Enzymes phospholipases

The venoms of poisonous snakes contain (among other things) a class of enzymes known as phospholipases, enzymes that cause the breakdown of phospholipids. For example, the venoms of the eastern diamondback rattlesnake (Crotalus adamanteus) and the Indian cobra Naja naja) both contain phospholipase Ag, which catalyzes the hydrolysis of fatty acids at the C-2 position of glyc-erophospholipids. 

The fatty acid is a precursor for fatty acid derived messengers, after it is released from a membrane phospholipid by the action of a phospholipase enzyme (see below). 

In Uver, adrenaline binds to the a-receptor, and the hormone-receptor complex activates a membrane-bound phospholipase enzyme which hydrolyses the phospholipid phosphatidylinositol 4,5-bisphosphate. This produces two messengers, inositol trisphosphate (IP3) and diacylglycerol (DAG) (Figure 12.5). The increase in IP3 stimulates release of Ca ions from the endoplasmic reticulum into the cytosol, the effect of which is glycogen breakdown and release into the blood (see Figure 12.5 and Chapter 6). 

In a commercial process, it is desirable to control the reaction so that just one of the fatty acids is cleaved from the phospholipid molecule. As acid or base hydrolysis is nonspecific and very difficult to control, enzymes are usually preferred for most applications (58). A number of phospholipase enzymes are available (i.e., phospholipase Ai or phospholipase A2). 

Another aspect of heating soybeans in particular is the impact on the phospholipase enzyme. The phospholipase enzyme is activated at approximately 55°C and remains activated up to approximately 100°C. In this temperature range, and with sufficient exposed surface area and time, the phospholipase enzyme modifies a portion of the phospatides in the oil fraction by splitting off the non-fatty acid moiety (16). The resultant calcium and magnesium salts of phosphatidic acids that are formed tend to be more oil-soluble than water-soluble, thereby converting phospatides from a hydratable form to a nonhydratable form (16). This has a resultant impact on the quantities of acid, caustic and silica needed to reduce the phosphorus content of the soybean oil in the downstream degumming and refining unit operations. 

Wet extmders are also used ahead of a number of soybean solvent extraction plants. In plants with undersized extractors, the energy used by the extruder can be compensated by additional oil yield from the extractor. Steam consumption is reduced in the desolventizer toaster. Additionally, the wet extruder in a soybean plant increases temperature sufficiently to stop the phospholipase enzyme from converting additional hydratable phosphatides into nonhydratable phosphatides. This reduces acid, caustic, and silica consumption in the downstream refinery. However, in soybean plants with adequately sized extractors where potential oil yield... 

The relative abundance of a particular phospholipid in the two leaflets of a plasma membrane can be determined on the basis of its susceptibility to hydrolysis by phospholipases, enzymes that cleave various bonds in the hydrophilic ends of phospholipids (Figure 5-9). Phospholipids in the cytosolic leaflet are resistant to hydrolysis by phospholipases added to the external medium because the enzymes cannot penetrate to the cytosolic face of the plasma membrane. 

Enzymatic degumming was first introduced by Lurgi as the EnzyMax technology. " Reduced gum volume due to formation of water-soluble lyso-phosphatide, avoidance of soap stock formation, hence increased oil yield, and reduced environmental impact have made enzymatic degumming based on phospholipase enzyme an alternative to conventional degumming with increasing commercial interest (Figure 9.1.8). ... 

Identification can be confirmed by the use of a number of commercially available phospholipase enzymes. The stereospecificity of the enzymes also allows the stereochemistry of the lipid to be established. The action of such enzymes is detailed in Table 6.6 and incubation details are given in Kates (1972) and Lowenstein (1969). 

Note As shown in Figure 3.27, postmortem degradation of GPLs was observed by IMS within 15 min in a series of mouse brains extracted at different times (15, 30, 60, and 120 min). This is presumably because of stimulation of phospholipase enzymes under ischemic conditions [64,65]. 

This is presumably because of stimulation of phospholipase enzymes under ischemic conditions (37, 38). 

Ghosh, M., S. Bhattacharyya, and D. K. Bhattacharyya. 2005. Production of Lipase and Phospholipase Enzymes from Pseudomonas Sp. And Their Action on Phospholipids. Journal ofOleo Science 54 (7) 407-411. 

When the mycelial hypha reaches a microfissure, it penetrates the grape. Thns B. cinerea development occnrs mainly in the grape s superficial cell walls. More precisely, the mycelial filaments are located in the middle lamella of the pectoceUulosic ceU walls. The latter are degraded by the enzymes of the fnngns (pectinolytic, cellulasic complex, protease and phospholipase enzymes). 

This study served to verify our previous report (2) that phospholipase activity in potato leaves is stimulated by protein phosphorylation and by calmodulin. More importantly, it demonstrated that the degree of stimulation of the same enzyme activity by proteolytic activation was even greater than the degree of stimulation with protein kinase or calmodulin. Further work is required in order to elucidate the mechanisms of these three types of stimulation. We previously suggested that the calmodulin and protein kinase stimulations could be explained by phosphorylation of a phospholipase enzyme by an endogenous calmodulin-stimulated protein kinase (2). However, in light of the current evidence of proteolytic activation, a more complex mechanism of activation is necessary to best explain the three types of activation. 

Figure 4.1 Indication of bonds on a phospholipid molecule that are hydrolyzed by various phospholipase enzymes. X = H, choline, elhanolamine, inositol.

---