desulfuricants (Desulfovibrio spec., Desulfotomaculum) in fluid and solid medium before and after inoculation; 2. stain directly the sulfate-reducing bacteria in presence of Fe-ions and give a colour-reaction of those parts of the cell containing Fe-compounds, e.g. FeS. Therefore they act as a cytochemical indicator system. The chemical base of the reactions are as follows: (1) 4HS + SO42 leads to H2S + 2H2O + OH- H2S leads to H+ + HS- leads to 2H+ + S2- (in the bacteria) (2) FeIII-salt + S2-leads to Fe2S3 leads to 2FeIIS + S 2FeIIS + FeIII(CN6) leads to FeIIIFeII(CN)6 (blue complex-compound).

Hexacyanoferrate-compounds are suitable to indicate the efficacy of antimicrobial substances to sulfate-reducing bacteria. They act as a cytochemical indicator system. (Stübner, 9), e. g. K3FeIII(CN)6 showes FeS formation before any visible blackening of the medium. By using hexacyanoferrate compounds it is easier to determine the efficacy of antimicrobial agents. In addition a microscopical control is recommended to detect damaged or avital bacteria in the limiting concentrations of the agents.