Diacyl phosphorylation

The different phosphoglycerides are often named by placing the constituent attached to the phosphate group after phosphatidyl , e.g. phosphatidyl choline (3-in-phosphatidylcholine or l,2-diacyl-sn-glycero-3-phosphoryl-choline). There are many phosphoglycerides because of the possible variation in the fatty acid chains, and when the full chemical structure is known, it should be used (e.g. l-palmitoyl-2-oleoyl-phosphatidylcholine). Nomenclature that entails the use of the DL system should be avoided. 

The first steps of glycerophospholipid synthesis are shared with the pathway to triacylglycerols (Fig. 21-17) two fatty acyl groups are esterified to C-l and C-2 of L-glycerol 3-phosphate to form phosphatidic acid. Commonly but not invariably, the fatty acid at C-l is saturated and that at C-2 is unsaturated. A second route to phosphatidic acid is the phosphorylation of a diacyl-glycerol by a specific kinase. 

After activation of the TCR, there is induction of Src family tyrosine kinase (p56lek), which phosphorylates phospholipase Oyl. This is followed by the hydrolysis of phosphatidylinositol 4,5-bisphosphate, resulting in the production of diacyl-glycerol (DAG) and inositol trisphosphate (IP3). Protein kinase C is activated by DAG, which phosphorylates Ras. Ras is a GTPase and its phosphorylation induces Raf and initiation of MAP kinase signaling pathway. IP3 is involved in calcium-dependent activation of IL-2 gene expression via nuclear factor of activated T cells (NFAT). 

With the exception of an isolated reports on the decomposition of diacyl peroxides in acetonitrile in the presence of copper(II) isothiocyanate and potassium dtiocyanate (equation 32), the only preparative methods available for decarboxylative chalcogenation and phosphorylation make use of the 0-acyl duo-hydroxamates. 

Compounds of this type include some of the imidazolinones or imidazolinethiones which can be in equilibrium with the fully aromatic hydroxy or thiol forms (Section 4.06.5.1). The non-aromatic forms may be quite stable in some instances, but may also react in the aromatic form. Thus, 5//-imidazolin-4-ones (170) are acylated under Schotten-Baumann conditions on the exocyclic oxygen. When the reaction conditions are altered it is possible to obtain products of JV-acylation and A(,0-diacylation (71CHE746). With the same compound a Mannich reaction takes place at the 5-position, and phosphoryl chloride gives products of O- and (V-phosphorylation rather than nucleophilic chlorination (Scheme 81). 

The formation of diacyl glycerol implies the participation of phospholipase C. A simple pathway would entail receptor activation by cross-phosphorylation, followed by the binding of phospholipase C y (through its SH2 domains). The participation of phospholipase C indicates that IP would be formed and, hence, calcium concentrations would increase. 

Before we leave our brief survey of intracellular Ca -binding proteins, we must write a few lines about an important Ca " -regulated kinase (a phospho-rylating enzyme), i.e., protein kinase C (PKC). The activity of this enzyme, or rather family of enzymes,appears to be regulated by three factors phospholipids, in particular phosphatidylserine diacyl-glycerols, one of the products of inositol lipid breakdown and Ca " ions. The high-activity form of PKC, which appears responsible for much of the phosphorylation activity of many cells, is presumably membrane-bound, whereas the low-activity form may be partly cytosolic (Figure 3.27). The schematic structure of rabbit PKC (Mr 11 kDa)... 

Phosphatidylcholines (PC), (l,2-diacyl-s -glycerol-3-phosphoryl-cholinc) are predominant in animal cell membranes [7]. They are often called lecithins (Greek name "lekilhos the egg yolk) and their content in the biomembranes or animal tissues is very high. They are the main lipid compounds of plant membranes but their proportion in bacterial... 

Plasmalogens are a group of phosphoglycerides which are phosphorylated derivatives of 1-alk-cw-l-enyl-2-acyl-5n-glyceroL The similarity in properties between plasmalogens and the corresponding 1,2-diacyl phospholipids has made isolation procedures difficult. Moreover, chemical synthesis is made... 

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