Phospholipase physiological role

Pappan, K., and Wang, X., 1999, Molecular and biochemical properties and physiological roles of plant phospholipase D. Biochim. Biophys. Acta 1439 151-166. 

Mukherjee AB, Miele L, Pattabiraman N. Phospholipase A2 enzymes - regulation and physiological-role. Biochem Pharmacol 1994 48 1-10. 

Histamine released from mast cells plays an important physiological role in immediate hypersensitivity and allergic responses. In addition, histamine functions as a neurotransmitter in the CNS and it is a potent stimulus for gastric acid secretion. These actions depend on the interaction of histamine with two types of receptors, Hi and H2. Hi and H2 receptors are coupled via G proteins to phospholipase C and adenylyl cyclase, respectively. The principal H3 receptor response is stimulation of gastric acid secretion, whereas other actions of histamine (e.g., smooth muscle contraction, vasodilation, increased capillary permeability, pain, and itching) are prunarily mediated by Hi receptors. 

Phospholipase Aq Structures, Physiological and Patho-physiological Roles in Mammals... 

Sapirstein A, Bonventre JV. 2000. Specific physiological roles of cytosolic phospholipase A(2) as defined by gene knockouts. Biochim Biophys Acta 1488 139-148. 

Hirabayashi T., Murayama T., Shimizu T. Regulatory mechanism and physiological role of cytosolic phospholipase A2. Biol. Pharm. Bull. 27 (2004) 1168-1173. 

In a provocative paper entitled, Is Phospholipase D ReaUy an Enzyme , Roughan and Slack (1976) have concluded that phospholipase D may not have a physiological role but that it is a structural protein which, under certain nonphysiological conditions, possesses enzymatic activity. Their conclusions were based on results obtained by comparing in situ reactions with in vitro properties of the enzyme. Needless to say, further investigation is required to resolve these problems. 

As shown in Table 1, lAP-substrate G-proteins having a-subunits of Mr=40,000 have been purified from rat brain (tentatively referred to as Go in Table 1 (32) and from HL-60 cells that had been differentiated to neutrophils by dimethylsulfoxide [referred to as Ghl (33)]. They differ from G-proteins previously purified, since neither of them interact with any of the antibodies currently available for the G-proteins, i.e., those raised against purified a-subunits of Gi and Go and purified py. It remains to be determined whether these new lAP substrates with apparently identical molecular weights are really identical with each other. Nor is any decisive information available for the physiological role of Go, Go and Ghl, although the latter one is a candidate of the G-protein acting as transducer between the chemotactic peptide receptors and phospholipase C in neutrophils. This is because activation of the phospholipase by the chemotactic peptide in neutrophils was abolished by prior treatment of the cells with lAP (20-22, 34). A similar lAP-substrate G-protein has been partially purified firom sea urchin eggs (35). 

Preliminary results obtained with whole or sonicated vacuoles suggested that phospholipase Ai is located on the cytoplasmic face of the vacuolar membrane. Further investigations about acyl chain-specificity of tonoplast phospholipase A, its location within the membrane and its mode of regulation will be necessary to clarify its physiological role. 

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