Various Forms of Yeast Lactate Dehydrogenase 



549 



on the other hand, was strongly affected by salts; the affinity for cytochrome 

 c was decreased by increased salt concentration. Figure 2 shows the reaction 

 properties of LDH III in three different solutions. In phosphate, // 001, the 

 enzyme followed zero-order kinetics at least down to 10"^ m; in phosphate, 

 fj, 008, the reaction was of first-order up to a concentration of 10^ m cyto- 

 chrome c. The addition of NaCl (0-04 m) decreased the first-order rate 



Fig. 4. Tlie rate of tlie reduction of cytochrome c (2 x 10^^ m) by LDH II and 

 III as a function of pH (oL-Iactate, 002 m). 



• • • LDH III in 0002 m phospliate + 0-002 m glycyiglycine 



+ + + LDH III in phosphate /i 008 + 0002 m glycyiglycine + 0001 m 



versene 

 AAA LDH 11 in phosphate /< 0008 -|- 0001 m versene, below pH 7-7; in 



glycyiglycine, 005 m, from pH 7-7 to 8-6; in glycine, 0-05 m, from 



pH 8-6 to 9-7. Change in the buffer at pH 8-6 and 7-7 did not affect 



the activity. 



Ordinate: arbitrary velocity units. 



constant. Figure 3 illustrates the fact that the same salt dependency exists at 

 pH 7-9. The sodium salts of chloride, sulphate, and acetate had much 

 stronger effects than Na-glycylglycinate. The pH-dependency curves of 

 LDH II and III with cytochrome c as acceptor were slightly different. This is 

 shown in Fig. 4. 



The reaction of LDH II and III with ferricyanide as acceptor was of zero- 

 order at least down to a concentration of 2 x 10^^ m, and the reaction with 

 indophenol attained half-maximal activity with 3 x 10 ^ m. Both enzymes 

 were unaffected by great variations in the salt concentration. The effect of 

 pH on the activity of LDH II and III with ferricyanide as acceptor is shown 



