526 



E. BOERI AND M. RiPPA 



Effect of the Concentration of Lactate 



L(+)-Lactate is the specific substrate. There was no oxygen consumption 

 without addition of lactate. Equally, no oxygen consumption was found in 

 the absence of the enzyme. It is known that when ferricytochrome c or 



/ o 

 o / 



5 10 15 20 



/2 m moles 



Fig. 1. The eflect of the concentration of flavocytochrome b.y on the oxidation of 

 lactate by oxygen. Abscissa: m/mioles of enzyme in the Warburg vessel. 

 Ordinate: //I. of oxygen consumed in 15 min at 37 C, 120 strokes/min. Phosphate 

 buffer, 001 m, pH 6. Lactate concentration 0002 m. Enzyme added at time zero 

 from the side arm. Gas phase: oxygen. 



ferricyanide is used as the oxidant, the velocity increases with increasing 

 lactate concentration up to a saturation value, these curves allowing cal- 

 culation of the MichaeUs constant. When instead oxygen was the oxidant, a 

 clear inhibiting effect of the substrate was seen, as it appears from Fig. 2. 



/ \ 



/ -Ok. 



logdactnte) 



Fig. 2. The effect of the concentration of L(+)-lactate. Abscissa: logarithm of 



themolarity of lactate. Ordinate: oxygen consumption in 25 min. Enzyme added: 



3-75 m/«moles. Total volume: 31 ml. Other conditions as in Fig. 1. 



