title: Substrate preference in phosphatidylserine biosynthesis for docosahexaenoic acid containing species.
abstract: Neuronal membranes contain high levels of phosphatidylserine (PS) and docosahexaenoic acid (22:6n-3, DHA). In this study, substrate preference in PS synthesis was determined to gain insight on the biochemical basis for concentrating PS in neuronal membranes where 22:6n-3 is highly enriched. We first established an in vitro assay method using unilamellar vesicles (LUV) of deuterium-labeled substrates and reversed-phase HPLC/electrospray ionization (ESI) mass spectrometry. The PS production by the incubation of deuterium-labeled substrate and microsomal fractions was monitored. We found that tissue-specific substrate preference exists in PS synthesis. Microsomes from the cerebral cortex synthesized PS from 18:0,22:6-PC most favorably among the PC substrates tested, followed by 18:0,22:5-PC, resulting in the PC substrate preference in the order of 18:0,22:6 > 18:0,22:5 > 18:0,20:4 = 18:0,18:1. Liver microsomes also preferred 18:0,22:6-PC as the substrate in PS synthesis but did not use 18:0,22:5-PC favorably. The 18:0,22:5-PC species was converted to PS at the similar extent as 18:0,20:4- or 18:0,18:1-PC species in the liver. Both brain and liver microsomes showed a preference for 18:0 over 16:0 as the sn-1 fatty acid. From these data it was deduced that preferential conversion of 18:0,22:6-PC to the corresponding PS species is at least partly responsible for concentrating PS in neuronal tissues where 22:6n-3 is particularly abundant. The distinctive preference for 18:0,22:5-PS observed with brain microsomes may help to maintain PS at a high level in the brain when 22:6n-3 is replaced by 22:5n-3 as in the case of n-3 fatty acid deficiency.
authors.affiliation: Section of Mass Spectrometry, Laboratory of Membrane Biochemistry and Biophysics, NIAAA, National Institutes of Health, Rockville, Maryland 20852, USA. hykim@nih.gov
authors.forename: Hee-Yong
authors.initials: HY
authors.lastname: Kim
authors.forename: James
authors.initials: J
authors.lastname: Bigelow
authors.forename: Jillonne H
authors.initials: JH
authors.lastname: Kevala
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003903:Deuterium / Q000737:chemistry; D004281:Docosahexaenoic Acids / Q000737:chemistry* / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry; D008861:Microsomes / Q000737:chemistry / Q000378:metabolism*; D008862:Microsomes, Liver / Q000737:chemistry / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry; D010718:Phosphatidylserines / Q000096:biosynthesis*; D051381:Rats; D012694:Serine / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013379:Substrate Specificity
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D004281:Docosahexaenoic Acids; D012694:Serine; D003903:Deuterium