Electron-transfer flavoprotein from anaerobic Ascaris suum mitochondria and its role in NADH-dependent 2-methyl branched-chain enoyl-CoA reduction.

Electron-transfer flavoprotein was purified to apparent homogeneity from mitochondria of the parasitic nematode, Ascaris suum. The native molecular weight of the enzyme was 70,000, as estimated by gel filtration, and it migrated as two bands with apparent subunit molecular weights of 37,000 and 31,500 during sodium dodecylsulfate polyacrylamide gel electrophoresis. The enzyme exhibited an absorption coefficient for the bound FAD of 13.5 mM-1.cm-1 at 436 nm and a protein/flavin (270 nm/436 nm) ratio of 5.6. While the ascarid enzyme is similar to its mammalian counterpart, physiologically it functions in the reverse direction, shuttling reducing power from the electron-transport chain to a soluble 2-methyl branched-chain enoyl CoA reductase. Indeed, when A. suum submitochondrial particles were incubated with NADH, 2-methylcrotonyl-CoA and purified A. suum 2-methyl branched-chain enoyl-CoA reductase, 2-methylbutyryl-CoA formation was proportional to the amount of electron-transfer flavoprotein added.