Secreted phospholipases enzymes other

I various subcellular locations within eukaryotic cells. Some of these enzymes are specific for particular polar head-groups others are nonspecific. Phospholipase A2 is a major component of snake venom (cobra and rattlesnake) and is partially involved in the deadly effects of these venoms. Because of the high concentration of phospholipase A2 in these venoms, this enzyme has been studied intensively. The pancreas is also rich in phospholipase A2, which is secreted into the intestine for digestion of dietary phospholipids. 

Among the outer membrane enzymes, OmpT is a special protease that has been implicated in the pathogenicity of bacteria. It is monomeric with the active center pointing to the outside (Vandeputte-Rutten et al., 2001). Another enzyme, the phospholipase A OmpLA, produces holes in the outer membrane when it is activated. The activation process has not yet been clarified, but it is known to require a dimerization of OmpLA in the membrane. The activation by dimer formation has been verified by a crystal structure analysis of an OmpLA dimer that was produced by a reaction with an inhibitor (Snijder et al., 1999). It showed that each active center contained a catalytic triad Ser-His-Asn on one subunit and an ox-anion hole formed by an amide together with a hydrated Ca2+ ion on the other. The active centers are well placed for deacylating lipopolysaccha-rides of the external leaflet of the outer bacterial membrane. OmpLA functions in the secretion of colicins and virulence factors. 

Pancreatic lipase, in the presence of bile salts and coUpase, acts at the oil-water interface of the triglyceride emulsion to produce fatty acids and 2-monoacylglycerols. Cohpase is secreted in pancreatic juice as an inactive proenzyme, which is converted to the active form by trypsin. Other significant enzymes involved in the breakdown of fats within the intestinal lumen are cholesterol ester hydrolase, phospholipase A, and a nonspecific bile salt-activated lipase. 

Enzyme-rich pancreatic juice which contains several enzymes capable of hydrolysing triacylglycerides and other lipids is secreted from the pancreas and mixed with the chyme. Pancreatic phospholipase Ag hydrolyzes phospholipid, thus producing fatty acids and lyso-phospholipids. Pancreatic triacylglyceride... 

Several examples of bioassay-guided isolation are given in the literature. Recio et al [47] used a topical irritant agent to track the activity during the isolation of the anti-inflammatory triterpenes from Diospyros leucomelas, whereas Cuellar et al. [48] employed a combined system of in vivo and in vitro experiments, consisting of the inhibition of an enzyme activity Fig. (1) . Other authors prefer in vitro models. Ammon and Safayhi [49] used the inhibition of leukotriene formation in rat peritoneal neutrophils to isolate the boswellic acids of gum resin exudate of Boswellia serrata, whereas Takaishi et al. [42] studied the inhibition of interleukin-1 secretion, and Jain et al. [50] studied the in vitro inhibition of phospholipase A2 activity. The main results of these studies are summarised in the pharmacological activity section of this chapter. 

This enzyme (triacylglycerol acyl-hydrolase) has a molecular mass of approximately 42 kDa (Hide, Chan, and Li 1992) and a short half-life of about 1-3 h in dogs. Pancreatic lipase is secreted in its active form, and this activity is enhanced by colipase and bile salts the enzyme hydrolyzes triglycerides to monoglycerides. Other lipases— phospholipase a, phospholipase b, and cholesterol ester hydrolase—are also secreted by the pancreas. 

Pancreatic enzymes a group of at least 12 digestive enzymes, including some of the most investigated of all enzymes Autolysis of the pancreas does not occur, because the proteolytic enzymes, trypsin, chymo-trypsin A and B, elastase and carboxypeptidase A and B, and phospholipase A2 are synthesized and stored in the pancreas as inactive zymogens. The other P. e. require effectors for optimal activity, which are present in the duodenum. Trypsin inhibitors in the pancreatic tissue and secretion afford additional protection against proteolytic destruction by active P.e. With the exception of cholesterol esterase (M, 400,000), the M, of P.e. lie between 13,700 (ribonu-clease) and 50,000 (a-amylase). 

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