Catalyzes the oxidative decarboxylation of glutaryl-CoA to crotonyl-CoA and CO(2) in the degradative pathway of L-lysine, L-hydroxylysine, and L-tryptophan metabolism. It uses electron transfer flavoprotein as its electron acceptor. glutaryl-CoA + 2 H(+) + oxidized [electron-transfer flavoprotein] = (2E)-butenoyl-CoA + CO2 + reduced [electron-transfer flavoprotein] Amino-acid metabolism; lysine degradation. Amino-acid metabolism; tryptophan metabolism. Homotetramer. Belongs to the acyl-CoA dehydrogenase family.