Abstract
The anaerobic bacterium Megasphaera elsdenii uses lactate as the carbon source and produces lower fatty acids in the rumen of cattle and sheep. Electron-transferring flavoprotein (ETF) is a key enzyme in the intracellular redox system of M. elsdenii. ETF receives electrons from flavoprotein D-lactate dehydrogenase (D-LDH), which oxidizes D-lactate to pyruvate. The received electrons are then transferred to flavoprotein enoyl-CoA reductase (ECR), which reduces enoyl-CoA to acyl-CoA. The acyl-CoAs are eventually changed to fatty acids by CoA elimination. ETF also receives electrons from NADH, which is reduced by many other redox reactions. ETF contains two FAD molecules as the cofactor. The functions of the two FAD molecules are presently unlcear. In this study, we found the followings by spectrophotometric experiments using purified flavoproteins. Here the two FAD molecules in ETF are designated FAD-1 and FAD-2. (1) NADH reduces both FAD-1 and FAD-2. (2) D-LDH interacts with only FAD-1. (3) ECR interacts with both FAD-1 and FAD-2. (4) Electron transfer between FAD-1 and FAD-2 can occur without NADH/NAD+, D-LDH, and ECR. [J Physiol Sci. 2006;56 Suppl:S121]
