Analysis of the condensation step in elongation of very-long-chain saturated and tetraenoic fatty acyl-CoAs in swine cerebral microsomes.

The condensation products in the elongation of exogenous arachidoyl-CoA (20:0-CoA) and endogenous fatty acids in adult swine cerebral microsomes were isolated and purified by using HPLC and a radioanalyzer. A saponification product of the condensation reaction of 20:0-CoA with malonyl-CoA was identified by gas chromatography-mass spectrometry as 2-heneicosanone (21:0-2-one). The endogenous substrates (16:0-CoA and 20:4-CoA) were likewise identified as 2-heptadecanone (17:0-2-one) and 2-heneicosatetraenone (21:4-2-one). Quantitative analysis of condensation activity was performed using electron-impact mass fragmentography. A characteristic fragment ion (m/z 59) of 21:0-2-one was used to estimate the condensation activity for 20:0-CoA, and fragment ions at m/z 58 and 80 were monitored for the endogenous substrates (16:0-CoA and 20:4-CoA, respectively). The molecular ion for each product was detected using chemical ionization. A comparative study of the condensation of 20:0-CoA and endogenous substrates was carried out for microsomes obtained from white matter, gray matter, and isolated neuronal cells; the activity for 20:0-CoA was significantly lower in gray matter and neuronal cells than in white matter, whereas the activity for endogenous substrates was almost the same for microsomes obtained from gray and white matter. This result suggests that the condensation enzyme for 20:0-CoA may be different from that for endogenous 16:0-CoA or 20:4-CoA in swine cerebral microsomes.