The oxidation of methylglyoxal by mammalian pyruvate dehydrogenase

Mammalian pyruvate dehydrogenase actively catalyzed the oxidation of methylglyoxal to acetyl-CoA. The reaction was fully enzymatic with an estimated Km of 1.89 mM. On the other hand, methylglyoxal was a competitive inhibitor of the enzyme for pyruvate, the Ki being in the 1 mM range. The reaction was inhibited in the presence of HgCl2. The reaction products were quantitatively identified as acetyl-CoA and formic acid. A mechanism for the reaction is proposed.     

The pyruvate branch point in fish liver mitochondria: Effects of acylcarnitine oxidation on pyruvate dehydrogenase and pyruvate carboxylase activities

Summary Palmitoyldl-carnitine inhibits¹⁴CO₂ production from 1-[¹⁴C]-pyruvate and from 1-[¹⁴C]-alanine by mitochondria from rainbow trout liver. The inhibitory effect occurs in both respiratory states III and IV. Fixation of H¹⁴CO ₃ ^– into acid-stable products by intact mitochondria requires pyruvate and ATP and is inhibited by sodium arsenite. This inhibitory effect is completely abolished by acetyldl-carnitine. It is proposed that under these conditions, oxidation of palmitoyldl-carnitine results in inhibition of pyruvate dehydrogenase while oxidation of acetyldl-carnitine results in activation of pyruvate carboxylase in intact rainbow trout liver mitochondria.