METABOLISM OF MALONATE 



229 



is oxidized but the R.Q. is 1.47, close to that for complete oxidation to 

 CO2 and water. Again, no decarboxylation is observed in nitrogen. Horio 

 and Okunuki (1954) reported a 30-60 min lag period for Mycobacterium and 

 also found that decarboxylation presumably precedes oxidation, because 

 CO2 formation always is ahead of Oo uptake, and acetate can be demon- 

 strated in the culture after 2 hr. The explanation of this behavior is found 

 in the work of Gray (1952) on Pseudomonas. Unadapted cells show a lag 

 period of 2 hr whereas cells cultured for 70 hr in 22 mM malonate are able 

 to oxidize malonate immediately (Fig. 1-21). It was postulated that mal- 



Time ( hours) 



Fig. 1-21. Oxidation of malonate by normal and 

 adapted Pseudomonas aeruginosa. (From Gray, 1952.) 



onate decarboxylase is an adaptive enzyme, and it was pointed out that 

 the resistance of certain microorganisms to malonate may be due to such 

 an enzyme as well as to permeability barriers. Horio and Okunuki showed 

 that streptomycin does not directly inhibit the decarboxylation of mal- 

 onate or the oxidation of acetate, but inhibits malonate oxidation in un- 

 adapted cells, probably by preventing the synthesis of the decarboxylase. 

 The oxygen requirement may also relate to the adaptive enzyme syn- 

 thesis. 



