530 



E. BOERI AND M. RiPPA 



The latter reaction is followed in this instance, as it appears from Table 1. 

 One mole of oxygen is consumed for two molecules of lactate disappearing, 

 and for two molecules of pyruvate formed. 



The Effect of Metals 



Certain metals were found to affect the autoxidation rate. Copper and 

 iron were found to possess the most evident influence. Figure 9 shows their 



Asymptote 



Fig. 9. The effect of the addition of metals on the autoxidation rate. Abscissa: 

 time in minutes. Ordinate: /<!. of oxygen consumed. No. 1 : no addition. No. 2: 

 in the presence of 01 niM FeCla- No. 3 : in the presence of 01 mM FeSOi. No. 4: 

 in the presence of 0- 1 mM FeS04 and 0- 1 mM o-phenanthroline. No. 5 : in the 

 presence of 0-1 mM FeS04 and 0-3 mM o-phenanthroline. No. 6: in the presence 

 of 0-1 mM CUSO4. Enzyme added: 17m//moles. Gas phase: oxygen. The line 

 marked 'asymptote' corresponds to the theoretical consumption for the autoxi- 

 dation of the lactate present. pH 6 was obtained by addition of diluted acetic acid 

 and sodium hydroxide, and controlled before and after the incubation at 37''C. 



action. Copper inhibits strongly the autoxidation. Ferrous and ferric iron 

 instead promote it. Ferrous ions have a more marked effect. 



In view of this effect, o-phenanthroline was tested. Strangely enough, it 

 was found that the combination of equimolar amounts of o-phenanthroline 

 and ferrous ions had a stimulating effect which was even higher than that of 

 ferrous ions alone. When, instead, o-phenanthroline was added in a ratio 3: 1 

 to the amount of ferrous iron, the effect on the autoxidation rate was lower 

 than with ferrous ions alone, but it was still evident. 



When now the effect of the substrate concentration (lactate) was reinvesti- 

 gated in the presence of excess of ferrous iron, the inhibiting effect of high 



