Assay and Purification of Plasmalogen-Selective Phospholipase A2 and Lysoplasmalogenase Activities
Plasmalogens represent a special group of glycerophospholipids characterized by a vinyl ether bond at the sn-1 position and arachidonic acid or docosahexaenoic acid at the sn-2 position, and the sn-3 carbon usually has a phospholipid head group like choline or ethanolamine at the glycerol backbone. In all mammalian cells, these glycerophospholipids are especially rich in brain, heart, and red blood cells. While choline plasmalogen is rich in heart, ethanolamine plasmalogen is rich in brain white matter. On the basis of various studies, it is suggested that ethanolamine plasmalogens are abundant in cholesterol-rich biomembranes having long life spans, such as nervous system myelin and red blood cells (Farooqui and Horrocks, 2004). Although the role of plasmalogens is not fully understood, collective evidence suggests that besides being structural component and reservoir for arachidonic and docosahexaenoic acids in neural membranes, plasmalogens play an important role in signal transduction processes, membrane dynamics, membrane fusion, and protection against oxidative stress (Farooqui and Horrocks, 2001). On the basis of two-dimensional NMR studies, it is proposed that choline and ethanolamine plasmalogens have a different glycerol backbone conformation with respect to the membrane interface than diacylglycerophospholipids (Han and Gross, 1990). This unique conformation motif is selectively recognized by enzymes responsible for receptor-mediated breakdown of plasmalogen (Farooqui et al., 2003). The stimulation of kainate type of glutamate receptors on neuronal cell surface results in the stimulation of the Ca2+-independent plasmalogen-selective PLA2 (PlsCho-PLA2 and PlsEtn-PLA2) and generation of arachidonic or docosahexaenoic acids and lysoplasmalogen (Farooqui et al., 2003). Arachidonic and docosahexaenoic acids are metabolized to eicosanoids and docosanoids, respectively. Lysoplasmalogen is either reacylated to plasmalogen or hydrolyzed by lysoplasmalogenase (Farooqui et al., 2003; Farooqui and Horrocks, 2007). Plasmalogen-selective-PLA2 has been purified and characterized from various sources including heart, brain, and kidney (Hazen and Gross, 1993; Hirashima et al., 1992; Portilla and Dai, 1996). The activity of this enzyme can be determined by radiochemical and fluorometric procedures (Farooqui and Horrocks, 1988).
KeywordsAlcohol Dehydrogenase Docosahexaenoic Acid Fatty Aldehyde Free Aldehyde Brain Microsome
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