402 



F. EgAMI, M. ISHIMOTO AND S. TaNIGUCHI 



acid-am mooia and propanol-ammonia) were employed (Ishimoto and 

 Fujimoto, 1959). 



Table 11. Sulphate reduction in the presence of ATP 



Reaction mixfore in Warburg vessels contained 50 //moles of Tris buffer, pvH 7-4, 28 //moles of 



NaF. 1 //mole of melhylviologen and crude extracts of sulphate-reducing bacteria in total volume of 



1-4 ml. Centre wells contained 0-2 ml of 2 N NaOH. Gas phase: hydrogen. Temperature: 30"C. 



Synthetic APS (Baddiley, Buchanan and Letters, 1957) was reduced in 

 similar conditions but without ATP. The ratio of hydrogen uptake and 

 development of hydrogen sulphide was 4: 1 (Table 12). 



Table 12. Reduction of adenosine-5'-phosphosulphate 



Reaction mixture in Warburg vessels contained 50 /(moles of Tris buffer, pH 7-0, 1 /*mole of 



methylviologen, 0-2 ml of crude extracts and 1 -64 //moles of APS in a total volume of 09 ml. Centre 



wells contained 2 ml of 2 n NaOH. Gas phase: hydrogen. Tem.perature : 30°C. Control vessel 



was wiLhout APS. 



Experiment 



Control 



Difference 



APS added 

 (/tmoles) 



1-64 

 



Hydrogen uptake HgS formed 

 (//moles) (/tmoles) 



1-21 

 0-13 

 1-08 



The disappearance of APS and formation of adenyUc acid was demonstrated 

 by paper electrophoresis and by paper chromatography. These results 

 indicate the pathway of sulphate in the reduction as follows (Ishimoto and 

 Fujimoto, 1959): 



SO^- + ATP = APS + 2Pi (or PP) by sulphurylase 



APS + 2e = AMP + SO3-- by APS reductase 



SO3 + 3H2 = S"- + 3H2O by sulphite reducing system. 



Ihe intermediary formation of sulphite was shown by the inhibitory 

 experiments with arsenite (O-OOl m), a strong inhibitor for sulphite reductase. 



