Phospholipid turnover

Phospholipid turnover also takes place in an asymmetric manner. The enzymes responsible for phospholipid turnover in response to receptor-mediated phospholipase c activation are active from the cytoplasmic surface of the membrane. Likewise, diacylglycerol kinases converting the product of phospholipase c back into the key intermediate of phospholipid biosynthesis, phosphatidic acid, are also located on the cytoplasmic smface of the membrane (Sanjuan et al., 2001). 

While ionophore-stimulated 5-LO product release from neutrophils is often used as an indication of 5-LO inhibition, one must interpret these results cautiously. For example, halothane, an inhalation anaesthetic which may cause membrane perturbation [26], and colchicine, a microtubule disrupter [27], both were active, but presumably not because of 5-LO inhibition. A23187 is assumed to stimulate 5-LO by raising the intracellular calcium level, but this agent causes many other effects which may or may not be related to 5-LO activation, including changes in membrane potential, protein phosphorylation, phospholipid turnover, cyclic nucleotide levels, and DNA and protein synthesis [28]. Also, the effects of some putative 5-LO inhibitors on product release from neutrophils has been shown to vary with the stimulant used [29]. 

Takai, Y, Kishimoto, a., and Nishizuka, Y. (1982). Calcium and phospholipid turnover as transmembrane signaling for protein phosph(xylation, pages 386 in Calcium and Cell Function, Vol. II, Cheung, W.Y., Ed. (Academic Press, New York). 

Esterases Group of enzymes involved in phospholipid turnover in cell membranes. Esterase activity in algae has been shown to relate well to metabolic activity and cell viability. Volume 1 (5). 

Receptors for protein hormones can be coupled to different transducing systems. Most of the data from studies approximately 10 years ago showed that many receptors are coupled to the adenylate cyclase system. However in the early 1980s it became clear that calcium fluxes and phospholipid turnover could also be important in conveying hormonal signals. During the last few years the number of papers describing the effects of hormones on phospholipid metabolism and calcium fluxes has increased tremendously and has outnumbered studies on cyclic AMP. 

Morse, M.J., Crain, R.C., and Satter, R.L., 1987, Light-stimulated inositol phospholipid turnover in Samanea saman leaf pulvini. Proc. Natl. Acad. Sci. U.S.A. 84 7075-7078. 

Kamada, Y. and Muto, S., 1994, Stimulation by fungal elicitor of inositol phospholipid turnover in tobacco suspension culture cells. Plant Cell Physiol. 35 397—404. 

Drory, A., Borochov, A., and Mayak, S., 1992, Transient water stress and phospholipid turnover in carnation flowers. J. Plant Physiol. 140 116-120. 

Chock, S. P., Rhee,S. G.,Tang, L. C., andSchmauder-Chock, A. (1991). Linking phospholipase A2 to phospholipid turnover and prostaglandin synthesis in mast cell granules. Eur.J. Biochem. 195, 707-713. 

Kanterman RY, Felder CC, Brenneman DE, Ma AL, Fitzgerald S, Axelrod J. arAdrenergic receptor mediates arachidonic-acid release in spinal-cord neurons independent of inositol phospholipid turnover. J Neurochem 1990 54 1225-1232. 

Puri BK, Richardson AJ, Horrobin DF, Easton T, Saeed N, Oatridge A, etal. Eicosapentaenoic acid treatment in schizophrenia associated with symptom remission, normalisation of blood fatty acids, reduced neuronal membrane phospholipid turnover and structural brain changes. Int J Clin Prac 2000 54( 1 ) 57—63. 

Epinephrine stimulated glucose oxidation while inhibiting P uptake into phospholipids in incubating dog thyroid slices (A8). Recently Pastan (P3) reported that fluoride, which stimulates the formation of cyclic AMP, increased the rate of glucose oxidation and phospholipid turnover in thyroid slices. However, it did not increase colloid droplet formation in the follicles. Colloid droplet formation is a characteristic action of TSH (D2). Although TSH may indeed stimulate the hexose monophosphate shunt, its specificity must involve other pathways as well. 

Investigation of phospholipid catabolic and anabolic enzymes revealed lower activity of PLA2 and phosphoethanolamine- and phosphocholine-cytidylyltransferases in autopsied substantia nigra of patients with idiopathic Parkinson s disease. The decreased rate of phospholipid turnover in the pigmented neurons of the substantia nigra might result in reduced ability to repair oxidative membrane damage and thus accumulation of OxPL in Parkinson s disease (Ross et al. 2001). 

Fig. 9. Phospholipid turnover. The 1,2-diacylglyceroI kinase cycle involves the (1) transfer of the sn-1 -glycerol phosphate moiety from phosphatidylglycerol to MDO by the enzyme MdoB. (2) Diacylglycerol kinase converts the diacylglycerol to phosphatidic acid, which can regenerate the phosphatidylglycerol (see Fig. 6). Phosphatidylethanolamine cycling involves (3) the transfer of an acyl chain to membrane lipoprotein and (4) re-esterification of the 1-position by 2-acylgiycerophosphoethanolamine (Aas).

Wilson and Rinne (1976) have supplied soybean cotyledons with labeled acetate and labeled glycerol. Phosphatidic acid and DG turned over rapidly, as might be expected (half-times of 6 min). Half-times of 30-60 min were calculated for PC, PE, and Pi, but inspection of the data shows relatively little change in specific activity after 60 min. Moore (1977) examined phospholipid turnover in soybean suspension cultures and found much longer half-times than Wilson and Rinne (1976). Phosphatidylcholine labeled with choline had a half-life of 36 h, and PE labeled with ethanolamine decayed in three phases with half-lives of 12, 34, and 136 h. 

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