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Biomedical subjects

B Borgström

Publications and source records attributed to B Borgström.

At least 55 records · Page 3Linked to original sources
PubMed1982

Product activation of pancreatic lipase. Lipolytic enzymes as probes for lipid/water interfaces.

During the action of pancreatic lipase and colipase on racemic 1,2-didodecanoylglycerol monolayers in the absence of bile salts, biphasic kinetics was observed under conditions of high lipid packing. Similar kinetics has earlier been reported using phospholipid-emulsified triolein droplets (Borgström, B. (1980) Gastroenterology 78, 954-962). These kinetics are characterized by a lag time tau d, dependent on products accumulation at the substrate/water interface. This lag time is differentiated from the previously described enzyme concentration independent lag time tau i in systems of low lipid packing (Verger, R., Mieras, M. C. E., and de Haas, G. H. (1973) J. Biol. Chem. 248, 4023-4034). Both tau i and tau d reflect a rate-limiting step due to the slow enzyme penetration into the substrate interface. The variation of tau d under different conditions (change in pH and concentration of Ca2+, enzyme, bovine serum albumin, and lipolytic products) lead us to propose a model for the product activation during lipolysis. We will discuss the use of the pancreatic lipase-colipase system to probe the lipid packing of emulsified triglyceride particles and lipoproteins using tau d as a reference value.

Animals↗
PubMed1982

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.

Animals↗
PubMed1982

Isolated co-lipase deficiency in two brothers.

Two normally developed Assyrian brothers with isolated pancreatic co-lipase deficiency are described. They presented at the age of 5-6 years with loose stools. They had steatorrhoea, and analysis of exocrine pancreatic enzymes in the small intestine showed co-lipase deficiency, while amylase, chymotrypsin, trypsin and lipase were normal. Intraduodenal infusion of purified co-lipase improved fat digestion measured by the triolein breath test. Their steatorrhoea diminished on treatment with enteric-coated pancreatic enzymes.

Bile Acids and Salts↗
PubMed1982

Hydrolysis of milk fat globules by pancreatic lipase. Role of colipase, phospholipase A2, and bile salts.

Human milk fat globules require colipase to be hydrolyzed by pancreatic lipase in the presence of bile salts. This is contrary to a recent report in this Journal (J. Clin. Invest. 67: 1748-1752.) according to which inhibition of lipase by bile salt could be overcome by the addition of colipase or phospholipase A2. This latter finding is shown to be due to contamination of commercially available pancreatic phospholipase A2 by colipase.

Animals↗
PubMed1981

Aqueous lipid phases of relevance to intestinal fat digestion and absorption.

The phase behavior of monoglyceride/water systems, with oleic and linoleic acid as the dominating fatty acid residues, was investigated. Increased solubilization of triglycerides (oil) or oleic acid in the cubic liquid-crystalline phase formed by monoglyceride and water resulted in the formation of a reversed hexagonal liquid-crystalline phase followed by an L2-phase. The liquid-crystalline phases have different dispersion properties compared to each other in dilute micellar bile salt solutions. The cubic phase is found to be easily dispersed. The relevance of aqueous lipid phases other than micellar is discussed in relation to intestinal lipid digestion and absorption.

Bile Acids and Salts↗
PubMed1980

Importance of phospholipids, pancreatic phospholipase A2, and fatty acid for the digestion of dietary fat: in vitro experiments with the porcine enzymes.

Long chain triglycerides emulsified with phospholipid are not directly available for hydrolysis by pancreatic lipase in vitro even in the presence of bile salts and colipase. The inhibition can be overcome by pancreatic phospholipase A2. There is a limited hydrolysis of the phospholipid during this period. The inhibition is explained by the finding that lipase does not bind to triglyceride emulsified by phospholipid but remains in the aqueous phase. A limited hydrolysis of the phospholipid by phospholipase A2 results in the binding of lipase to the substrate interface and a rapid rate of hydrolysis of the triglyceride. With time the inhibition of lipase activity can also be overcome by pancreatic lipase. A lag phase is seen before the accelerated hydrolysis of triglyceride reaches a high rate. The length of the lag phase is dependent on factors such as lipase and colipase concentration, pH, Ca++, and concentration of bile salt. During the lag phase no significant hydrolysis of phospholipid occurs. The primary factor is the binding of colipase to the substrate interface. Fatty acid present in the oil phase or produced from it by a limited hydrolysis of phospholipid by phospholipase A2 or triglyceride by lipase, changes the properties of the interface so that colipase can bind and thereby lipase via its binding to colipase. The milieu of small intestinal content favors the concerted action of several factors to make dietary triglyceride available for an effective hydrolysis by pancreatic lipase.

Animals↗
PubMed1979

High-resolution proton magnetic resonance study of porcine colipase and its interactions with taurodeoxycholate.

A high-resolution 270-MHz proton NMR study of procine colipase I has been performed, and the resonances in the aromatic region of the spectrum have been assigned to amino acid residues by pH titration and decoupling experiments. The apparent pKa values of the three tyrosines were calculated to be 10.2, 10.3, and 11.8 with one of the tyrosines having properties of a "buried" residue. A tentative assignment to the amino acid residues in the primary seuqence of colipase will be discussed. The effects of taurodeoxycholate (TDC) and a positively charged deoxycholate derivative on the aromatic region of the colipase NMR spectrum indicate that all tyrosines and one histidine are affected by the bile-salt binding, suggesting that the TDC molecules bind near these residues to a hydrophobic region on colipase. Measurements and calculations on the line width of the C(18) methyl group resonance suggest that the line-width increase of this resonance upon interaction of TDC with colipase to a large extent can be explained as due to the slower tumbling of the TDC molecules bound to colipase.

Amino Acid Sequence↗
PubMed1979

Purification and characterization of human pancreatic colipase.

Two colipases, named colipase I and colipase II, have been isolated from extracts of human pancreatic gland. The two proteins can be separated by ion-exchange chromatography, isoelectric focusing and slab technique gel electrophoresis. The result of this study indicates that the two colipases, both of which are glycoproteins, have identical amino acid compositions. The pI values were found to be 6.1 for colipase I and 5.8 for colipase II. The different colipases have also been found in human pancreatic juice. The N-terminal amino acid was glycine for both colipase I (gland) and colipase II (juice). Only minor differences were found between the colipases isolated from gland and juice, and colipase I from gland alone was examined in detail.

Amino Acid Sequence↗
PubMed1978

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.

Animals↗