Change in bile salt dependent lipase in human breast milk during extended lactation

Two hundred eighty-one milk samples collected from Zaïrian nonprivileged, undernourished mothers, in series of nine groups from 1 month to 18 months after parturition, and 66 milk samples collected from French privileged mothers in series of four groups from 2 days to 16 months postpartum, were analyzed for their lactose, lipid and protein contents. In addition, the activity of bile salt-dependent lipase (esterase), which may play an important role in the newborn infant's lipids digestion, was measured. After the first month postpartum, independent of the nutritional state of the mother, sugar and protein concentrations were identical. Lipid content of French mothers' milk was lower in transitional milk, but appeared constant in mature milk with an average value of 29.1 +/- 5.8 mg/mL of milk. In Zaïrian mothers' milk, the lipid content of mature milk plateaued at around 50-55 mg/mL independent of the stage of lactation. Bile salt-dependent lipase showed constant esterase activity within the lactation stage in privileged mothers' milk, but decreased by almost 80-90% during the first four months of lactation in undernourished mothers. The data suggest that milk from nonprivileged mothers may lose some of its ability to hydrolyze milk lipid esters, which could also be of consequence to the infant's normal growth in view of its effect on the esters of the lipid-soluble vitamins A, E and D.

Hydrolysis of fluorescent pyrene-acyl esters by human pancreatic carboxylic ester hydrolase and bile salt-stimulated lipase

Fluorescent esters containing pyrenedecanoic acid (P10) or pyrenebutanoic (P4) acid (P4cholesterol, P10cholesterol, P4- and P10-containing triacylglycerols) were synthesized and used as substrates for human pancreatic carboxylic ester hydrolase and bile salt-stimulated lipase from human milk. Both enzymes were purified by immunoaffinity chromatography. All fluorescent pyrene derivatives were hydrolyzed by pancreatic carboxylic ester hydrolase and bile salt-stimulated lipase, but at different rates. The hydrolytic rates of the "short" acyl esters (P4-containing esters) were higher than those of the "long" ones (P10-containing esters). Conditions were optimized for sensitivity of the assay using fluorescent cholesteryl esters. The pH optimum was 7.5-8.0. Sodium cholate exhibited a stronger activating effect than taurocholate or taurodeoxycholate (maximal activation was achieved with 5 mmol/L cholate and with a molar ratio cholesteryl ester/cholate around 1:10). Both pancreatic carboxylic ester hydrolase and bile salt-stimulated lipase from milk were strongly inhibited by the other amphiphiles tested, namely phosphatidylcholine and Triton X-100, and were inactivated by low concentrations (10 mumol/L) of the serine-reactive diethyl-paranitrophenyl phosphate (E600). Both enzymes were strongly inhibited by relatively low concentrations of plasma low density lipoproteins. These studies indicate that the fluorescent esters containing pyrene fatty acids can be used as substrates for assaying and investigating the properties of pancreatic carboxylic ester hydrolase as well as bile salt-stimulated lipase from milk.

A cross-linked complex between horse pancreatic lipase and colipase

The water soluble carbodiimide N-cyclohexyl-N'-2-morpholinoethyl-carbodiimide-methyl-p-toluolsulfona te was found to effectively covalently cross-link pancreatic colipase to lipase as evidenced by Western blotting experiments using antibodies directed either against lipase or colipase. Moreover the resulting covalent complex has a Mr consistent with a stoichiometry of 1 mol colipase per mol lipase. Cross-linked lipase and colipase retain their activity implying a correct covalent binding between the two proteins. The specificity of the lipase-colipase binding was further supported by the very low amount of cross-linked products when lipase or colipase alone were incubated in the presence of carbodiimide. The formation of a covalent lipase-colipase complex in the presence of carbodiimide clearly demonstrates that the binding between both proteins involves ion pairing. Furthermore, the formation of an active covalent complex strongly suggests that the lipase-colipase binding site is distinct from the colipase interfacial recognition site as well as from the lipase catalytic site.

Inhibition of human milk bile-salt-dependent lipase by boronic acids. Implication to the bile salts activator effect

The bile-salt-dependent lipase from human milk, which catalyzes the hydrolysis of the water-soluble substrate 4-nitrophenyl acetate and the water-insoluble substrate tributyrin, is competitively inhibited by phenyl boronic acid. This inhibitor does not interfere with the interaction of lipase either with the siliconized glass beads/water interface or with the activator bile-salt binding site. The boronic acid binds near or at the active site serine, since modification of this residue by diisopropylphosphofluoridate (DFP) was prevented by phenyl boronic acid. Phenyl boronic acid binds 15-fold as tightly to bile-salt-dependent lipase as does 4-nitrophenyl acetate. Therefore, phenyl boronic acid bears analogy to a substrate rather than to a tetrahedral intermediate analog. Bile salts such as sodium taurocholate which are non-essential activators for the milk lipase activity on water-soluble substrates decrease the Km as well as the enzyme inhibitor dissociation constant (Ki). They have a slight effect on kcat. These results are interpreted in terms of an increase of the stability of the enzyme-substrate tetrahedral intermediate and in general of any transition states for the formation and for the decomposition of these intermediates upon the enzyme bile salts interaction.

Human milk bile-salt stimulated lipase: further investigations on the amino-acids residues involved in the catalytic site

The bile-salt-stimulated lipase purified from human skim milk was modified with diisopropyl phosphofluoridate (DFP), N-ethyl-5-phenylisoxazolium-3'-sulfonate and ethoxyformic anhydride. These chemical modifications lead to the following results: (1) the inhibition of the enzyme by DFP is due to the phosphorylation of a single residue, probably a serine residue, which may represent the acylable group of the enzyme; (2) carbethoxylation of histidine residues leads to inhibition of the enzyme activity. Among the nine modified histidine residues, only one is essential for enzyme activity; (3) a free carboxyl group with a pKa of 5.4 is also involved in catalysis. These three essential residues are involved in the enzymatic hydrolysis of substrates whatever their physical state (soluble or emulsified). Upon treatment with DFP as well as with ethoxyformic anhydride, the enzyme remains able to bind to the model interface formed by siliconized glass-beads with almost the same efficiency (Kd between 4.1 and 7.4.10(-8) M) than the native bile-salt-stimulated lipase (Kd = 6.3.10(-8) M). Moreover, the modified and native enzymes occupy the same interfacial area (4000-4600 A2/molecule). By contrast, the enzyme modified by N-ethyl-5-phenylisoxazolium-3'-sulfonate reagent presents an interfacial area close to that of a denatured protein of size (approximately 18,300 A2/molecule) and a Kd more than 20-fold higher than that of the native enzyme. Solvent isotope effects measured on kcat/Km and kcat indicate that the catalytic mechanism of bile-salt-stimulated lipase involves transition states that are stabilized by hydrogen bonds as described in the two-step acylation-deacylation mechanism of serine enzymes.

Crystallization and preliminary X-ray study of horse pancreatic lipase

Horse (Equus caballus) pancreatic lipase (EC 3.1.1.3) has been crystallized using the hanging drop method of vapour diffusion at 20 degrees C. The best crystals were grown from an 8 mg/ml solution in 10 to 20% (w/v) polyethylene glycol 8000, 10 mM-MgCl2, 0.1 M-NaCl, 0.1 M-Mes buffer (pH 5.6). They reach dimensions of 0.8 mm x 0.4 mm x 0.6 mm. X-ray examination of the lipase crystals shows that they are orthorombic with a space group P2(1)2(1)2(1). Their cell dimensions are a = 79.8 A, b = 97.2 A c = 145.3 A. Two molecules per asymmetric unit give a Vm value of 2.82 A3/dalton (56% water content). Lipase crystals strongly diffract to at least 1.8 A resolution. Some molecular properties of horse lipase compared to those of the better-known porcine enzyme are also presented.

Purification of pancreatic carboxylic-ester hydrolase by immunoaffinity and its application to the human bile-salt-stimulated lipase

A column of immobilized antibodies directed against pure human pancreatic carboxylic (cholesterol) ester hydrolase was used to purify in a single step the enzyme from human pancreatic juice as well as carboxylic-ester hydrolases from other species (rat, dog). This immunoaffinity method was also used for the purification of the related bile-salt-stimulated lipase from the human skim milk. The enzymes were homogeneous on SDS-PAGE. The yields obtained were always higher than those previously observed using either conventional or affinity columns. The human and dog carboxylic-ester hydrolases as well as the bile-salt-stimulated lipase, in contrast to the rat enzyme, are glycoproteins. From our results, it can be speculated that these enzymes, which differ in their molecular weight but not in their N-terminal sequences or amino-acid compositions, might have a similar proteic core with a molecular mass between 65 and 75 kDa. The difference in their respective molecular masses might result from a different level of glycosylation of pancreatic carboxylic-ester hydrolases (and milk bile-salt-stimulated lipase).

Human monoclonal antibodies that protect mice against challenge with Pseudomonas aeruginosa

Lymphocytes from healthy volunteers and from cystic fibrosis patients were transformed with Epstein-Barr virus and cultured at a limiting dilution to generate lymphoblastoid cell lines that secreted human monoclonal antibodies specific for lipopolysaccharide (LPS) from Pseudomonas aeruginosa. Three cell lines (RM5, FDD7, and 11F9) produced immunoglobulin M (IgM) antibody species that reacted specifically with P. aeruginosa Fisher immunotypes 2, 4, and 5, respectively, and with LPS extracted from these immunotypes. A fourth cell line (9H10) produced a single IgM antibody species that recognized P. aeruginosa immunotypes 3, 6, and 7 and LPS extracted from them. Monoclonal antibodies secreted by cell lines RM5, FDD7, and 11F9 protected neutropenic mice prophylactically against challenge with P. aeruginosa immunotypes 2, 4, and 5, and those secreted by 9H10 protected against P. aeruginosa immunotypes 3 and 6 but did not protect against immunotype 7. In vivo experiments indicated that antibodies protected mice against infection by increasing the rate of bacterial clearance.

Subcellular localization of cholesterol ester hydrolase in the human intestine

Immunocytochemistry and subcellular fractionation were used to localize the cholesterol ester hydrolase in the human small intestine. A positive immunoreaction, when using antibodies directed against pancreatic cholesterol ester hydrolase, was mainly found in endocytotic vesicles. Moreover, a label by gold particles was observed in intercellular spaces where lymphatic tissue merges. No specific immunoreactivity was obtained with the mucosa when sera directed against human pancreatic chymotrypsinogen and human pancreatic lipase were used. Conventional subcellular fractionation was performed after extensive washing of enterocytes to rule out any possible contamination by pancreatic enzymes. In these conditions a bile salt-dependent cholesterol ester hydrolase activity was detected in the soluble fraction of cells. Data agree with the concept that the intestinal cholesterol ester hydrolase may have a pancreatic origin. The absorption, if any, of this enzyme by enterocytes seems specific since other pancreatic (pro)enzymes tested (lipase, chymotrypsinogen) are not detected in these cells.

The inhibition of phospholipase A2 by manoalide and manoalide analogues

Manoalide, a natural product from sponge, displays anti-inflammatory activity in vivo. Previous work has shown that manoalide is also a potent covalent inhibitor of the extracellular phospholipase A2 from cobra venom and that the inhibition correlated with a pH-dependent change in manoalide (Lombardo and Dennis (1985) J. Biol. Chem. 260, 7234-7240). Manoalide contains two rings and the opening of either would produce an alpha,beta-unsaturated aldehyde. The cobra venom phospholipase A2 may be able to catalyze the opening or isomerization of one of these rings, raising the possibility that manoalide is acting as a suicide substrate. To ascertain the role of the gamma-lactone ring in the inhibition, we have now investigated a synthetic manoalide analogue, 3(cis,cis-7,10)-hexadecadienyl-4-hydroxy-2-butenolide (HDHB) which contains only the alpha,beta-unsaturated gamma-lactone ring. We have found that the closed and open forms are in rapid equilibrium between pH 4 and 9 with the cyclic form being preferred at acidic pH values and the open cis form preferred at pH 9.5. When the pH is raised above 12, the alpha,beta double bond isomerizes to form trans-HDHB. Once the trans compound is formed, it is stable at all pH values and does not recyclize to the gamma-lactone ring. The observed pKa of 7.7 found for the inhibition of manoalide agrees well with the transition of the closed to the cis form of the gamma-lactone ring. Kinetic experiments with the HDHB compound show that under conditions in which the cis and closed form of the inhibitor are present in equal molar ratios, HDHB is not an irreversible inhibitor, but reversibly competes with substrate. However, the kinetics of this inhibition are complex and do not follow either pure competitive or non-competitive inhibition. The trans-HDHB exhibits similar complex kinetic but is several times more potent. The distinct differences between the behavior of manoalide and HDHB clearly indicate that while the gamma-lactone ring may play an important role in manoalide inhibition, it alone does not produce irreversible inhibition.

Rate-determining step in phospholipase A2 mechanism. 18O isotope exchange determined by 13C NMR

H2(18)O isotope exchange into specifically 13C-labeled substrate was used to obtain information on the rate-limiting step in the action of the phospholipase A2 from the venom of the Indian cobra (Naja naja naja). Incorporation of 18O was detected by the effect of 18O on 13C chemical shifts in 13C NMR. The enzymatic hydrolysis of a micellar phosphatidylcholine analogue of platelet-activating factor 1-alkyl-2-[1-13C]lauroyl-sn-glycero-3-phosphorylcholine proceeds by an O-acyl cleavage of the sn-2 ester bond. The reaction was examined for simultaneous 18O incorporation into the substrate. No exchange was found, suggesting that the hydrolytic step is not followed by a higher energy transition state and that it or a step before it appears to be rate-limiting. Previous experiments on phosphatidylethanolamine activation indicate that kcat is altered but that the km remains the same upon activation, suggesting that the binding steps occurring before the hydrolytic step are not affected. This strongly suggests that the hydrolytic step is in fact the rate-limiting step under these conditions. The 13C, 18O NMR technique should be generally applicable to mechanistic questions of this type.

Immunocytochemical localization of pancreatic carboxylic ester hydrolase in human paneth cells

The protein-A gold method using specific rabbit sera directed against pure human pancreatic chymotrypsinogen and carboxylic ester hydrolase was applied to locate these (pro)enzymes in human pancreatic acinar cells and intestinal Paneth cells. Quantitative evaluation of the labelling indicated that both (pro)enzymes are present in pancreatic acinar secretory granules. In Paneth cell secretory granules, only carboxylic ester hydrolase was present in significant amounts, although the labelling for this enzyme was less intense than that observed in pancreatic zymogen granules. The results obtained support the view that Paneth cells represent a "diffuse exocrine gland" scattered along the intestine, whose role is either to act as a substitute in the event of a deficient pancreas or to regulate the intestinal flora.

Immobilized phospholipase A2 from cobra venom. Prevention of substrate interfacial and activator effects

The activation of cobra venom phospholipase A2 by activators (containing phosphorylcholine moieties) appears to depend upon the aggregation state of the enzyme, and the presence of a lipid-water interface. The characteristics of this activation were studied by comparing the behavior of the enzyme immobilized on an agarose gel to that of the soluble enzyme. The immobilized enzyme displays only a few per cent of the soluble enzyme activity toward micellar dipalmitoyl-phosphatidylcholine (PC). However, the relative loss of activity is much less with micellar dipalmitoylphosphatidylethanolamine or soluble diheptanoyl-PC. The affinity for Ca2+ is increased about 10-fold by immobilization while the apparent pKa of the enzyme is decreased by 0.5-0.8 pH units. Activation energies are similar for the two enzyme forms and are independent of the physical state of the substrate used. Catalytic constants of the enzyme toward monomeric PC are not changed by immobilization. Yet, activators of the soluble enzyme have negligible effect on the immobilized enzyme, either in the presence or absence of an interface. Monomeric activators promote the binding of the soluble enzyme to the immobilized form. Apparently, immobilization mainly produces monomerically constrained enzyme which cannot be activated under any condition, whereas normally, activators in the presence of lipid-water interfaces induce the formation of enzyme dimers or possibly higher order aggregates.

Pancreatic stone protein. II. Implication in stone formation during the course of chronic calcifying pancreatitis

Pancreatic stone protein, a novel protein isolated from pancreatic stones of patients suffering from chronic calcifying pancreatitis and secreted in normal human pancreatic juice, was measured by radial immunodiffusion in pure pancreatic juice. Patients with chronic calcifying pancreatitis of different etiologies had significantly lower levels of pancreatic stone protein when compared with other pancreatic diseases and controls. Pancreatic stone protein suppresses in vitro calcium carbonate precipitation and therefore stabilizes normally supersaturated pancreatic juice. The decreased pancreatic stone protein levels observed could be a key factor in the growth of calcium carbonate crystals and stone development during the course of chronic calcifying pancreatitis.

Cobra venom phospholipase A2 inhibition by manoalide. A novel type of phospholipase inhibitor

Manoalide, an unusual nonsteroidal sesterterpenoid recently isolated from sponge, antagonizes phorbol-induced inflammation but not that induced by arachidonic acid, suggesting that manoalide acts prior to the cyclooxygenase step in prostaglandin synthesis, possibly by inhibiting phospholipase A2. We have now studied the inhibitory effect of manoalide on a homogeneous preparation of phospholipase A2 from cobra venom. For a given concentration of manoalide, the inhibition of phospholipase A2 activity toward dipalmitoylphosphatidylcholine/Triton X-100 mixed micelles is time-dependent and plateaus at about 85% inhibition of the initial velocity even after extensive preincubation. Metal ions (Ca2+, Ba2+, Mn2+) increase the inhibition, while lysophosphatidylcholine and substrate micelles protect. Increasing manoalide concentration shows increasing inhibition of the initial velocity until a plateau is reached, giving a typical saturation curve with a linear double-reciprocal plot. Under typical conditions (20-min preincubation, 40 degrees C, pH 7.1), 50% inhibition is achieved at a manoalide concentration of about 2 X 10(-6) M. The data indicate that manoalide is a potent inhibitor of the cobra venom phospholipase A2. Manoalide is now shown to react irreversibly with lysine residues in the enzyme. Surprisingly, the cobra venom phospholipase normally acts poorly on phosphatidylethanolamine as substrate, but after reaction with manoalide, the enzyme is somewhat more active toward this substrate rather than being inhibited. This suggests that a lysine residue may be important in understanding the substrate specificity of phospholipase A2.

The molecular characteristics of a human pancreatic acidic phosphoprotein that inhibits calcium carbonate crystal growth

A CaCO3-crystal-growth inhibitor was isolated from human pancreatic stones by using EDTA demineralization, followed by DEAE-Trisacryl chromatography. The isolated inhibitor was found to be a phosphoglycoprotein with Mr 14017 and having an unusual chemical composition. It is characterized by a high (42%) acidic amino acid content, but lacks methionine and gamma-carboxyglutamic acid. The protein contains 2.65 mol of P/mol of protein, as phosphoserine (2 mol) and phosphothreonine (0.5 mol). Isoelectric focusing of the protein yields one major band corresponding to an isoelectric point of 4.2. Immunochemical quantification of the crystal-growth inhibitor in pure pancreatic juice reveals that it constitutes 14% of the normal exocrine secretion. Our findings demonstrate that this is a novel secretory protein, which has no enzymic activity and which maintains pancreatic juice in a supersaturated state with respect to CaCO3.

Implication of a tyrosine residue in the unspecific bile salt binding site of human pancreatic carboxylic ester hydrolase

Tyrosine residues of the human pancreatic carboxylic-ester hydrolase (EC 3.1.1.1) (also referred to as cholesterol-ester hydrolase, EC 3.1.1.13) were nitrated in the ortho-position by the use of tetranitromethane. The specificity of the reaction has been verified and the inhibition observed was shown to be unrelated to the weak polymerization of the protein. Among the 27 tyrosines present in the enzyme, seven or eight were nitrated but only one residue, with a pK of 8.3, seems to be responsible for the loss of activity. This decrease in enzyme activity appears only in assays which were performed in the presence of bile salts, suggesting that of the two bile salt binding sites postulated on the enzyme, only one, referred to the as the 'unspecific site' (Lombardo, D. and Guy, O. (1980) Biochim. Act 611, 147-155), was modified. This is in agreement with the similar loss of enzyme activity observed on emulsified and soluble substrate. The most important result is the difference observed in experiments of the protective effects of bile salts. The protection with sodium taurodeoxycholate is independent of its critical micellar concentration, showing that monomers protect this site, whereas the protection observed in experiments with sodium cholate appears only for supramicellar concentrations of bile salt. Since this latter bile salt promotes the dimerization of the enzyme, we can conclude that a premicellar bile salt binding site (protected by monomers) is transformed in a functional micellar binding site (protected by micelles). This conformational transformation seems to be consecutive to the dimerization, as has been recently proposed.

On the probable involvement of arginine residues in the bile-salt-binding site of human pancreatic carboxylic ester hydrolase

Modification of arginine residues with 2,3-butanedione inhibits the carboxylic-ester hydrolase activity on soluble and emulsified substrates when assayed with bile salts. The alpha-dicarbonyl reagent modifies seven of the nineteen arginine residues present per enzyme molecule. Nevertheless the inactivation with butanedione is greatly diminished when the protein is in the presence of negatively charged micellar bile salt. In these conditions we observe the protection of one arginine residue by sodium taurodeoxycholate and of two arginine residues by sodium cholate. This suggests that the carboxylic-ester hydrolase from human pancreatic juice contains at least two arginine residues essential for the activation by bile salts. All our data confirm the presence of two bile-salt-binding sites on the enzyme in which one arginine per site is involved and plays the general role of an anionic binding site. This study provides evidence that arginine residues may play an essential role in the interaction between bile salts and protein.

Catalytic properties of modified human pancreatic carboxylic-ester hydrolase

Human pancreatic carboxylic-ester hydrolase (EC 3.1.1.1) modified by specific reagents (diisopropyl phosphorofluoridate, diethyl p-nitrophenyl phosphate, Woodward's K reagent and ethoxyformic anhydride) was studied for its activity. The three residues probably implicated in the active site acting on soluble substrate are shown to be essential for the activity on emulsified substrates such as tributyrin or cholesterol esters solubilized by bile salts (hydrolyzing and synthetizing activities). The modified enzyme is still able to bind to interfaces. Nevertheless, one supplementary carboxylic acid group is responsible for the stability of the enzyme bound to interfaces.

Modification of the essential amino acids of human pancreatic carboxylic-ester hydrolase

Chemical modification of human pancreatic carboxylic-ester hydrolase (EC 3.1.1.1) were performed using organophosphorus compounds, ethoxyformic anhydride and Woodward's K reagent. It has been shown that: (1) the inhibition of the enzyme activity by organophosphorus compounds is due to the phosphorylation of only one alcohol residue, probably a serine residue which may represent the acylable group of the enzyme: (2) 35-36 free carboxyl groups are modified by Woodward's K reagent but only one is responsible for the loss of enzyme activity. This carboxyl group has a pKa of 5.2.: (3) carbethoxylation of histidine residues leads to the inhibition of the enzyme activity. All nine histidine residues are reactive but only one is essential for activity. Taking into account the probable formation of an acyl-enzyme intermediate (Lombardo, D. and Guy, O. (1981) Biochim. Biophys. Acta 657, 425-437) during substrate hydrolysis and the present data we discuss a possible mechanism for carboxylic-ester hydrolase catalysis, a mechanism similar to that described for chymotrypsin.

Structure and conformation of human pancreatic carboxyl-ester hydrolase

Human pancreatic carboxyl-ester hydrolase is a glycoprotein with a molecular weight of 100 000 and a high content in carbohydrate, 20%. Sedimentation studies indicate that the molecule resembles an ellipsoid. The results of hydrodynamic and vacuum-ultraviolet circular dichroism investigation allow one to propose a model of the carboxyl-ester hydrolase three-dimensional structure. The enzyme belongs to the "all beta" class of proteins; about 54-60% of its residues are in beta-sheets and in beta-turns, most probably forming the surface of an ellipsoid. A similarity with prealbumin structure is proposed and a comparison with structure of other pancreatic enzymes is presented.

Binding of human pancreatic carboxylic ester hydrolase to lipid interfaces

Human pancreatic carboxylic ester hydrolase (EC 3.1.1.1), usually characterized by its activity on water-soluble substrates, is shown to catalyze reactions taking place at a lipid/water interface. The inhibition of tributyrin hydrolysis by 1-alcohols follows the pattern of a Langmuir adsorption isotherm. Experiments performed with siliconized glass beads show that human pancreatic carboxylic ester hydrolase is adsorbed on this artificial (or substitute) interface with a dissociation constant for the enzyme-glass beads complex equal to 1.5 . 10(-8) M. The average molecular area at saturation is 4375 A2. Tripropionin hydrolysis is increased by the presence of glass beads. These results are strong arguments in favor of the interfacial activity of pancreatic carboxylic ester hydrolase. The activation of the enzyme bound to the interface is very weak. Bile salts do not prevent the adsorption of carboxylic ester hydrolase on siliconized glass beads and increase strongly the hydrolysis rate of emulsified tributyrin.

Effect of alcohols on the hydrolysis catalyzed by human pancreatic carboxylic-ester hydrolase

Transfer reactions catalyzed by human pancreatic carboxylic-ester hydrolase (EC 3.1.1.1) were studied in the presence of methanol and butanol as nucleophiles. The addition of alcohols produced an increase in the total rate of 4-nitrophenyl acetate and n-propylthiol acetate disappearance and a concomitant slow decrease of the hydrolysis rate. These results indicate a competitive partitioning of an acyl-enzyme intermediate between water and nucleophile. Moreover, a strong inhibition of the rates of hydrolysis of methyl butyrate and triacetin by nucleophiles is in agreement with a rate-limiting acylation step. The kinetic data and a trans-ester characterization argue in favor of the formation of an acyl-enzyme intermediate and a two-step reaction mechanism, acylation and deacylation both being rate-limiting. The experiments performed with 4-nitrophenyl acetate show the existence of a nucleophile binding site.

Esterification of cholesterol and lipid-soluble vitamins by human pancreatic carboxyl ester hydrolase

Human pancreatic carboxyl ester hydrolase is shown to catalyse the esterification of cholesterol and lipid-soluble vitamins A, E and D3 with oleic acid. The acitivity requires the presence of bile salts, and the trihydroxylated or the 3 alpha, 7 alpha dihydroxylated bile salts are better activators than the 3 alpha, 12 alpha dihydroxylated bile salts. The hydrolyzing and synthetizing activities of human pancreatic carboxyl ester hydrolase are separated by a large pH range since the synthesis of cholesterol esters is optimal at pH 5.25 and the hydrolysis of cholesterol and vitamin E esters is optimal at pH 8.0. From the comparison of the catalytic constants determined for the hydrolyzing and synthetizing activities and from the pH dependence of the two activities, it appears that human carboxyl ester hydrolase plays an important part in the intestinal lumen. The role of the enzyme in the esterification of cholesterol and lipid-soluble vitamins is questionable.

Studies on the substrate specificity of a carboxyl ester hydrolase from human pancreatic juice. I. Action on carboxyl esters, glycerides and phospholipids

Purified carboxyl ester hydrolase (carboxylic-ester hydrolase, EC 3.1.1.1) from human pancreatic juice was found to hydrolyze triacetin, methyl butyrate and glycerides solubilized by bile salts. It has no activity on substrate presented as emulsoin or monomolecular films. The human enzyme was found to deacylate phospholipids and lysophospholipids at different rates. The hydrolysis of short-chain phosphatidylcholines was dependent of substrate solubility and dioctanoyl phosphatidylcholine was deacylated with the highest rate. Long-chain phosphatidylcholines and lysophosphatidylcholines present in microsomal membranes were deacylated with very low rates, only lysophosphatidylcholine deacylation was faster. Evidence is presented that human carboxyl ester hydrolase is the lyophosphatidyl-choline-hydrolyzing enzyme corresponding to bovine lysophospholipase. Bile salts play an important part on the activity of human carboxyl ester hydrolase, in addition to the role of detergent that they have on insoluble substrates.

Studies on the substrate specificity of a carboxyl ester hydrolase from human pancreatic juice. II. Action on cholesterol esters and lipid-soluble vitamin esters

Evidence is presented that human carboxyl ester hydrolase (carboxylic-ester hydrolase, EC 3.1.1.1) is able to hydrolyze cholesterol esters and lipid-soluble vitamins A, D-3 and E esters. Those activities require the presence of bile salts and the 3 alpha, 7 alpha-dihydroxylated bile salts have been found the most efficient activators. The results presented in this paper and in the preceding one suggest the existence of two sites of bile salts recognition. One site, specific of the 3 alpha, 7 alpha-hydroxyl group of cholanic acid would induce dimerization and activation of the enzyme. The other site, unspecific towards bile salts hydroxylation would be located at the active center and would be implicated in substrate recognition.

Purification and characterization of a carboxyl ester hydrolase from human pancreatic juice

A carboxyl ester hydrolase has been purified 20-fold from human pancreatic juice. It is a glycoprotein with a molecular weight of 100 000. It contains 9% neutral and amino carbohydrates and the amino acid composition is characterized by a high content of proline residue (12.7%). The enzyme catalyzes the hydrolysis of p-nitrophenylacetate and the activity increases in the presence of biliary salts; V is not modified but Km is decreased 10 times by addition of biliary salts. The enzyme migrates on Sephadex G-200 as a protein with a molecular weight of 300 000. This behaviour does not seem to be due to a polymerization but to a peculiar configuration of the enzyme.

Two human trypsinogens. Purification, molecular properties, and N-terminal sequences

The two human trypsinogens have been isolated from human pancreatic juice in a sufficient amount to study molecular and structural properties. The purification procedure included filtration on Sephadex G-100 followed by ion-exchange chromatography on DEAE-cellulose. The two trypsinogens represent 19% of total proteins of pancreatic juice. Trypsinogen 1, the major form, is present in a quantity twice that of trypsinogen 2, which is the most anionic protein in human pancreatic juice. The two proteins have partial immunological identity, close molecular weights (23 438 and 25 006 for trypsinogens 1 and 2, respectively) and similar amino acid compositions. The N-terminal sequences are the same for the first 9 residues: Ala-Pro-Phe-Asp4-Lys-Ile. The two proteins differ in the activation peptides released during the transformation to trypsins. Trypsinogen 2 liberates one octapeptide Ala-Pro-Phe-Asp4-Lys while trypsinogen 1 liberates two peptides, the same octapeptide and the pentapeptide (Asp)4-Lys.

[The medico-social problem of rheumatic valve disease in Sicily]

The incidence of rheumatism and rheumatic valvulopathy in Sicily is assessed and the sites most commonly involved in the first and second attacks described. The medical aspects of te question are examined from several points of view: prophylaxis of sites, medical treatment personal and ambient hygiene, gradual defectiveness of the pump, associated diseases, etc. The concept of invalidity is viewed in terms of direct and associated anatomical damage and frank and potential invalidity (absolute or relative), the weight or assistance attributable to the family and the incidence of the local social environment in the question of finding work, etc. The basic criteria for surgery are noted. Care must be taken to preserve the few remaining structures. Mortality is still high and the incidence of heart disease is higher among rheumatic Sicilian children. Not enough is known about overcrowding, the schools attended by the poor, and the higher incidence in low-income classes. Failure to affront some of these features, determined as much by action (or its postponement) by government as by income, results in meaningless medicine, divorced from social reform and true the scientific spirit, a cover for special interests and a demonstration of profit factors wherein the commercialising relationship is increasingly evident.

[Necrosis of the pouch due to nontraumatic rupture of the pile during permanent endocardial electrostimulation]

Necrosis of the pouch containing the generator, due to non-traumatic breakage of the batteries, was observed in a patient with a permanent pacemaker, followed by rapid ingravescence. The cause of this complication is discussed. Chemical inflammation was noted soon after the pacemaker ceased to function. Initially this was similar to the not uncommon bacterial inflammation noted in such patients. Here, of course, the pacemaker usually continues to work, and its replacement is optional, whereas in the reported case is an emergency matter. In situations where tissue distress in the pouch is accompanied by inflammation, therefore, thought should be given to the possibility that, even if the batteries are still working, the cause may be chemical or electrochemical rather than septic, and than sudden breakdown of the generator may be expected.

[Permanent endocardiac electrostimulation. Considerations on 511 implantations and reimplantations in 7 years of practice]

Permanent pacemakers were implanted and reimplanted in a total of 511 patients (mostly men) during a period of about 7 yr. Mean age was 67.9 yr. The cephalic route was used in nearly every case, with subclavicular implantation of the generator. Mean hospital stay was 7.6 days. Ventricular inhibition pacemakers were used in over 84% and fixed-frequency models in 7%. Mean pacemaker life was 24.1 months, with longer periods in the last months of the period of observation. The evaluation of battery run-down and recent and long-term complications is discussed, together with a particular type of decubitus of electrolytic origin. Hospital mortality was 2%. Survival was 91% at 1 yr and 54% at 6 yr. Emphasis is placed on the fact that subjects continue to be heart patients. Their well-being depends on psychological and general medical care, together with help from their, families and society, quite apart from cardiological attention.