Some characteristics of a chromophoric lipid associated with nitric oxide reductase from Paracoccus denitrificans

A lipid with a UV chromophore (lambda max = 274 nm) was purified in small amounts from nitric oxide reductase of Paracoccus denitrificans and determined to have a molecular weight of 686, a most probable formula of C43H78O4N2 and about two phenylhydrazine-reactive carbonyls. On the basis of 1H and 13C-NMR, IR and mass spectrometric studies, the chromophoric lipid was inferred to have something like bilateral symmetry and to contain ketone-like carbonyls, alkene centers and at least three alkyl or olefinic chains. Several likely substructures are discussed and an enaminoketone is considered as a model for the chromophore. Evidence was lacking for phosphate, an aromatic ring, a 1,4-quinone, polyunsaturated fatty acyl groups, isoprenyl/isopranyl chains and simple alkyl acids, esters, amides and ethers. The compound appears to have some novel features. On the basis of reconstitution studies, the chromophoric lipid may be essential for nitric oxide reductase activity.