Pancreatic lipase and co-lipase. Interactions and effects of bile salts and other detergents

A colorimetric assay of pancreatic lipase: rapid detection of lipase and colipase separated by gel filtration

A rapid assay for pancreatic lipase (E.C., glycerol-ester hydrolase 3.1.1.3) is described. The assay is based on the color change of a pH indicator as butyric acid is released from the substrate tributyrin. A mixture made with tributyrin and the water soluble components of the assay is ideally suited for use as a rapid test as, for example, when assaying chromatography fractions. Quantitative data can be obtained by measuring the disappearance of absorbance at 557 nm versus a blank reaction. The assay has been used in the rapid preparation of colipase-free lipase and colipase.

Further results on lipase-colipase interactions studied by affinity chromatography

Affinity chromatography of lipase on a colipase-coupled gel was studied in the present paper. The elution volume of the associable lipase increased when the loaded amount decreased. A KD value of 1.9 X 10(-6) M at pH 6.2 was thus deduced. A minimum value of 1.5 X 10(-6) M was obtained at pH 5.1-5.3. Mixed micelles associated with coupled colipase, but no modifications of lipase-colipase interactions took place when mixed micelles were added to the elution buffer. DMMA-modified coupled colipase failed to interact with lipase, owing to the specific orientation of the modified cofactor in the gel.

Inhibition of pancreatic and microbial lipases by proteins

We have compared the effect of several proteins, including melittin, beta-lactoglobulin A, serum albumin, ovalbumin and myoglobin, on the hydrolysis of tributyrin and triolein by lipases from various origins. All proteins tested inactivate pancreatic lipase in absence of colipase and bile salt. Inhibition is not significantly reversed by colipase in absence of bile salt except in systems containing tributyrin and melittin or triolein and beta-lactoglobulin A. In all other cases, activation of pancreatic lipase by colipase in presence of inhibitory protein requires the presence of bile salt. Lipase from Rhizopus delemar is also inhibited by the proteins that inactivate pancreatic lipase. In contrast, the activity of lipase from Rhizopus arrhizus is not affected by the proteins in the same concentration range. Inhibition of lipase activity by amphiphiles such as proteins or detergents appears to be a general phenomenon not directly related to a decrease in tension at the triacylglycerol-water interface. Inhibition could be the result of desorption of lipase from its substrate due to a change in interfacial quality.

Studies on chicken pancreatic lipase and colipase

Lipase and colipase have been purified to homogeneity from chicken pancreatic tissue. The enzyme has a molecular weight (48 000) and catalytic properties similar to those of pancreatic lipase from higher mammals. Hydrolysis of triolein by chicken lipase is strongly inhibited by various bile salts, including sodium taurochenodeoxycholate, which is present in large proportion in chicken bile. Inhibition is reversed by colipase. With triolein as enzyme substrate, in the presence of sodium deoxycholate, no difference was observed in the ability of pure colipase from chicken, horse or pig to fully activate bile-salt-inhibited lipase from the same species. However, kinetic studies of the hydrolysis of a lecithin-stabilized emulsion of triacylglycerol (Intralipid) by chicken lipase show that the lag period is much longer in the presence of porcine colipase than with the chicken cofactor. This might reflect the higher ability of the avian enzyme to associate with colipase from the same species than with mammalian cofactors when the triacylglycerol substrate surface is covered with amphiphilic lecithin. From our study, the chicken pancreatic lipase/colipase system appears to be functionally similar to homologous lipolytic systems from higher mammals. It is then likely that they are of comparable physiological significance in fat digestion in avian and mammalian species.

The production of liquid crystalline product phases by pancreatic lipase in the absence of bile salts. A freeze-fracture study

The hydrolysis of gum arabic-stabilized trioleylglycerol emulsions by pancreatic lipase was examined by freeze-fracture electron microscopy in the absence of bile salts. A sequence of liquid crystalline product phases was produced during the non-equilibrium conditions of hydrolysis. The morphology of the product phases were pH- and droplet size-dependent. At pH 8.3 the initial product phase was composed of homogeneous spherical vesicles regardless of trioleylglycerol drop size. As the reaction progressed the partially hydrolyzed droplets showed a crystalline 'crust' and a true lamellar phase which was often swollen, giving an isotropic appearance to this phase. Some droplets demonstrated a possible transitory hexagonal phase composed of tubular-lamellar elements in close association with the oil phase. These tubular-lamellar elements graded into a lamellar phase at the aqueous/product interface. A cubic phase was not discernible. At pH 7.0 a single phase was seen which covered the drop surface with an amorphous layered 'crust'. The significance of these phases is discussed in relation to those produced by pure and mixed lipids under equilibrium conditions.

Comparison of an open and a closed tube system for collection of jejunal juice

When jejunal juice is obtained by means of open pernasal tubes, the risk of the aspirates being contaminated is presumably high. The present study compares jejunal aspirates obtained from an open and from a closed tube system. Ten patients suspected of having abnormal jejunal flora and five healthy human volunteers were investigated. The pH values of aspirates obtained from the open tubes were significantly lower than the values registered in aspirates from the closed tube system, with a median difference of 0.70 (p less than 0.02). No differences between the two types of aspirate were registered with regard to total number of bacteria, number of bacterial species, lipase, total protein, total amylase or its fractions of pancreatic and salivary isoamylases. For the investigation of pH-sensitive substances in jejunal juice, a closed tube system is therefore recommended, whereas the use of such a device does not seem necessary for the study of bacterial microflora and pancreatic enzymes.

Evolutionary studies on pancreatic colipase

In this evolutionary study the following criteria have been used to prove the existence of colipase: 1. It restores the activity of human and porcine pancreatic lipase inhibited by bile salt. 2. It cross-reacts with antisera to human and porcine colipases. 3. Its restoration of lipase activity, inhibited by bile salt, in the tributyrin assay system, is prevented by antiserum to colipase. 4. It is a heat-stable, low-molecular-weight protein (molecular weight about 10 000 by gel-filtration). The occurrence of colipase has been verified in the exocrine pancreatic cells from hagfish (Myxine glutinosa), ratfish (Chimaera monstrosa), rayfish (Raja radiata). Greenland shark (Somnius microcephalus) and dogfish (Squalus acanthius). No colipase activity could be found in the gastric juice of crayfish (Pacifastacus leniusculus). These results indicate that colipase envolved in the vertebrates before the organized exocrine pancreatic gland and occurred simultaneously with the bile salts/bile alcohols.

Binding between immobilized anti-colipase purified antibodies and colipase. Radioimmunoassay of colipase from pig plasma and pancreatic juice

Procedures for purification of porcine colipase II (Gly6-Gly89) and for obtaining purified anti-colipase antibodies are described. The interactions between antibodies immobilized on an Ultrogel AcA 22 column and colipase were investigated and colipase radioimmunoassay carried out. The immobilized antibody-colipase binding was preserved in the presence of mixed micelles, lipase, or both when added to the elution mixture. Bound colipase maintained its capability of interacting with mixed micelles, but not with lipase in either the presence or the absence of mixed micelles. It could be inferred that the antigenic site(s) is independent of the interfacial recognition site and close to the site of lipase recognition. Results are reported suggesting that one or both colipase histidyl residue-containing sequences are involved as antigenic determinant(s). Immunoreactive colipase, bound to a macromolecular protein complex, was found in the plasma of pig. This finding could be explained by an endocrine 'leakage' of colipase from the exocrine pancreatic cell rather than by passage through the intestinal mucosa.

The temperature-dependent interfacial inactivation of porcine pancreatic lipase. Effect of colipase and bile salts

This paper confirms and extends the previous observation that colipase and bile salts stabilize pancreatic lipase against inactivation at its water/substrate interface. It is shown that colipase and bile salts above their critical micellar concentration offer better protection than either of them alone. Colipase has no effect on the catalytic efficiency of lipase against an emulsified substrate in the absence or presence of bile salts. Its reported activation of pancreatic lipolysis at high temperatures in the absence of bile salts is, most likely, fully explained by its protective effect on lipase inactivation. Colipase at high concentrations relative to lipase inhibits the enzyme activity in a competitive fashion. The temperature-dependent surface inactivation of lipase has certain consequences for the methodology of lipase activity determination.

Measurement of the binding of human colipase to human lipase and lipase substrates

Equilibrium partition in an aqueous two-phase system was the method used for quantitative determinations of the binding between human colipase and human lipase and three triacylglycerol substrates: Intralipid tributyrin and triolein. The measurements were performed in a dextran/polyethyleneglycol system at pH 7.0 in the presence of 2 mM sodium taurodeoxycholate and 150 mM NaCL. The binding of colipase to lipase had a dissociation constant Kd = 4.8 . 10(-8) M. The dissociation constants for the binding of colipase to Intralipid, tributyrin and triolein were found to be 2.10(-7) M, 4.8 . 10(-8) M and 6.2 . 10(-8) M, respectively.

Phenethylamine inhibitors of partially purified rat and human pancreatic lipase

Methodology for the preparation of rat and human pancreatic lipase (EC 3.1.1.3) is described, which resulted in good yield of partially purified, stable enzyme useful for kinetic studies. Apparent Km values for the rat (6.5 mM) and human (3.5 mM) enzyme were determined with triolein as the substrate. Several compounds of the phenethylamine class were found to be inhibitors of both rat and human pancreatic lipase. The structural feature in the phenethylamine series tested, which appeared to be necessary for lipase inhibition, was a halogenated substituent on the 3 or 4 position of the aromatic ring as in flutiorex, fenfluramine, N-benzyl-beta-methoxy-3-(trifluoromethyl)phenethylamine (I), chlorphentermine and p-chloroamphetamine. A chloro group at the 2 position was ineffective (chlortermine). Alterations in the ethylamine portion of the molecule did not cause significant changes in the inhibitory properties of the active phenethylamines.

Importance of the N-terminal sequence in porcine pancreatic colipase

Colipase exists in pancreatic juice in a pro-form which is activated by limited trypsin hydrolysis. During this activation, the N-terminal pentapeptide 1Val-Pro-Asp-Pro-5Arg is cleaved. The new N-terminal sequence formed, 6Gly-Ile-Ile-Ile-10Asn, contains three isoleucine residues. The importance of these for stimulating lipase activity has been investigated by successive Edman degradation of epsilon-acetimidolysine residues followed by limited trypsin hydrolysis. The epsilon-amidinated colipase obtained was fully active both with a phospholipid-covered triacylglycerol (Intralipid) and tributyrin as substrate. After removal of the three isoleucine residues, the activity of colipase was lost with Intralipid but not with tributyrin as substrate. The shortened colipases regained their Intralipid activity upon addition of long-chain fatty acids. The binding of colipase to lipase was not affected by removal of the isoleucine residues.

The identity and properties of two forms of activated colipase from porcine pancreas

Colipase is excreted as a procolipase, colipase101. It is activated by low concentrations of trypsin, hydrolyzing the N-terminal pentapeptide. With higher concentrations of trypsin or in the presence of Ca2+ a smaller form of colipase containing 85 amino acids, appears. It has glycine as the N-terminal and arginine as the C-terminal amino acid residue and has lost 11 amino acids in the C-terminal chain. The ability of colipase85 to activate lipase with tributyrin as substrate is about the same as for colipase96 and procolipase. With fenfluramine, an anoretic agent, added to the tributyrin colipase assay system, the specific activities of colipase96 and colipase85 are similar and about five times higher than that of colipase101. With intralipid as substrate colipase85 enables lipase to reach the triacylglycerol substrate more rapidly than colipase96, having about six times shorter lagtime for a given concentration. Colipase84, obtained by splitting off the C-terminal arginine from colipase85, has a lagtime somewhere between colipase85 and colipase96, pointing to the importance of arginine85 for Intralipid activity. The binding between lipase and colipase has about the same strength for procolipase, colipase96 and for colipase85, Kd being about 10(-6) M either in buffer or in the presence of 2 mM taurodeoxycholate at pH 7. Addition of long chain fatty acids in the presence of bile salts increases the binding strength between colipase and lipase 100-fold, both for colipase96 and colipase85.

[Effect of the addition of hog pancreatic colipase on the permeability to glucose and the phase transition of phosphatidyl choline liposomes]

An interaction between porcine pancreatic coli-pase and lecithin liposomes is demonstrated by gel filtration assays. The extent of the colipase penetration into the phospholipid bilayer was assessed by permeability and calorimetry studies carried out on the liposome colipase complex. The addition of colipase to liposomes induces a three fold increase in the permeability to [6-H3] glucose. This result reflects a perturbation in the bilayer which may be the consequence of the colipase interaction. The phase transition temperature is not modified by the added colipase. This observation suggests that the perturbation brought by the protein does not affect the acyl chain packing of the bulk lipid. On the other hand the enthalpy of transition (delta H) is decreased from 8.9 to 7.8 kcal/mole by the addition of colipase to the lipid. This could be explained by the interaction of the colipase with neighbouring acyl chains which do not participate in the cooperative melting of the bulk lipid. In agreement with previous spectrophotometric observations, the present results are indicative of hydrophobic interactions between colipase and bilayer hydrocarbon chains.

Purification of two lipases with high phospholipase A1 activity from guinea-pig pancreas

1. Two cationic lipases (Ia and Ib) were purified from homogenates of fresh guinea-pig pancreas by ion-exchange chromatography on DEAE-Sepharose and CM-Sepharose (twice for the latter) followed by gel filtration on Sephadex G-100. 2. Both enzymes were homogeneous upon polyacrylamide gel electrophoresis. Their molecular weights are 37,000 and 42,000 for lipases Ia and Ib, respectively, as determined by gel filtration on Sephadex G-100. Very close values for isoelectric points were found in the pH range 9.3-9.4. 3. The cationic lipases are characterized by a high phospholipase A activity (500 IU/mg protein using a potentiometric assay with egg yolk lecithin as substrate), resulting in an unusual phospholipase/lipase activity ratio of 1. 4. Using doubly labelled phosphatidylcholine, a specificity, A1, was described for the two enzymes, which are unaffected by N-ethylmaleimide, diisopropylfluorophosphate and p-bromophenacylbromide. The enzymes are insensitive to EDTA and slightly inhibited by CaCl2 and MgCl2, whereas sodium deoxycholate is required for maximal activity.

Enhanced activity of brain lipase in the presence of adrenocorticotrophic hormone. Comparison with a colipase effect

The characteristics of the pH-dependent stimulatory influence of adrenocorticotrophic hormone (ACTH) on lipolysis (Arnaud, J., Nobili, O. and Boyer, J. (1980) Biochim, Biophys. Acta 617, 524-528) were investigated further. ACTH enhanced 7-30 times the rates of hydrolysis of emulsified trioleoylglycerol by a rat brain lipase, when added to the medium both before and after the enzyme. When lipase activity was inhibited by sodium taurocholate, ACTH fully reversed the inhibition at bile salt concentration up to 2 mM. The reactivation process followed a sharp S-shaped pattern, leveling off at about 10(-4) M ACTH. With and without bile salt, the stimulatory effect of ACTH culminated at pH 5.75, and was dependent on the presence of trace amount of a water-insoluble solvent in the substrate emulsion. Taken together, the results suggest that ACTH acts at the lipid-water interface in facilitating the enzyme-substrate interaction. The relevance of the hormonal influence to a colipase-like effect is discussed.

Lipid absorption and intestinal lipoprotein formation

Lipid absorption is a complex process which involves coordinated gastric, intestinal, biliary and pancreatic function. Emulsification of dietary lipid occurs in the stomach and upper intestine where a series of enzymic events also occur. Phospholipids are digested by phospholipases. Colipase anchors lipase to the emulsion surface overcoming the interfering effect of bile salts. The products of lipolysis, monoglycerides and fatty acids, are removed from the emulsion surface by bile salts in the form of mixed micelles which transport lipid digestive products across the unstirred water layer to the epithelial cell. Within the intestinal epithelial cell a series of synthetic events occur resulting in the formation of chylomicrons and very low density lipoprotein (VLDL). Chylomicrons consists of an oily core of triglyceride surrounded by a membrane of phospholipids, free cholesterol and apoproteins which maintain the solubility of the particle in plasma. Chylomicrons from both experimental animals and man have specific apoproteins associated with them. These proteins include apoA-I, the major protein of plasma high density lipoproteins. During chylomicron metabolism, apoA-I and phospholipid from the chylomicron surface contribute to plasma high density lipoproteins. Other chylomicron apoproteins include apoB and apoA-IV, which are synthesized in the intestine, and apoC and apoE which are absorbed onto the chylomicron surface from other lipoproteins. The intestines also synthesizes, very low density sized particles (VLDL) while fasting and during lipid absorption. There is evidence that the intestine also synthesizes high density lipoproteins. The intestine has recently been recognized as a major site of synthesis of plasma lipoproteins and apoproteins, especially apoA-I for plasma high density lipoproteins.

Effect of taurodeoxycholate, colipase and temperature on the interfacial inactivation of porcine pancreatic lipase

Beside their inhibitory effect upon lipase adsorption, bile salts at low concentration (around 0.2 mM) have repeatedly been shown to enhance lipolysis slightly. From the data reported in this paper, this activation has been attributed to a stabilization of the adsorbed lipase brought about by low concentrations of bile salts. This hypothesis relies on the following observations. (a) For a given temperature, the activation by bile salts depends on the substrate. It is maximum for trihexanoin (trihexanoylglycerol) and does not exist for tripropionin (tripropionylglycerol). (b) In the absence of bile salts, the optimal activities are obtained for different temperatures depending on the substrate. (c) For a given substrate, the activation by a low concentration of bile salts depends on the temperature. It increases when the temperature is raised (up to 35-40 degrees C) and completely disappears at a sufficiently low temperature (around 10 degrees C). (d) This temperature effect does not seem to be due to a modification of the physical parameters of the interface as measured by the interfacial tension. (r) Colipase, like bile salts, increases the lipase activity on short-chain triglycerides but only at high temperature when lipase denaturation occurs. It has no influence upon the activity when the temperature is sufficiently low (around 10 degrees C).

The influence of bile salts and bile lipoprotein complex on pancreatic lipase hydrolysis of monomolecular films

We report a new technique which allows us to follow the lipolysis of monomolecular films in the presence of bile salts by using a 'zero-order' trough (Verger, R. and de Haas, G.H. (1973) Chem. Phys. Lipids 10, 127). The effects of bile salts, the bile lipoprotein complex and colipase on pancreatic lipase hydrolysis of rac-1,2-didodecanoylglycerol films were studied at different surface pressures. Taking into account previous studies, lipase activity was interpreted as a function of its degree of binding to the bile lipoprotein complex.

Measurement of the binding of colipase to a triacylglycerol substrate

The binding between colipase and two triacylglycerol substrates, tributyrin and Intralipid, in the presence of bile salts have been determined quantitatively by a method based on equilibrium partition in an aqueous two-phase system. In the model proposed the triacylglycerol, in the form of spherical droplets covered with bile salt, is assumed to have a certain number of independent binding sites at the surface for colipase. The binding of colipase to tributyrin at pH 7.0 in the presence of 4 mM sodium taurodeoxycholate and 150 mM NaCl had a dissociation constant Kd = 3.3 . 10(-7) M; the concentration of binding sites was 1.2 . 10(-6) M in a 102 mM tributyrin emulsion. When tributyrin was dispersed in 1 mM and 12 mM sodium taurodeoxycholate the dissociation constant was somewhat higher, 6.3 . 10(-7) M and 6.0 . 10(-7) M, respectively. Thus the binding strength was optimal at 4 mM sodium taurodeoxycholate. At the same time the concentration of binding sites decreased from 4.1 . 10(-6) M for 1 mM sodium taurodeoxycholate to 1.4 . 10(-6) M for 12 mM sodium taurodeoxycholate. This indicated that at higher bile salt concentration the bile salt acted as non-competitive inhibitors on the binding of colipase to the substrate, thus binding to other sites than colipase to the substrate. The binding of colipase to Intralipid, an emulsion of a long-chain triacylglycerol stabilized with phosphatidylcholine and glycerol, was more complex with indications of several different binding sites with different affinity. The majority of these had a dissociation constant Kd = 1.2 . 10(-6) M in the presence of 4 mM sodium taurodeoxycholate and 150 mM. With each droplet having a diameter of 10(-4) cm, the number of binding sites on each droplet was determined to 1.96 . 10(5) and the average area available for each colipase molecule to 1600 A at saturation. Colipase on denaturation has a surface of 1320 A.

Interaction of porcine pancreatic colipase with a nonionic detergent, Triton X-100: spectrophotometric studies

Strong perturbation of the ultraviolet spectrum of the tyrosines of porcine pancreatic colipase A is observed in the presence of Triton X-100 at concentration above the critical micellar concentration. Spectrophotometric titration of the phenolic groups of the protein shows that the apparent pKa value for two tyrosines is about 10.3, while the third tyrosine has a higher pKa value above 11.6. This residue is still protonated at pH 13 in the presence of Triton X-100. All perturbations induced by the nonionic detergent can be interpreted as resulting from interactions between colipase and Triton X-100 molecules at a hydrophobic site of the protein that includes the tyrosine residues. Results obtained in studies with Triton X-100 are similar to those already reported by Sari et al. (Eur. J. Biochem. 58:561 (1975) on the interaction of colipase with taurodeoxycholate. It is likely that the binding of both types of detergent occurs at the same specific site on the protein molecule. Data presented in this communication give further support to the hypothesis that a hydrophobic domain (residues 49-57), including all three tyrosines of the colipase molecule, participate to the well characterized interaction of the lipase cofactor with triglycerides at lipid-water interfaces.

Lipase-colipase interactions during gel filtration. High and low affinity binding situations

The interaction of porcine pancreatic lipase and colipase was studied during gel filtration in columns eluted with a variety of buffers. High and low affinity binding situations were observed under different conditions. Low affinity binding could only be detected at the high lipase-colipase concentrations encountered during batch purification (10(-3)-10(-4) M). Even in this situation the rapid dissociation of the weak complex during filtration resulted in considerable separation of the two proteins. High affinity binding of lipase to colipase was observed at protein eluant concentrations as low as 10(-8) M on columns equilibrated with oleic acid-taurodeoxycholate mixed micelles. This binding did not take place on columns equilibrated with simple bile salt and mixed phosphatidylcholine-cholesterol-bile salt micelles. Colipase alone exhibited strong binding to phosphatidylcholine and fatty acid mixed bile salt micelles when applied together in a sample on columns eluted with pure bile salt micelles, lipase did not. The relevance of the high affinity complex to the lipase . colipase . substrate complex is discussed.

Inhibition of lipase adsorption at interfaces. Role of bile salt micelles and colipase

The effects of bile salts and colipase on the adsorption of lipase at an interface were studied by hydrophobic affinity chromatography on phenyl- and octyl-Sepharose. In the absence of bile salts, lipase or colipase binds separately to the gel. This is unchanged in the presence of adsorbed bile salts, when one bile salt molecule is associated per hydrophobic ligand. The same data are obtained in the presence of monomeric bile salt solutions. In contrast, lipase adsorption is totally prevented in a micellar bile salt solution. These results favor the idea that the formation of a lipase-bile salt complex in solution is responsible for the lack of interfacial lipase adsorption.

Role of feeding on lipase activity in gastric contents

Lipase activity was recorded in gastric contents collected from healthy term and preterm neonates. In contrast to pancreatic lipase activity this lipase activity was higher at pH 5.5 than at pH 8.0 and it was more resistent to acid inactivation. Lipase activity was found in gastric contents from all infants who were regularly fed, but was not present in gastric contents from some infants when collected before regular feeding was established. During test meals lipase activity in gastric contents increased considerably in all infants studied. During such a test meal there was a progressive relative decrease in triglycerides whilst diglycerides showed a relative increase suggesting an active lipolytic process in the stomach. An assay procedure for determination of lipase activity in gastric contents is also described.