Probable short and branched chain specific acyl-CoA dehydrogenase that catalyzes the removal of one hydrogen from C-2 and C-3 of the fatty acyl-CoA thioester, resulting in the formation of trans-2-enoyl-CoA. 2-methylbutanoyl-CoA + H(+) + oxidized [electron-transfer flavoprotein] = (2E)-2-methylbut-2-enoyl-CoA + reduced [electron-transfer flavoprotein] Lipid metabolism; mitochondrial fatty acid beta-oxidation. Amino-acid degradation; L-isoleucine degradation. Homotetramer. Belongs to the acyl-CoA dehydrogenase family.