Phospholipase occurrence

Song JK, Han JJ, Rhee IS. 2005. Phospholipases Occurrence and production in microorganisms, assay for high throughput screening, and gene discovery from natural and manmade diversity. J Am Oil Chem Soc 82 691-705. 

Phosphohpases of type Cy are activated by receptor tyrosine kinases (see Chapter 8), and thus phosphohpase Cy is involved in growth factor controlled signal transduction pathways. The receptor tyrosine kinases (see Chapter 8) phosphorylate the enzyme at specific tyrosine residues and initiate activation of the enzyme. Characteristic for the structure of phospholipase Cy is the occurrence of SH2 and SH3 domains (see Chapter 8). These represent protein modules that serve to attach further partner proteins. 

Although the occurrence of analogs of PAF in mammalian cells was always considered a possibility, Mueller et al. (1984) first reported the presence of 1-0 long-chain acyl-2-acetyl-glycero-3-phosphocholine in rabbit neutrophils. Later, Tokumura et al. (1989) isolated a vasopressor active phosphatidylcholine fraction from bovine brain. Treatment of the fraction with phospholipase C yielded a diglyceride component which was converted to the t-butyldimethylsilyl derivative. Analysis of the latter by gas-liquid chroma-... 

Figure 20.8 is a view from the reaction cell window under the optimum condition to obtain the LPC. As can be seen, phospholipase Aj stuck on the wall of the reaction cell and window. Under ordinary conditions for enzymatic reaction, both in aqueous and in nonaqueous media, occurrence of the adhered enzyme should seriously impair the efficiency of the enzymatic reaction. However, in... 

The subsequent signaling events downstream of chemokine-mediated G-protein activation are complicated. It has already been mentioned that signaling events from chemokine receptors are commonly inhibited by pertussis toxin, leading to the assumption that chemokine receptors are Ga linked. One of the most rapid occurrences following chemokine receptor activation is a rise in the intracellular calcium concentration dCa +]i), and this has commonly been used as a measurement for the functional response of receptor activation. Increases in [Ca " "] are mediated via the jSy subunit of the G-protein that activates phospholipase CjS, leading to 1) hydrolysis of phosphatidylinositol to IP3 and 2) DAG formation, which respectively induce the release of Ca + from intracellular stores and subsequent activation of PKC. PKC activation is necessary for certain leukocyte responses, such as neutrophil respiratory burst (Li et al., 2000), and it also plays a role in receptor phosphorylation, leading to desensitization and internalization, which will be discussed later. 

The production of free inositol from phosphatidylinositol suggests the possibility that a phospholipase D type of activity might be involved in this system. The occurrence of phospholipase D in animal tissues was not reported until recently, when an enzyme which cleaves phosphatidylcholine to give choline and phosphatidic acid was found in brain tissue (Saito Kanfer, 1975). It is not known whether phosphatidylinositol can act as its substrate in an analogous reaction. 

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