Biochemical subnetworks identified by the GGM. Line widths correspond to partial correlation coefficients. A: Elongation and desaturation signatures, most likely mediated by ELOVL6 and SCD, for C16 and C18 fatty acids incorporated in lyso-PCs and sphingomyelins. B: Top: Diacyl-phosphatidylcholine (PC aa) species with elongation and peroxisomal β-oxidation associations. Several combinatorial variants of side chain compositions are possible for C36:4 and C38:4, and thus different enzymes could mediate this connection. Bottom: Alkyl-acyl-phosphatidylcholines (PC ae) with supposedly distinct side chain composition, giving rise to a low association with a directly connected species (C36:2). C: Recovered β-oxidation pathway from C18 down to C4. Four enzymes with overlapping substrate specificities catalyze the rate-limiting reactions of this pathway. D: Two high-scoring triads, where metabolite pairs with a pathway distance of two constitute strong partial correlations. This feature of partial correlations aids in the reconstruction of the network topology beyond the direct neighborhood of each metabolite.