Alternative route for the biosynthesis of polyunsaturated fatty acids in K562 cells

Abstract

K562 human leukaemia cells lack a significant Δ6-desaturase activity. However, they synthesize long-chain polyunsaturated fatty acids (PUFA) from linoleic (C(18:2(9,12))) and linolenic (C(18:3(9,12,15))) acids, by reactions involving a C2 chain elongation followed by a Δ5-desaturation step and, to some extent, a further elongation. The main products formed were separated by argentation t.l.c. and identified by g.l.c. as the uncommon fatty acids C(20:3(5,11,14)) and C(20:4(5,11,14,17)), respectively. These acids were also produced when cells were supplemented with C(20:2(11,14)) or C(20:3(11,14,17)) respectively The presence of a Δ5-desaturase was further confirmed by using its corresponding normal substrates, C(20:3(8,11,14)) and C(20:4(8,11,14,17)) which led to C(20:4(5,8,11,14)) and C(20:5(5,8,11,14,17)) respectively. On the other hand, a high Δ9-desaturase activity, but no significant Δ4-desaturase activity, were detected in K562 cells. These results indicate the existence of an alternative pathway, involving Δ5-desaturase, which is the only route for PUFA biosynthesis in K562 cells. This pathway may be relevant for the biosynthesis of PUFA in cells lacking Δ6-desaturase activity.