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Biomedical subjects

K R Norum

Publications and source records attributed to K R Norum.

At least 145 records · Page 8Linked to original sources
PubMed1977

Uptake and degradation of cholesterol ester-labelled rat plasma lipoproteins in purified rat hepatocytes and nonparenchymal liver cells.

1. A new method for isolation and purification of rat liver hepatocytes and nonparenchymal cells by differential centrifugation is described. 2. Cholesterol ester-labelled lipoproteins (prepared by the action of lecithin: cholesterol acyltransferase) intravenously injected were taken up by hepatocytes and nonparenchymal cells. 3. Hepatocytes and nonparenchymal cells in suspension were able to take up and hydrolyse the cholesterol ester portion of lipoproteins. 4. Uptake of cholesterol ester labelled whole rat plasma and high density lipoproteins (HDL) increased with increasing concentrations until a distinct saturation level was reached in hepatocytes. In nonparenchymal cells there was no saturation of lipoprotein uptake. 5. Concanavalin A inhibited cholesterol ester-labelled lipoprotein uptake in hepatocytes, indicating that the uptake at least partially depends on carbohydrate sites on the cell surface. The uptake in nonparenchymal cells was unaffected of concanavalin A. 6. The specific activity of the acid cholesterol ester hydrolase was the same in homogenates from hepatocytes and nonparenchymal cells while acyl-CoA: cholesterol acyltransferase was found almost exclusively in hepatocytes.

Acid Phosphatase↗
PubMed1977

The effect of D-galactosamine on LCAT secretion and ultrastructure of isolated rat hepatocytes.

The effect of D-galactosamine on secretory activity and morphology of isolated rat hepatocytes was investigated: Galactosamine was found to reduce the secretion of lipoproteins (as indicated by the release of free cholesterol and triacylglycerol) as well as the secretion of lecithin: cholesterol acyltransferase (LCAT) and [14C]-labelled proteins from the isolated cells. The secretion of LCAT was inhibited much more than that of the other secretory products studied. Transmission electron microscopy revealed that galactosamine induced morphological changes in RER, mitochondria and nucleoli. The most striking feature of galactosamine-treated hepatocytes, however, was the appearance of swollen lysosomes. Some of these organelles measured up to 3 mumicrometer in diameter. Uridine did not abolish the effect of galactoosamine upon the secretory activity of hepatocytes. The most conspicuous ultrastructural feature in cells that had been incubated with both uridine and galactosamine was the appearance of large amounts of glycogen. The possibility that galactosamine inhibits glycogenolysis is discussed. The rather selective effect of galactosamine on LCAT secretion suggests the use of this compound for the study of the interrelationship between LCAT and lipoprotein secretion.

Animals↗
PubMed1977

Coenzyme-A-dependent esterification of cholesterol in intestinal mucosa from guinea-pig. Influence of diet on the enzyme activity.

Guinea-pig intestinal mucosa contains a microsomal enzyme which catalyses the esterification of cholesterol. The enzyme is CoA-dependent and probably an acyl-CoA-cholesterol acyltransferase (ACAT) (E.C. 2.3.1.26). The apparent Km for the CoA in the combined enzyme reaction is 3.3 x 10(-5)M. The specific activity of cholesterol esterification is about five times higher in young suckling animals than in ordinary fed adult animals. Feeding fat and fat/cholesterol diets increases the activity two- to five-fold. Concomitantly the fat/cholesterol fed animals get a marked accumulation of free and esterified cholesterol in mucosal cells.

Acyltransferases↗
PubMed1977

The lecithin-cholesterol acyl transferase activity of rat intestinal lymph.

The lecithin-cholesterol acyl transferase (LCAT) activity in rat mesenteric lymph was examined as a possible source of chylomicron cholesteryl ester. Lymph activity was only 2-3% of rat serum activity. Removal of d less than 1.006 lipoproteins increased lymph LCAT activity, but only to 6-8% of that of serum. Relative to total cholesterol in the d greater than 1.08 g/ml fractions, lymph LCAT activity in lymph from fasting rats was less than serum, but in lymph from nonfasting rats the ratio LCAT/HDL-cholesterol reached levels greater than serum, suggesting a contribution of enzyme from the gut. Both LCAT activity and HDL concentration in mesenteric lymph increased during feeding. Subfractions of lymph that inhibited serum LCAT were: chylomicrons, VLDL, chylomicron lipid, VLDL apoprotein, and HDL apoprotein. In the rat, the low LCAT activity of mesenteric lymph was in part due to the low enzyme concentration present, and the activity was apparently lowered further by lipid-rich lipoproteins that inhibited the reaction. Enzyme inhibition due to the apoprotein fractions of lipoproteins is probably minor in the rat in vivo.

Acyltransferases↗
PubMed1976

Secretion of lecithin: cholesterol acyltransferase from isolated rat hepatocytes.

1. Lecithin:cholesterol acyltransferase is secreted from isolated rat heptocytes. 2. The secretion is stimulated when serum is added to the incubation medium. 3. Optimal conditions for secretion are: 5-10(6) hepatocytes per ml, 5 h incubation, pH 7.3-7.4 and 25% serum in the incubation medium. 4. Concomitantly with the secretion of lecithin:cholesterol acyltransferase there is a secretion of unesterified cholesterol and triacylglycerol. 5. Colchicine or cycloheximide in the incubation medium inhibits secretion of lecithin:cholesterol acyltransferase.

Acyltransferases↗
PubMed1976

Affinity chromatography of 3 alpha-hydroxysteroid dehydrogenase from Pseudomonas testosteroni. Use of N,N-dimethylformamide to prevent hydrophobic interactions between the enzyme and the ligand.

1. The 3alpha-hydroxysteroid: NAD+-oxidoreductase (EC 1.1.1.50) from Pseudomonas testosteroni (ATCC 11996) has been purified by affinity chromatography on Sepharose 4B using glycocholic acid as ligand covalently bound through its carboxyl group to the ethylenediamine spacer. 2. The attachment of the enzyme to the substrate-containing matrix is greatly enhanced by the presence of NAD+ suggesting that this enzyme has a compulsory ordered mechanism where NAD+ binds to the enzyme before the steroid. 3. A NAD+-independent interaction between the enzyme and the ligand was also found. This interaction was mainly hydrophobic and interfered with the NAD+-dependent binding. The NAD+-independent interaction was reduced by N,N-dimethylformamide. 4. By using the affinity column in the presence of 10% N,N-dimethylformamide, highly purified enzyme, as judged from polyacrylamide gel electrophoresis, could be obtained in one step from crude bacterial extracts.

Chromatography, Affinity↗
PubMed1976

Newly synthesized hepatic cholesterol as precursor for cholesterol and bile acids in rat bile.

Adult, male rats were given simultaneously 3H-mevalonate and 14C-cholesterol on autologous lipoproteins intravenously in barbital anaesthesia. The specific radioactivities of sterols in bile, liver and serum were determined. Newly synthesized hepatic cholesterol was a better substrate for cholic and chenodeoxycholic acid than was cholesterol reaching the liver via plasma lipoproteins. The cholesterol secreted into bile was derived from a pool of liver cholesterol which was in close contact with newly synthesized cholesterol. Specific radioactivity of chenodeoxycholate in bile was higher than that of cholate in bile, both when newly made radioactive cholesterol and when radioactive cholesterol on plasma lipoproteins was the precursor for the labelled bile acids.

Animals↗
PubMed1976

Coenzyme-A-dependent esterification of cholesterol in rat intestinal mucosa.

Rat intestinal mucosa contains an enzyme which catalyses the esterification of cholesterol. The enzyme is CoA-dependent and probably an acyl-CoA: cholesterol acyltransferase (ACAT) (E.C.2.3.1.26). Maximal activity in vitro is obtained when long chain acylcarnitines, CoA and carnitine palmityltransferase are used as an acyl-CoA generating system. The enzyme is localized in the microsomal fraction, has a pH optimum between 6.4-7.2, and oleate is the preferred acyl group. The activity of the enzyme is highest in the proximal jejunum, and has a capacity that can account for all cholesteryl esters found in intestinal rat lymph.

Acetyl Coenzyme A↗
PubMed1975

Cholesterol esterification and lipids in plasma and liver from newborn and young guinea pigs raised on milk and non-milk diet.

Plasma lecithin:cholesterol acyltransfer (LCAT), liver acyl-CoA:cholesterol acyltransfer (ACAT) and plasma and liver lipids were examined in newborn and young guinea pigs fed ordinary or a non-milk diet. LCAT in newborns was about 70% of the adult value, increased the first 3 days to values about three times the adult value, and decreased during the next 3 weeks to about adult value. Plasma lipids varied in a similar way. Liver ACAT in newborns was considerably higher than in adults. In young animals on non-milk diet the LCAT and ACAT were lower than in normally fed animals. LCAT was positively correlated to free cholesterol in plasma.

Acyltransferases↗
PubMed1975

Effect of lipid emulsions on the plasma lecithin: cholesterol acyltransfer in guinea pigs.

Addition of triglyceride/phospholipid emulsion to adult guinea pig plasma more than doubled the cholesteryl ester (CE) production. Plasma from newborn guinea pigs was stimulated to a lower degree. The increase in CE production was dependant on the type and amount of phospholipids in the lipid emulsions. Egg phospholipids stimulated the cholesterol esterification while partially hydrogenated soy phospholipids (with high content of saturated fatty acids) inhibited the reaction. The stimulation of CE formation was probably due to transfer of phosphatidyl choline (PC) from the emulsion to the high density lipoproteins since the stimulation was: (a) dependant on a preincubation time, (b) less pronounced in newborn animals with high plasma PC levels, and (c) detected in plasma fractions from which the lipid emulsion had been removed.

Acyltransferases↗
PubMed1975

[School meals].

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Feeding Behavior↗
PubMed1975

Plasma lipoproteins in familial lecithin: cholesterol acyltransferase deficiency: effects of dietary manipulation.

To study the metabolism of the abnormal plasma lipoproteins in familial lecithin:cholesterol acyltransferase deficiency we performed five dietary experiments designed to perturb their distribution and composition. Four patients with the disease were given successive diets that differed in triglyceride, carbohydrate, or cholestrol content, and after each dietary period the lipoproteins were analyzed by combinations of preparative and analytical ultracentrifugation, gel filtration, chromatography, and disc gel electrophorsis. Lowering the intake of long chain, dietary triglyceride descreased the concentrations of the large very low density lipoproteins, the large and intermediate low density lipoproteins, and the small high density lipoproteins by as much ad 79 %, but either increased or did not change the concentrations of the small very low and low density lipoproteins. Re-adding long chain triglycerdine to the diet generally reversed these effects, but increasing the dietary cholesterol without lowering the dietary triglyceride only decreased the concentration of plasma cholesteryl ester. We conclude that the concentrations of the large very low and low sensity lipoproteins, the intermediate-sized low density lipoproteins, and the small high density lipoproteins are related to the absorption and subsequent transport of long chain dietary fatty acids. Since these lipoproteins are rich in unesterified cholesterol and lecithin, two polar lipids that form a substantial part of the surfaces of chylomicrons, components of chylomicron surfaces may accumulate in the patient's plasma following enzymic removal of chylomicron triglyceride and contribute to several of the abnormal lipoproteins.

Acyltransferases↗
PubMed1975

Plasma lipoproteins in familial lecithin: cholesterol acyltransferase deficiency: effects of incubation with lecithin: cholesterol acyltransferase in vitro.

To study the effect of lecithin: cholesterol acyltransferase (LCAT) on the plasma lipoproteins of patients with familial LCAT deficiency, whole plasma or the lipoprotein fraction of d smaller than 1.006 g/ml (VLDL) was incubated in the presence of LCAT and subsequently examined by chemical, physical, and immunological techniques. The following occured upon incubating either hyperlipemic or nonlipemic plasma: The concentrations of polar lipids decreased, particulary in the large molecular weight lipoprotein subfraction of d 1.019-1.063 g/ml (LDL2) and in the lipoprotein fraction of 1.06301.25 g/ml (HDL). The concentration of cholesteryl ester (CE) increased, particularly in the VLDL and in the lipoprotein fractions of d 1.006-1.019 g/ml (LDL1) and LDL2. The concentration of arginine-rich apolipoprotein decreased in the HDL and increased in the VLDL and LDL1. The concentrations of the C-apoliproteins appeared to change in the opposite direction. The concentration of apolipoprotein B in the LDL increased concomitantly with an increase in the concentration and flotation rsate of the small LDL2. The concentration apolipoprotein A-I in the HDL increased; and a major component in the HDL fraction became identical in apperance to normal HDL. Upon incubating a patient's isolated VLDL in the presence of LCAT, lipoproteins with properties similar to normal LDL2 were formed. These experiments show that the LCAT reaction can alter the apolipoprotein content and physical properties as well as the lipid content of the patient's lipoproteins.

Acyltransferases↗