title: LC-PUFA biosynthesis in rainbow trout is substrate limited: use of the whole body fatty acid balance method and different 18:3n-3/18:2n-6 ratios.
abstract: Five experimental diets with constant total C(18) PUFA and varying 18:3n-3/18:2n-6 ratios were fed to rainbow trout over an entire production cycle. The whole-body fatty acid balance method demonstrated a clear trend of progressively reduced fatty acid bioconversion activity along the n-3 and n-6 pathways, up to the production of 20:5n-3 and 20:4n-6, respectively. This suggests that the pathway exhibits a "funnel like" progression of activity rather than the existence of a single rate limiting step. The production of 22:5n-3 and 22:6n-3 was more active than that of 20:5n-3. However, despite this trend in reduced apparent in vivo net enzyme activity, the efficiency of the various bioconversion steps (measured as % of bioconverted substrate) confirmed an opposing trend. A 3.2-fold higher Δ-6 desaturase affinity towards 18:3n-3 over 18:2n-6 and an 8-fold greater Δ-5 desaturase affinity towards 20:4n-3 over 20:3n-6 were recorded. The main results of the study were that (1) rainbow trout are quite efficient at bioconverting 18:3n-3 to 22:6n-3, and (2) the LC-PUFA biosynthetic pathway is substrate limited. Fillet n-3 LC-PUFA concentrations increased with the increasing dietary supply of 18:3n-3. Despite an almost identical dietary supply of n-3 LC-PUFA, originating from the fish meal fraction of the diets, the fillets of trout fed the diet richest in 18:3n-3 were 2-fold higher in n-3 LC-PUFA than fish fed low 18:3n-3 diets. Nevertheless, fillets of trout fed a fish oil control diet contained more than double the amount of n-3 LC-PUFA compared to fish fed the diets richest in 18:3n-3.
authors: School of Life and Environmental Sciences, Deakin University, Warrnambool, VIC, Australia.
authors: T
authors: T
authors: Thanuthong
authors: D S
authors: DS
authors: Francis
authors: S P S D
authors: SP
authors: Senadheera
authors: P L
authors: PL
authors: Jones
authors: G M
authors: GM
authors: Turchini
mesh_terms: D000821:Animal Feed; D000818:Animals; D001711:Biotransformation; D002849:Chromatography, Gas; D000090943:Delta-5 Fatty Acid Desaturase; D044943:Fatty Acid Desaturases / Q000378:metabolism; D015525:Fatty Acids, Omega-3 / Q000378:metabolism*; D043371:Fatty Acids, Omega-6 / Q000378:metabolism*; D005395:Fish Oils / Q000008:administration & dosage / Q000378:metabolism*; D050602:Linoleoyl-CoA Desaturase / Q000378:metabolism; D008043:Linseed Oil / Q000008:administration & dosage / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D010938:Plant Oils / Q000008:administration & dosage / Q000378:metabolism*; D000074242:Sunflower Oil
chemical_list: D000090943:Delta-5 Fatty Acid Desaturase; D015525:Fatty Acids, Omega-3; D043371:Fatty Acids, Omega-6; D005395:Fish Oils; D010938:Plant Oils; D000074242:Sunflower Oil; D008043:Linseed Oil; D044943:Fatty Acid Desaturases; D050602:Linoleoyl-CoA Desaturase