Studies with general acyl-CoA dehydrogenase from pig kidney : inactivation by a novel type of "suicide" inhibitor, 3,4-pentadienoyl-CoA

Abstract

3,4-Pentadienoyl-CoA, an allenic substrate analog, is a potent inhibitor of the flavoprotein pig-kidney general acyl-CoA dehydrogenase. The analog reacts very rapidly (k = 2.4 x 103 min -1) with the native oxidized enzyme to form a covalent flavin adduct probably involving the isoalloxazine position N-5. This species is inactive, but activity may be regained by two pathways. The allenic thioester can be displaced (k = 0.3 min - 1) by a large excess of octanoyl-CoA substrate upon reversal of covalent adduct formation. Alternatively, the enzyme inactivator adduct slowly decomposes (t 111 = 75 min) to form the strongly thermodynamically favoured 2,4-diene and catalytically active, oxidized enzyme. During this latter process 15-20% of the activity is irreversibly lost probably due to covalent modification of the protein. These data suggest that 3,4-pentadienoyl-CoA should be considered a suicide substrate of the acyl-CoA dehydrogenase. The mechanism of the reactions, and in particular the 3,4->2,4 tautomerization, are consistent with a catalytic sequence initiated by abstraction of an a-hydrogen as a proton.