404 



F. Egami, M. Ishimoto and S. Taniguchi 

 Table 14. Reduction of 3 '-phospho-adenosine-5 '-phosphate 



Reaction mixture contained 60 /imoles of phosphate buffer, pH 7-2, 50 //moles of NaF, 1 //mole of 



meihylviologen and 05 ml of crude extract in total volume of 1-8 ml. Centre wells contained 0-2 ml of 



2NNaOH. Gas phase: hydrogen. Temperature: 30°C. 



Intermediary formation of APS by the consumption of ATP in the course 

 of sulphate reduction may be conceived to elevate the oxido-reduction 

 potential of the system, sulphate-sulphite, above that of cytochrome C3 

 (Table 15). 



Table 15. Oxidation-reduction potential of acids of sulphur 



Effectj)/ Cytochrome C3 on Sulphate Reduction 



In the reduction of sulphate in the presence of ATP as well as in the 

 reduction of APS, omission of methylviologen from the reaction mixture 

 retarded the reaction, especially when extracts deprived of cytochrome Cg 

 by passage through a column of cation-exchanger (Amberlite IRC50) were 

 employed as enzyme solutions. The addition of cytochrome c^ to the 

 solution stimulated the hydrogen uptake in the case of sulphate reduction in 

 the presence of ATP as well as in the case of APS reduction. Similar results 

 were obtained with partially-purified enzyme, which reduced APS to sulphite, 

 in the presence of hydrogenase. Mammahan cytochrome c was quite in- 

 effective. These results (Table 16) indicate the indispensable roles of the cyto- 

 chrome C3 as an electron carrier in the reduction of APS to sulphite as well 

 as in the reduction of sulphite to thiosulphate (Ishimoto et al, 1957, 1958). 



