546 



A. P. Nygaard 



seen from the figure that both the original preparation and the stable enzyme 

 followed zero-order kinetics with cytochrome c as acceptor in the region 

 10"^ M to 10"* M when the phosphate concentration was very low (ji 0-01). 

 When the buffer concentration was increased to n 0-08, however, the activity 



CytcxWM — - 



Fig. 1 . The effect of the concentration of cytochrome c on the rate of oxidation 

 of lactate (dl, 002 m) by a crude preparation of LDH and by the heat- and 

 /7CMB-stable enzyme contained in this preparation; pH 71; 0001 m ethylene- 

 diamine tetra-acetate (EDTA) was added. 



AAA Original preparation, in phosphate buffer, /< 001 



+ + + Original preparation in phosphate buffer, /« 008 



• • • Heat- and/jCMB-stable enzyme, in phosphate buffer, /t 001 



O O O Heat- and/jCMB-stable enzyme, in phosphate buffer, /< 008 



Ordinate: arbitrary velocity units; values were calculated from AE at 550 m/<, using 

 £mM = 18-6. 



of the original enzyme was practically unaltered, whereas the stable enzyme 

 in this buffer followed first-order kinetics with respect to cytochrome c. The 

 ratio of rates of reduction of cytochrome cVferricyanide/2:6-dichlorophenol- 

 indophenol ('relative activities') was 12: 1 : 1 for the stable enzyme compared 

 with 0-8:1:1 for the original preparation. 



LDH I 



This reduced cytochrome c, ferricyanide, and indophenol at substantially 

 the same rate. The turnover number of a preparation was 6,000 moles 



