A novel method for the measurement of in vitro fatty acid 2-hydroxylase activity by gas chromatography-mass spectrometry

Fatty acid 2-hydroxylase (FA2H), encoded by the FA2H gene, is an enzyme responsible for the de novo synthesis of sphingolipids containing 2-hydroxy fatty acids. 2-Hydroxy sphingolipids are highly abundant in the brain, as major myelin galactolipids (galactosylceramide and sulfatide) contain a uniquely high proportion (similar to 50%) of 2-hydroxy fatty acids. Other tissues, such as epidermis, epithelia of the digestive tract, and certain cancers, also contain 2-hydroxy sphingolipids. The physiological significance of the 2-hydroxylation on N-acyl chains of subsets of sphingolipids is poorly understood. To study the roles of FA2H and 2-hydroxy sphingolipids in various tissues, we developed a highly sensitive in vitro FA2H assay. FA2H-dependent fatty acid 2-hydroxylation requires an electron transfer system, which was reconstituted in vitro with an NADPH regeneration system and purified NADPH: cytochrome P-450 reductase. A substrate [3,3,5,5-D-4] tetracosanoic acid was solubilized in alpha-cyclodextrin solution, and the 2- hydroxylated product was quantified by gas chromatography-mass spectrometry after conversion to a trimethylsilyl ether derivative. When the microsomes of FA2H-transfected COS7 cells were incubated with the electron transfer system and deuterated tetracosanoic acid, deuterated 2- hydroxy tetracosanoic acid was formed in a time- and protein- dependent manner. With this method, FA2H activities were reproducibly measured in murine brains and tissue culture cell lines. Alderson, N.L.,M. D. Walla, and H. Hama. A novel method for the measurement of in vitro fatty acid 2-hydroxylase activity by gas chromatography-mass spectrometry.