Cytochrome Cg 413 



Table 3. Activity of sulphite reductase preparations 



Experiments were conducted in conventional Warburg manometers under hydrogen gas at ZTC in 

 0-5°^KHjPO4(pH 6-9) with CdClj in centre well. Negative (?h2 values for Na.jSOj recorded (in //I H3 

 absorbed/mg N/hr) from five experiments. 



* A and B represent further fractions from the soluble fraction, one (A) soluble 

 in 0-5 saturated (NH4)2S04, the other {B) not. 



t Q values of fractions refer to the N content of the original un fractionated 

 material. 



J ATP (sodium salt) and acetyl phosphate (lithium salt) 70 /tg of each/ml. 



In addition, 'energy-rich' phosphate may be used in the primary activation 

 of sulphite. 



Reduction of Sulphate 



The most obvious function of cytochrome Cg, that of being a co-factor in 

 the reduction of sulphate, is the furthest from being established experimentally 

 (Note 1). The reasons for beheving that cytochrome c^ has such a function 

 are four: 



1. It is a priori hkely that anaerobic sulphate reduction would involve an 

 electron transport system analogous to the reduction of oxygen or 

 nitrate. Cytochrome c^ is present in all strains of D. de sulphur icans and 

 haematins are to be found in the other well-authenticated sulphate- 

 reducing bacteria; these facts suggest that haematins are universally 

 involved in this biochemical process. 



2. Anaerobic oxidation of intracellular cytochrome c^ by sulphate can 

 be observed with proper precautions. This reaction is inhibited by 

 known specific inhibitors of sulphate reduction (selenate, mono- 

 fluorophosphate). 



3. Cells starved of inorganic iron are deficient in cytochrome c.^, and in 

 ability to reduce sulphate. They can, in fact, only grow by the fermenta- 

 tive reaction (4) above and hence are only obtainable in pyruvate media. 



