Specificity in Ceramide Biosynthesis from Long Chain Bases and Various Fatty Acyl Coenzyme A's by Brain Microsomes

Abstract

The formation of ceramide from long chain bases and W-acyl coenzyme A's by a mouse brain microsomal preparation was investigated.Activity of the acyl-CoA:long chain base N-acyltransferase was measured as a function of time, acyl-CoA concentration, amount of amine, and microsomal protein concentration.The rate and extent of conversion of stearoyl-, lignoceroyl-, palmitoyl-, and oleoyl-CoA to ceramide were in the ratio of about 60:12:3:1, respectively.Since this ratio strongly resembles the relative distribution of these fatty acids in brain sphingolipids, we suggest that the transferase plays an important role in controlling the observed distribution.There was some specscity with respect to the base, particularly with lignoceroyl-CoA, which reacted somewhat better with dihydrosphingosine than with sphingosine.The keto analogue of dihydrosphingosine acted as an acceptor, with stearoyl-CoA, to form "ketoceramide."The microsomal preparation also converted the acyl-CoAs to free fatty acid and polar lipid during the incubations.Ceramide synthesis was found to occur primarily in microsomal membranes, but ceramide hydrolase was rather widely distributed in subcellular fractions; its highest specific activity was in the lysosome-rich fractions.Free stearic acid did not react to form ceramide, yet it could react with ethanolamine to form the analogous amide.From these and related considerations, we conclude that the synthetic capability of ceramide hydrolase has little or no physiological significance.