Phospholipase phosphodiesterase activity

Therefore, it is currently believed that anandamide is formed from membrane phospholipids (Fig. 4) through a pathway that involves (1) a trans-acylation of the amino group of phosphatidylethanolamine with arachidonate from the sn-1 position of phosphatidylcholine and (2) a D-type phosphodiesterase activity on the resulting A-arachidonylphosphati-dylethanolamide (NAPE). Synthesis of anandamide is presumably regulated at the levels of both enzymes, the A-acyltranferase and the phospholipase D, by stimuli that raise intracellular calcium or by receptors linked with cAMP and PKA. It has been shown that anandamide is formed when neurons are depolarized and, therefore, the intracellular calcium ion levels are elevated (Cadas, 1996). 

Another important group of hydrolytic enzymes are phospho- and cyclophosphodiesterases. They catalyze the hydrolysis of phospho-diester bonds and many of the most relevant biological substrates are nucleic acids. Phospholipase C and D are also important examples. Initial attempts to measure phosphodiesterase activity placed a phosphodiester between a fluorophore and a quencher and the probe was tested in vitro [146], This system was slightly modified by Caturla and used for the identification of catalysts with phosphodiesterase activity [147], More recently, Nagano and co-workers used a coumarin donor and fluorescein as a FRET... 

Phosphodiesterase (Hydrolysis) Activity. A rather broad substrate specificity is exhibited by the purified phospholipase D (phosphodiesterase activity). It can attack phosphatidylcholine, phosphatidylethanolamine, phospha-tidylserine, and phosphatidylglycerol. In most cases, Ca2+ was an activator, but variable results were obtained on the positive influence of diethyl ether on the catalytic activity of different sources of this enzyme. Usually the optimum pH was in the range from 5.0 to 7.0. Mammalian phospholipase D, containing both the phosphodiesterase and transphosphatidylase activities, exhibited a broad-range substrate specificity similar to that of the plant enzyme. However, the mammalian enzyme showed a dependency for the presence of oleic acid in the reaction system (Kobayashi and Kanfer, 1991). 

Volwerk, J.J., Shashidhar, M.S., Kuppe, A., and Griffith, O.H., 1990, Phosphatidylinositol-specific phospholipase C from Bacillus cereus combines intrinsic phosphotransferase and cyclic phosphodiesterase activities A 31P NMR study. Biochemistry 29 8056-8062. 

Burstein and Hunter (1995) observed that THC stimulated the biosynthesis of anandamide in neuroblastoma cells employing either ethanolamine or arachidonic acid as the label. Anandamide bios5mthesis has also been shown to occur in primary cultures of rat brain neurons labelled with [H]-ethanolamine when stimulated with ionomycin, a Ca ionophore (Di Marzo et al. 1994). These authors proposed an alternate model for the biosynthesis of anandamide in which N-arachidonoyl phosphatidyl ethanolamine is cleaved by a phospholipase D activity to yield phosphatidic acid and ararchidonoylethanolamide. This model is based upon extensive studies undertaken by Schmid and collaborators (1990), who have shown that fatty acid ethanolamide formation results from the N-acylation of phosphatidyl ethanolamine by a transacylase to form N-acyl phosphatidylethanolamine. Possibly resulting from postmortem changes, this compound is subsequently hydrolyzed to the fatty acid ethanolamide and the corresponding phosphatide by a phosphodiesterase, phospholipase D. 

Muller, G., Grey, S., Jung, C., and Bandlow, W. Insulin-like signaling in yeast modulation of protein phosphatase 2A, protein kinase A, cAMP-specific phosphodiesterase, and glycosyl-phospha-tidylinositol-specific phospholipase C activities. Biochemistry, 2000, 39, 1475-1488. 

The family of heterotrimeric G proteins is involved in transmembrane signaling in the nervous system, with certain exceptions. The exceptions are instances of synaptic transmission mediated via receptors that contain intrinsic enzymatic activity, such as tyrosine kinase or guanylyl cyclase, or via receptors that form ion channels (see Ch. 10). Heterotrimeric G proteins were first identified, named and characterized by Alfred Gilman, Martin Rodbell and others close to 20 years ago. They consist of three distinct subunits, a, (3 and y. These proteins couple the activation of diverse types of plasmalemma receptor to a variety of intracellular processes. In fact, most types of neurotransmitter and peptide hormone receptor, as well as many cytokine and chemokine receptors, fall into a superfamily of structurally related molecules, termed G-protein-coupled receptors. These receptors are named for the role of G proteins in mediating the varied biological effects of the receptors (see Ch. 10). Consequently, numerous effector proteins are influenced by these heterotrimeric G proteins ion channels adenylyl cyclase phosphodiesterase (PDE) phosphoinositide-specific phospholipase C (PI-PLC), which catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) and phospholipase A2 (PLA2), which catalyzes the hydrolysis of membrane phospholipids to yield arachidonic acid. In addition, these G proteins have been implicated in... 

Dopamine activates adenylate cyclase and phospholipase C (PLC) via a D, receptor and inhibits through a D2 receptor, thereby regulating the production of intracellular second messengers, cAMP, Ca2+, and 1,2-diacylglycerol. D, and D2 receptors are decreased in the striatum of patients with dementia. There is considerable evidence to suggest that intracellular levels of cAMP have a protective role for dopaminergic neurons. Intracellular concentrations of cyclic nucleotides are regulated by cyclic nucleotide phosphodiesterases and CaMPDE, one of the most intensely studied and best-characterized phosphodiesterases. 

The Ca2+-phosphoinositide signaling pathway. Key proteins include hormone receptors (R), a G protein (G), a phosphoinositide-specific phospholipase C (PLC), protein kinase C substrates of the kinase (S), calmodulin (CaM), and calmodulin-binding enzymes (E), including kinases, phosphodiesterases, etc. (PIP2, phosphatidylinositol-4,5-bisphosphate DAG, diacylglycerol. Asterisk denotes activated state. Open arrows denote regulatory effects.)... 

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