Phospholipase phosphatidylglycerol

Glycerophospholipids contain a glycerol skeleton to which two fatty acids are esterified saturated fatty acids occupy mostly sn-position 1, whereas unsaturated fatty acids are mainly present on sn-position 2. The third hydroxyl is linked to a phosphate group to which an organic base is mostly esterified (Fig. 1). The most important components of soybean lecithin are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Phosphatidic acid (PA) may become important due to the presence of phospholipase D this enzyme slowly converts PC into PA in vegetable lecithins. Phosphatidylserine (PS), phosphatidylglycerol (PG), and lyso-phosphatidylcholine (LPC) are known as minor components lysophospholipids contain only one acyl group per molecule. Besides, ether phospholipids occur in which one or both fatty acyl... 

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). 

Phospholipase A2 (snake venom) will attack phosphatidylglycerol smoothly and to completion under conditions previously described in chapter 4. One mole of fatty acid is released per mole of lipid phosphorus. This result supports an sn-3 configuration for the phosphatidic acid portion of the molecule. 

Phospholipase D. An improved biosurfactant and emulsifier is made from lecithin by phospholipase D. The enzyme transphosphatidylates lecithin, converting most of the phosphatidylcholine and phophatidyl-ethanolamine to phosphatidylglycerol (49). 

Phospholipase A1 pldA Outer membrane Phosphatidylethanolamine, phosphatidylglycerol, cardiolipin, and lyso derivatives... 

Fig. 3. Schematic showing potential routes whereby G-proteins may mediate Ca and other ion channels within plant cells. The dashed line (—) separates regulation via activation of PLC and channel gating via IP3 (right hand side) from direct regulation (left hand side) in which G or Gp interact directly with the particular ion channels. Phospholipase D which generates IP2 and phosphatidylglycerol (and by the action of other enzymes IP, and DAG respectively) may also be G-protein regulated but is omitted for clarity.

L.R. Juneja, N. Hibi, N. Inagaki, T. Yamane, and S. Shimizu Comparative study on conversion of phosphatidylcholine to phosphatidylglycerol by cabbage phospholipase D in micelle and emulsion system. Enzyme and Microbial Technology 9 (1987) 350-354. 

G.J. Piazza and W.N. Marmer Conversion of phosphatidylcholine to phosphatidylglycerol with phospholipase D and glycerol. Journal of the American Oil Chemists Society 84 (2007) 645-651. 

Figure 11.14 Phospholipid synthesis in plants. For simplicity the full systematic names for enzymes and co-factor requirements are not given. Details can be found in Mudd (1980). Phosphatidylglycerol is mainly formed in photosynthetic tissues. Methylation pathway to phosphatidylcholine has only been demonstrated in a few plants. Cardiolipin synthesis is probably confined to mitochondria. Other possible sources of diacylglycerol include phospholipase C action, demonstrated in many plants and plant tissues. Reproduced from Harwood and Russell (1984) with permission.

Phospholipase A enzymes - particularly those from snake venoms or digestive secretions - have been widely studied. Phospholipase Ai is found in microsomal and liposomal fractions (cf. Newkirk and Waite, 1971 Gatt, 1968). It specifically deacylates phosphatidylcholine or phosphatidylethanolamine at the 1-position. Both these substrates are hydrolysed at the same rate by the adrenal medulla lysosomal enzyme, but that from brain prefers phosphatidylcholine as substrate. Detergents will increase phosphatidylethanolamine hydrolysis by the brain enzyme. A phospholipase Ai (which is relatively specific for phosphatidylglycerol) has been reported from the spores of some bacteria (Raybin et aL, 1972), but most bacterial enzymes are unspecific for either the 1- or the 2-positions. 

Phospholipase D catalyzes the formation of phosphatidylglycerol and di-phosphatidylglycerol by phosphatidyl transfer ... 

Whether the aoove reactions play any role in lipid biosynthesis is open to question. The naturally occurring phosphatidylglycerol is the optically active -T-j -glycerol enantiomer. Yang et al. (1967) found that the product of transphosphatidylation was a racemic mixture, although more recently Batrakov et al. (1975) found evidence for stereospecificity in the acyl transfer reaction with phospholipase D. 

Although C. welchii preparations can be used to hydrolyse phosphatidylethanolamine, provided that some lysophosphatidylcholine [903] or sphingomyelin [762] is present to activate the enzyme, better results are obtained with the phospholipase C of 6. cereus, which can also be used to prepare diacylglycerols from phosphatidylserine, phosphatidylinositol, phosphatidylglycerol and diphosphatidylglycerol. The author has found the following method to be satisfactory for the purpose [991,1002]. (Note that tris buffer is not suitable). 

Phospholipase D has been extensively studied as a catalyst for the synthesis of phospholipids which are naturally occurring in minor quantities. Phos-phatidylserine [62] and phosphatidylglycerol [63] have been prepared in excellent yields from phosphatidylcholine (the major component in natural extracts) and glycerol and serine, respectively. Alternatively, enrichment in phosphatidylcholine can be achieved by transphosphatidylation under low-water conditions with minimal formation of contaminant phosphatidic acid [64]. Some phospholipase D mediated syntheses have been carried out on a multikilogram scale. 

MGDG, monogalactosyldiacylglycerol PC, phosphatidylcholine PG, phosphatidylglycerol PL, phospholipid PLA2, phospholipase A2 PSI, PSII, photosystem I,II SQDG, sulphoquinovosyldiacylglycerol. 

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