Active synthesis of C24:5, n-3 fatty acid in retina.
The formation of 14C-labelled long-chain and very-long-chain (n-3) pentaenoic and hexaenoic fatty acids was studied in bovine retina by following the metabolism of. [14C]-docosapentaenoate [C22:5, n-3 fatty acid (22:5 n-3)], [14C]-docosahexaenoate (22:6 n-3), and [14C]acetate. With similar amounts of 22:5 n-3 and 22:6 n-3 as substrates, the former was actively transformed into 24:5 n-3, whereas the latter was virtually unmodified. Labelled 24:5, 26:5, 24:6 and 22:6 were formed from [1-14C]22:5 n-3, showing that pentaenoic fatty acids including 24:5 n-3 can be elongated and desaturated within the retina. When retinal microsomes were incubated with [1-14C]22:5 n-3, 24:5 n-3 was the only fatty acid formed. In retinas incubated with [14C]acetate, 24:5 n-3 was the most highly labelled fatty acid among the polyenes synthesized, 24:6 n-3 being a minor product. Such selectivity in the elongation of two fatty acids identical in length, 22:5 n-3 and 22:6 n-3, despite the fact that 22:5 is a minor and 22:6 a major fatty acid constituent of retina, suggests that the active formation of 24:5 n-3 plays a key role in n-3 polyunsaturated fatty acid (PUFA) metabolism. This compound might give rise to even longer pentaenes via elongation, and to the major PUFAs of retina, 22:6 n-3, by 6-desaturation and chain shortening. Of all retinal lipids, a minor component, triacylglycerol (TG), incorporated the largest amounts of [14C]22:5 and 22:6. TG also concentrated most of the [14C]24:5 formed in retina, whether from [14C]22:5 n-3 or from [14C]acetate, suggesting an important role for this lipid in supporting PUFA metabolism and the synthesis of 22:6 n-3.
Rotstein
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NP
Instituto de investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur and Consejo de investigaciones Científicas y Técnicas, Bahía Blanca, Argentina.
Pennacchiotti
G L
GL
Sprecher
H
H
Aveldaño
M I
MI
D000085:Acetates / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002250:Carbon Radioisotopes; D002417:Cattle; D002788:Cholesterol Esters / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism; D010743:Phospholipids / Q000302:isolation & purification / Q000378:metabolism*; D011865:Radioisotope Dilution Technique; D012160:Retina / Q000378:metabolism*; D013109:Sphingomyelins / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism
D000085:Acetates; D002250:Carbon Radioisotopes; D002788:Cholesterol Esters; D004075:Diglycerides; D005231:Fatty Acids, Unsaturated; D010712:Phosphatidic Acids; D010743:Phospholipids; D013109:Sphingomyelins; D014280:Triglycerides; D004281:Docosahexaenoic Acids; C026219:docosapentaenoic acid