Fatty acid metabolism studies of human epidermal cell cultures.
Adult human epidermal keratinocytes grow rapidly in medium that is essential fatty acid (EFA)-deficient. In this medium they exhibit decreased amounts of the fatty acids, 18:2, 20:3, 20:4, and contain increased amounts of monounsaturated fatty acids. [14C]- and [3H]acetate and radiolabeled fatty acids, 16:0, 18:2, and 20:4 were used to study the fatty acid metabolism of these cells. Label from acetate appeared in 14- to 20-carbon fatty acids, both saturated and monounsaturated. No label was seen in the essential fatty acid 18:2, 18:3, and 20:4. Radiolabel from [9, 10-3H]palmitic acid (16:0) was detected in 16:0, 16:1, 18:0, and 18:1. [14C]linoleic acid (18:2) was converted to 18:3, 20:2, 20:3, and 20:4, demonstrating delta 6 and delta 5 desaturase activity in keratinocytes. Label from acetate, 16:0, or 18:2 was found mostly in the cellular phospholipids while only one third of the label from [14C]arachidonic was found in the phospholipids. [14C]acetate and [14C]18:2 time course data were used to construct a model of the metabolism of these reactants, using coupled, first-order differential equations. The data show that EFA-deficient keratinocytes metabolize fatty acids using pathways previously found in liver; they suggest the positioning of 18:2 desaturase and 18:3 elongase near the plasma membrane; they indicate that for the synthesis of nonessential fatty acids the formation of 18:0 from 16:0 is the rate-determining step; and they show that the conversion of 18:2 to 20:3 is rapid. These experiments demonstrate a method to study lipid enzyme kinetics in living cells.
Marcelo
C L
CL
Department of Dermatology, University of Michigan Medical School, Ann Arbor 48109-0528.
Dunham
W R
WR
D000085:Acetates / Q000378:metabolism; D016718:Arachidonic Acid / Q000378:metabolism; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D044943:Fatty Acid Desaturases / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism*; D007700:Kinetics; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000378:metabolism; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D014316:Tritium
D000085:Acetates; D002250:Carbon Radioisotopes; D005227:Fatty Acids; D008041:Linoleic Acids; D010169:Palmitic Acids; D014316:Tritium; D016718:Arachidonic Acid; D019308:Palmitic Acid; D019787:Linoleic Acid; D044943:Fatty Acid Desaturases