Synthesis of PS and formation of PE in the mitochondrial PSDecarboxylation pathway

[[Phosphatidylserine|Phosphatidylserine (PS)]] is formed by the condensation of serine with a [[Phosphatidic acid|phosphatidic acid (PA)]] moiety, where in mammalian cells [[Glycerophosphocholines (GP01)|phosphatidylcholine (PC)]] or [[Glycerophosphoserines (GP03)|phosphatidyl ethanolamine (PE)]] serve as the phosphatidyl donors catalyzed by PS-Synthases (PSS I/II) (Fig. 25 below). Nascent [[Phosphatidylserine|PS]] is subsequently decarboxylated to form [[Glycerophosphoserines (GP03)|PE]], and this reaction is catalyzed by PS-Decarboxylase (PSD) (Fig. 25 below). Both the [[Phosphatidylserine|PS]] and [[The “Kennedy pathway” as the majour route of PC and PE synthesis|“Kennedy pathway”]] are found in mammalian cells but there are some tight restrictions on specific elements of the pathways. In contrast to yeast, the methylation reaction in mammalian cells is not sufficient for supplying all of the [[Glycerophosphocholines (GP01)|PC]] needed for cell growth. The methylation of [[Glycerophosphoserines (GP03)|PE]] only occurs quantitatively significant in the liver. <br> [[Image:Figure 25 Synthesis and catabolism of phosphatidylserine to phosphatidyethanolamine.jpg|Figure 25.Synthesis and catabolism of phosphatidylserine to phosphatidyethanolamine]] <br> In the last years the [http://en.wikipedia.org/wiki/Endoplasmic_reticulum endoplasmic reticulum] and a novel ER-related fraction have been identified as the principal intracellular localization sites of PS-Synthase. The ER-related fraction is tightly associated with the [http://en.wikipedia.org/wiki/Mitochondria mitochondria] and currently referred to as the mitochondria-associated membrane (MAM) compartment (Fig. 26 below). The MAMcompartment can be isolated as a distinct cellular fraction and has significant enrichment in PS-Synthase activity when compared with the total microsomal membrane population. Both morphological and biochemical studies have suggested that the zones of association between the MAM and the mitochondria may also be sites of contact between the outer and inner mitochondrial membrane (Fig. 26).<br> [[Image:Figure 26 ER and MAM compartment associated PS-metabolism.jpg|Figure 26. ER and MAM compartment associated PS-metabolism]] <br> PS-Decarboxylase was found to be a constituent of the inner mitochondrial membrane and there is a preference for the movement of newly synthesized [[Phosphatidylserine|PS]] to [http://en.wikipedia.org/wiki/Mitochondria mitochondria]. The [[Glycerophosphoserines (GP03)|PE]] generated in [http://en.wikipedia.org/wiki/Mitochondria mitochondria] does not only serve as a structural lipid in the [http://en.wikipedia.org/wiki/Mitochondria mitochondria] but is preferentially utilized as a substrate for the methyltransferase reaction to form [[Glycerophosphocholines (GP01)|PC]] and additionally is exported from mitochondria to function in the biogenesis of other organelles. The mechanism by which mitochondrial [[Glycerophosphoserines (GP03)|PE]] is transported to the plasma membrane is not known, but the process is energy dependent and insensitive to the [http://en.wikipedia.org/wiki/Golgi_apparatus Golgi] disrupting toxin brefeldin A. The results with brefeldin A indicate that the route followed by [[Glycerophosphoserines (GP03)|PE]] is likely to bypass the [http://en.wikipedia.org/wiki/Golgi_apparatus Golgi apparatus]. <br> Other pages in this category: <br> &lt;categorytree mode=all hideroot=on&gt;Phospholipid_metabolism&lt;/categorytree&gt; <br> <br>