Diacyl kinase

If positions 1 and 2 are acylated and the sn-3 hydroxyl group is free, the lipid is l,2-diacyl-s -glycerol (DAG). The DAGs play both a biosynthetic (see later) and a cellular regulating role in that they activate protein kinase C (PKC) (see Chs 20 and 23). In addition, DAGs can be... 

There are several subfamilies of PKs, which either require Ca2+, diacyl glycerol or phorbol esters or extracellular agonists for activation. Four major groups of PKs are distinguished. Basic amino acid-directed kinases (PKA, PKB, PKC) phophorylate serine/threonine around such amino acid residues. PKA is activat-... 

The role of protein kinase C in many neutrophil functions is undisputed and has been recognised for some time. For many years it was believed that the source of DAG, the activator of protein kinase C, was derived from the activity of PLC on membrane phosphatidylinositol lipids. Whilst this enzyme undoubtedly does generate some DAG (which may then activate protein kinase C), there are many reasons to indicate that this enzyme activity is insufficient to account for all the DAG generated by activated neutrophils. More recently, experimental evidence has been provided to show that a third phospholipase (PLD) is involved in neutrophil activation, and that this enzyme is probably responsible for the majority of DAG that is formed during cell stimulation. The most important substrate for PLD is phosphatidylcholine, the major phospholipid found in neutrophil plasma membranes, which accounts for over 40% of the phospholipid pool. The sn-1 position of phosphatidylcholine is either acyl linked or alkyl linked, whereas the sn-2 position is invariably acyl linked. In neutrophils, alkyl-phosphatidylcholine (1-0-alky 1-PC) represents about 40% of the phosphatidylcholine pool (and is also the substrate utilised for PAF formation), whereas the remainder is diacyl-phosphatidylcholine. Both of these types of phosphatidylcholine are substrates for PLD and PLA2. 

This enzyme [EC 2.7.1.107], also known as diglyceride kinase, catalyzes the reaction of ATP with a 1,2-diacyl-... 

Inogudii T, Battan R, Handler E, Sportsman JR, Heath W, King GL (1992) Preferential elevation of protein kinase C isoform pll and diacyl ycerol levels in the aorta and heart of diabetic rats differential reversibility to ycemic control by islet cell transplantation. Proc Natl Acad Sd USA 89 11059-11063... 

Furthermore, the LPS signal transduction involves the activation of G proteins, of phospholipases C and D, the formation of diacyl-glycerol (DG) and inositol triphosphate (IP3). DG mediates the stimulation of protein kinase C (PKC) and IP3 induces an increase of cytosolic Ca++ The LPS signaling pathway also involves tyrosine kinases, constitutive nitric oxide (NO) synthase (cNOS), cGMP-dependent protein kinase, Ca channels, calmodulin and calmodulin kinase [27,28], as well as the MAP kinases [29] ERK1, ERK2 and p38 [23], The intracellular events in response to LPS are due to lipid A because they are inhibited by polymyxin B which is known to bind lipid A [27] and they are reproduced by lipids A [30,31]. 

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). 

DAGK (diacyl glycerol kinase)94 Nanocrystals 0.3 ppm 15N (deconvolution of Leu spectrumc) 268 K Protein retained native lipids... 

Ca + is required for phosphorylase activation in fat bodies of both P, americana (25) and discoidalis (personal observation). Addition of Ca + elevates fat body phosphorylase kinase activity in P. americana (33). and calmodulin inhibitors suppress CC-stimulated trehalose production by the fat body in vitro. However, direct addition of calmodulin to fat body phosphorylase kinase also suppresses the kinase activity. It is proposed that Ca + interacts directly with a calmodulin-like subunit of phosphorylase kinase to activate the enzyme, and the presence of exogenous calmodulin competes with the enzymic subunit for available Ca + (33). These results suggest that the HGHs may influence adipocyte Ca + levels related to phosphorylase activation to promote glycogenolysis for trehalose synthesis. Possibly, HGH-mediated fat body Ca levels may interact with polyphosphoinositides, diacyl glycerol and protein kinase C as second messengers for endocrine message transduction and phosphorylase activation. 

Figure 9.7 Effects of cAMP contributing to relaxation. AC, adenylate cyclase DG, diacyl glycerol G, guanosine nucleotide regulatory protein IP3, Inositol trisphosphate, MLCK, myosin light chain kinase.

Activation of receptor tyrosine kinases leads to stimulation of phospholipid metabolism and to the generation of multiple second messengers. Phospholipase Cy binds through its SH2 domain to phosphotyrosine sites on the receptor molecules and is thereby activated. As a consequence of phospholipase Cy activation, Ca2+ and diacyl-glycerol signals are produced leading, e. g., to the activation of protein kinase C isoenzymes and of CaM kinases. 

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)... 

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