Pancreatic lipolytic enzymes

B. Stcmby, A. NOnon, T. Mel in, and B. Borgstidm. Pancreatic lipolytic enzymes in human duodenal contents. Stand J. Gastroenterol, 26 859 (1991). 

Hydrolysis of esterified lipids is essential in order for lipid absorption to occur. Anatomically, lipolysis begins in the stomach where a limited amount of partial hydrolysis of triglycerides provides more polar lipids (fatty acids and partial glycerides) to assist in emulsification. A lingual lipase is thought to be involved in this process. The net result of this gastric phase of fat digestion is the initiation of lipolysis and the preparation of a stable emulsion on which the major pancreatic lipolytic enzymes can act in the milieu of the small intestine. 

It is dear that the interconnection between the activities of the different lipolytic enzymes, where the first enzyme modifies the physicochemical state of the lipid substrate in such a way that it becomes available to another enzyme, is not only of prime importance for lipid digestion, but also results in a broad synergism between gastric lipase, colipase, pancreatic lipase, phospholipase As. calcium, caiboxylester Lipase, bite salts, and substrate interraecK tes [55,62-64]. 

Specificity for certain fatty acids by some lipolytic enzymes has been demonstrated. Pancreatic lipase and milk lipase are broad-spectrum enzymes and show no specificity for any of the fatty acids found in fats. Instead, the fatty acids that are released from... 

In the remainder of the paper, I concentrate on the two best-known lipolytic enzymes—pancreatic lipase and phospholipase 2—and then speculate on the special nature of lipolytic reactions and how lipolytic enzymes diflFer from hydrolases. 

H-5) Pancreatitis. Pancreatic lipase is a lipolytic enzyme that releases fatty acids from glycerides. It, as well as proteolytic enzymes produced by the pancreas, are normally, as a cell-protective measure, kept in inactive (zymogen) form in h.e pancreatic cell. Pancreatitis can activate these enzymes with resultant pancreatic damage. 

It is seen that for the proteolytic power of the pancreatic juice, the same order of classification is obtained as was the case with the gastric juice. Bread causes the maximum production of trypsin, meat is next in order, and then milk. As regards amylase, bread requires a large amount, meat less, and milk still less. For the lipolytic enzyme, it is milk, rich in fatty matter, wliich will require the largest quantity. 

Leather industry uses proteolytic and lipolytic enzymes in leather processing. The use of these enzymes is associated with the structure of animal skin as a raw material. Enzymes are used to remove unwanted parts. Alkaline proteases are added in the soaking phase. This improves water uptake by the dry skins, removal and degradation of protein, dirt, and fats and reduces the processing time. In some cases, pancreatic trypsin is also used in this phase. 

Pancreatic amylase Infants with this deficiency begin life unable to digest starch. However, after a few months, the pancreas starts to produce sufficient amylase. Adults produce such an excess of this enzyme that even patients with severe pancreatitis (who are unable to produce sufficient lipolytic or proteolytic enzymes) can produce sufficient amylase to cope with a normal amount of starch in the diet. 

Exocrine pancreatic insufficiency is most commonly caused by cystic fibrosis, chronic pancreatitis, or pancreatic resection. When secretion of pancreatic enzymes falls below 10% of normal, fat and protein digestion is impaired and can lead to steatorrhea, azotorrhea, vitamin malabsorption, and weight loss. Pancreatic enzyme supplements, which contain a mixture of amylase, lipase, and proteases, are the mainstay of treatment for pancreatic enzyme insufficiency. Two major types of preparations in use are pancreatin and pancrelipase. Pancreatin is an alcohol-derived extract of hog pancreas with relatively low concentrations of lipase and proteolytic enzymes, whereas pancrelipase is an enriched preparation. On a per-weight basis, pancrelipase has approximately 12 times the lipolytic activity and more than 4 times the proteolytic activity of pancreatin. Consequently, pancreatin is no longer in common clinical use. Only pancrelipase is discussed here. 

Four major enzyme groups are secreted lipolytic, proteolytic, amylolytic, and nucleic acid splitting enzymes. These pancreatic enzymes, some of which are secreted in multipile forms, possess specificities complementary to die intestinal membrane-bound enzymes (Tabic 1). Fresh, uncontsnkinated pancreatic juice is without proteolytic activity because these enzymes am in the form of inactive zymogens. An important fraction of the calcium in pancreatic juice accompanies the enzymes, especially ct-amylase. Human pancreatic juice is moat dose to that of the pig, with high proportions of lipase and a-amylase in comparison with other mammals [1]. Therefore, pig pancreas extract, pancreatin, has up to now been die oreferred enzvme source for therapeutic tuncreas substitution. 

Porcine pancreas and porcine pancreatic juice appear to contain a single protein endowed with lipolytic activity. As stated earlier, this protein corresponds to about 2.5 % of the total proteins of the juice. Its molecular activity (turnover number) is likely to be higher than 300,000 under the conditions of the test. Shortage of pure material has thus far prevented any investigation of its molecular properties. It is merely known to be quite soluble in water, to have an isoelectric point of 5.2 in 0.025 M acetate buffer, and to give a conventional protein spectrum. Lipase present in pancreatic juice is likely to be identical with the enzyme extracted from pancreatin. 

Tab. 10.1 Maximum specific activities of HGL, DGL, HPL and pancreatic extracts (Creon ) on various triglycerides. Specific activities are expressed in international units (1 LJ = lpmol of free fatty acid released per minute) per mg of pure enzyme, except for Creon for which specific activities are expressed in U per mg of pancreatic extract (PE). One Creon 25000 capsule contains 500 mg pancreatic extract and 25000 lipase units measured using olive oil-gum arabic as substrate. This lipolytic activity corresponds to around 8-9 mg of active pancreatic lipase in one capsule of Creon 25000 .

For pancreatic lipase to be active, an additional protein, termed colipase, is required (B26). Pure pancreatic lipase is inhibited by bile salts in concentrations exceeding their critical micellar concentrations (B27). The fiinc-tion of coUpase is to restore lipase activity in the presence of bile salts. Although colipase by itself has no lipolytic activity (B27), defective fot digestion and absorption occur if either lipase or colipase activity is low in the small intestine. Patients with steatorrhea due to either isolated lipase deficiency (F4) or isolated cohpase deficiency (H16) have been reported. A lipase which requires bile acids for activity is human milk lipase (Ol). This enzyme comprises 1% of the protein of human milk, but is inactive i ainst milk fots until its activity is stimulated by bile acids in the small intestine. 

The two common preparations of pancreatic enzymes for replacement therapy are obtained from the pancreas of the hog (Sus scrofa Linne var. domesticus Gray). Pancreatin (Don-nazyme, others) contains amylase, lipase, and protease, and has one-twelfth of the lipolytic activity of pancrelipase, on a weight-by-weight basis. Pancrelipase is more commonly used and is available in uncoated forms, as weU as capsules containing enteric-coated microspheres and enteric-coated microtablets, which withstand gastric acid (lipase is inactivated by acid) and disintegrate at pH > 6. Familiarity with these two classes of preparations is important clinically. 

When the secretion of the pancreatic juice is caused by means of repeated injections of secretin, it is found that during the draining, which may last for 10 or 12 hours, the enzyme content of the juice constantly diminishes. Yet, the decrease is much greater for the lipolytic and amylolytic powers than for the proteolytic power. At the same time, the alkalinity of the juice also decreases. With respect to this last variation, the following figures, estimated in fractions of normal liquor, are given by L. Morel and Terroine. 

Gerber has detected a proteolytic enzyme, capable of coagulating milk and peptonizing albuminoid materials, in the sap of Broussonetia papyrifera L. (Paper Mulberry). The sap contains three kinds of enzymes one, amylolytic one, lipolytic and one, proteolytic. The enzyme composition of this juice resembles that of the pancreatic juice. These enzymes come into play in the chemistry of the plant from the moment when the reserves are utilized to form the young leaves. Gerber has found that this vegetable pancreatic juice diminished in activity in autumn and winter, but without having its proteolytic power disappear completely. The relative content in these three active... 

---