Phospholipase molecular weight

Capacitative Ca2+ entry is the predominant mode of regulated Ca2+ entry in nonexcitable cells but it also occurs in a number of excitable cell types. This pathway of Ca2+ entry is usually associated with the activation of phospholipase C, which mediates the formation of IP3 (see Ch. 20). Intracellular application of IP3 mimics the ability of hormones and neurotransmitters to activate calcium ion entry, and activation of calcium ion entry by hormones and neurotransmitters can be blocked by intracellular application of low-molecular-weight heparin, which potently antagonizes IP3 binding to its receptor. There is considerable evidence for the presence of an IP3 receptor in the plasma membrane of some cells types. 1(1,3,4,5)P4, a product of IP3 phosphorylation, has been shown in some cells to augment this action of IP3 in activating PM calcium ion entry, but in others IP3 alone is clearly sufficient. 

Synaptic stimulation, ischemia or seizure activates phospholipase A2 and releases arachidonic and docosahexaenoic acids 578 Secretory phospholipases A2 are of relatively low molecular weight and have a high number of disulfide bridges, making them relatively more resistant to denaturation 579 There are high-affinity receptors that bind secretory phospholipase A2 579... 

Almost all receptor-mediated neutrophil functions are mediated via GTP-binding proteins (G-proteins), which provide the link between occupancy of plasma membrane receptors and the activation of intracellular enzymes, such as phospholipases and protein kinases. There are two groups of G-proteins those that are heterotrimeric and those with low molecular weight. 

Phospholipase C from B. cereus contains two zinc ions per molecule of protein (molecular weight 23 000), the two metal ions being about 5 A apart. The zinc appears to have a particular role in the stabilization of the protein structure.585 Added Zn11 protects the enzyme against denaturation and induces the refolding of the denatured enzyme. Other metals are much less effective than zinc in carrying out this function.586... 

J Chen, SJ Engle, JJ Seilhamer, JA Tischfield. Cloning and recombinant expression of a novel human low molecular weight Ca(2+)-dependent phospholipase A2. J Biol Chem 269 2365-2368, 1994. 

Gassama-Diagne, A., Fauvel, J., and Chap, H. (1989) Purification of anew, calcium-independent, high molecular weight phospholipase A2/lysophospholipase (phospholipase B) from guinea pig intestinal brush-border membrane, J. Biol. Chem. 264, 9470-9475. 

Figure 4. Linear representation of the Arabidopsis PIPKs and PLCs. The Arabidopsis PtdlnsP 5-kinases are most similar to the human type I PtdlnsP 5-kinases. There are 11 putative type I /I/PtdlnsP 5-kinases in Arabidopsis arranged in two subfamilies based on size. Subfamily B contains X/PIPK1-9, all of which contain membrane occupation and recognition nexus (MORN) repeats. /1/PIPK10-11 are in Subfamily A with molecular weights less than that of the members of subfamily B and contain no MORN repeats. The Arabidopsis phosphoinositide specific phospholipase C family is most similar to the animal PLC . There are seven functional PI-PLCs in Arabidopisis (Hunt et al., 2004). All isoforms contain EF-hand motifs, the X and Y catalytic domains characteristic of PI-PLCs and a C2 lipid-binding domain.

Our knowledge of porcine pancreatic phospholipase comes from the laboratory of G. H. de Haas and his co-workers. The enzyme is quite different from pancreatic lipase (Table VIII). Its molecular weight is quite small, it is a metalloenzyme that requires Ca ion as a cofactor, and it is excreted from the pancreas as a proenzyme which is then activated by trypsin with removal of a heptapeptide. The molecule has six... 

Stahl, U., M. Lee, S. Sjodahl, D. Archer, F. Cellini, B. Ek, R. lannacone, D. Mackenzie, L. Semeraro, and E. Tramontane. 1999. Plant low-molecular-weight phospholipase A2s (PLA2s) are structurally related to the animal secretory PLA2s and are present as a family of isoforms in rice (Oryza sativa). Plant Mol. Biol. 41 481 90. 

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