Turnover Rates of the Molecular Species of Ethanolamine Plasmalogen of Rat Brain

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Abstract
1,2‐Diradyl‐3‐acetylglycerols prepared from 1‐O‐alk‐l'‐enyl‐2‐acylglycero‐3‐phosphoethanolamine (alkenylacyl‐GPE, ethanolamine plasmalogen) and 1‐alkyl‐2‐acylglycero‐3‐phosphoethanolamine (alkylacyl‐GPE) of rat brain at 18 days of age were subfractionated into six species by AgNO3impregnated TLC. The percent compositions of subfractions were compared with that of 1,2‐diacylglycero‐3‐phosphoethanolamine (diacyl‐GPE). The incorporation rate of [1‐3H]glycerol into each molecular species was also estimated to examine the turnover rate and selective synthesis of molecular species of ethanolamine phosphoglycerides (EPG). Among the molecular species of EPG, a major proportion contained polyun‐saturated fatty chains, and the sum of tetraene‐, pentaene‐, and hexaene‐containing species was >65% in common with three classes of EPG. It was possible to calculate the turnover time, synthesis rate, and synthesis rate constant of ethanolamine plasmalogen in myelinating rat brain by the equation of Zilversmit et al. since the time‐dependent change of specific activity and the distribution of molecular species indicated that each molecular species of alkenylacyl‐GPE is synthesized from the corresponding species of alkylacyl‐GPE. The observed turnover lime of ethanolamine plasmalogen was about 5 h. The observed turnover times of the various molecular species were of the order: tetraene hexaene > pentaene monoene diene. The synthesis rate constants of each molecular species, in the formation of alkenylacyl‐GPE from alkylacyl‐GPE, were of the order: hexaene > tetraene > pentaene > diene monoene. This result indicated that the hexaene species is preferentially synthesized from alkylacyl‐GPE among molecular species of ethanoiamine plasmalogen in the desaturation of alkylacyl‐GPE.

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