94 



1. lODOACETATE AND lODOACETAMIDE 



observed that 1 m.M iodoacetate completely prevents the respiratory stim- 

 ulation by pyruvate in rat ventricle slices. The most complete study of 

 the heart was done by Miller and Olson (1954), using duck ventricle slices. 

 The results are similar to those in CJilorella, in that the uptake of pyruvate 

 and lactate is quite sensitive, being depressed by 0.01 mM or lower iodo- 

 acetate, whereas the respiration is inhibited by concentrations around 1 mM 

 (Fig. 1-9). Since the uptake of pyruvate can be inhibited 66% before an 



Fig. 1-9. Effects of iodoacetate on pyruvate 



and lactate metabolism in duck heart slices. 



Q is given as /<liters/mg dry weight/hr. (From 



Miller and Olson. 1954.) 



effect on respiration is observed, the authors suggested that another path- 

 way for pyruvate metabolism, more sensitive than respiration to iodoace- 

 tate, is operative. This might be a reversal of the EM pathway toward 

 3-phosphoglyceraldehyde. Such an explanation may well apply to CJilorella. 

 The oxidation of pyruvate by a rat brain suspension is gradually depressed 

 by iodoacetate: 0.27 mM inhibits little during the first hour but after 5 hr 

 the inhibition is nearly complete, while 3.2 mM inhibits completely in 2 hr, 

 the effect on lactate oxidation being very similar (Bernheim and Bernheim, 

 1941). In electrically stimulated guinea pig brain slices, the Og uptake with 

 lactate as the substrate is not inhibited by iodoacetate until a concentration 

 of around 0.08 vclM is reached, whereas the respiration with glucose is al- 

 ready depressed at 0.01 mM (Heald, 1953). Thus in this tissue, although 

 lactate oxidation is quite sensitive to iodoacetate, it would be possible to 



