Abstract
Serine palmitoyltransferase [EC 2.3.1.50] catalyzes the first unique reaction of sphingolipid biosynthesis. To determine whether or not different rat tissues are capable of initiating this pathway, its activity was determined for microsomes from rat liver, lung, brain, kidney, intestine, spleen, muscle, heart, pancreas, testes, ovary, and stomach. Serine palmitoyltransferase was found in every tissue, and, when compared to the microsomal glycerol 3-phosphate acyltransferase, the activities correlated directly with their sphingomyelin levels as a percentage of total phospholipids. This suggests that the activities were comparable to expected cellular needs for long-chain bases, if the initial enzymes of glycerolipid and sphingolipid biosynthesis influence the phospholipid composition of cells by determining the relative partitioning of fatty acyl-CoA's toward these two lipid classes. Serine palmitoyltransferase activities were also determined using different fatty acyl-CoA's and were consistently greatest with CoA thioesters of saturated fatty acids with 16 +/- 1 carbon atoms. This suggests that the predominance of 18-carbon long-chain bases in vivo is due to the higher activity of this enzyme with palmitoyl-CoA. Together, these findings indicate a role for serine palmitoyltransferase in regulating both the type and amount of long-chain bases found in tissues.
Highlights
Serinepalmitoyltransferase[EC 2.3.1.501catalyzes and a fatty acid is added to the 2-position in amide linkthe first unique reaction of sphingolipid biosynthesis
Sphinganine, and phytosphingosine, smaller amounts of homologous compounds influence the phospholipid composition of cellsby determining with 16 to 22 carbon atomsexist [13] and this entire group the relative partitioninogf fatty acyl-CoA's toward these two lipid classes.Serinepalmitoyltransferaseactivitieswerealsodeter
In many samples a small fraction of the total radiolabel migrated near the solvent front [6, 20] or coincident with the sphinganine and sphingosine standards, Microsomes from lung, pancreas, and testes produced a compound that migrated slightly abovethe origin and was probably phosphatidylserine
Summary
Microsomes from every rat tissue examined catalyzed the formation of 3-ketosphinganine from [3H]serine and palmitoyl-CoA (Fig. 1; chromatographic data for liver and brain arenot shown because they have been reported previously in refs. 6 and 17). Microsomes from every rat tissue examined catalyzed the formation of 3-ketosphinganine from [3H]serine and palmitoyl-CoA In many samples a small fraction of the total radiolabel migrated near the solvent front (a common artifact with 3-ketosphinganine) [6, 20] or coincident with the sphinganine and sphingosine standards, Microsomes from lung, pancreas, and testes produced a compound that migrated slightly abovethe origin and was probably phosphatidylserine. Measurements of total activities using tissue homogenates were not successful, probably due to greater
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