PubMed Health⌕ Search

Biomedical subjects

R Got

Publications and source records attributed to R Got.

At least 55 records · Page 3Linked to original sources
PubMed1980

[The presence of glycosyltransferases on chromatin acceptors in monkey liver nuclear membranes (author's transl)].

Nuclei were prepared from monkey hepatocytes by centrifugation of the homogenate on a cushion of 2.3 M sucrose, during 45 min at 100000 X g. The yield was 2.2 x 10(7) nuclei per g of liver, and 70% of te homogenate DNA was recovered in these nuclei. An electron microscopic study as well as a biochemical analysis of marker enzymes showed that the nuclei are not contaminated by other subcellular fractions, especially endoplasmic reticulum. A mannosyltransferase and an N-acetylglucosaminyltransferase, working on endogenous glycoproteic acceptors, are present in the nuclei for 1.4 and 6.5% of the homogenate activities, respectively. The nuclei are hydrolysed by DNAse I. The suspension, adjusted in 1.9 M sucrose, was centrifuged for 2 h at 100000 X g, under buffer layer. Purified nuclear membranes were collected at the interface. These membranes did not contain any more endoplasmic reticulum enzyme activities, but the mannosyl and N-acetylglucosaminyltransferase activities were still present. They essentially work on an exogenous chromatin acceptor, prepared by lysis of the nuclei. The eventual role of these glycosyltransferases in the glycosylation of non-histone proteins is discussed.

Acetylglucosamine↗
PubMed1980

[Effects of basic proteins of low molecular weight on the phosphohydrolase and phosphotransferase activities of microsomal glucose-6-phosphatase in adult monkey hepatocytes (author's transl)].

The effects of histone 2A and some polycations on microsomal carbamylphosphate:D-glucose phosphotransferase and glucose-6-phosphate phosphohydrolase activities (D-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9), have been investigated. 1. Histone 2A and polycations activate the two enzymic activities. At a constant cation concentration, this activation increases with the number of cationic groups per molecule. 2. Activation by histone 2A is related to its fixation on microsomal membranes. This fixation varies with quantities of histones and pH. 3. The nature of the interactions between histones and microsomal membranes is shown to be electrostatic, probably between the cationic groups of histones and the anionic group of membranous lipids. 4. Kinetic analysis reveal that histone 2A increases the maximal reaction velocity but does not affect the apparent Michaelis constant values for the substrates. 5. The role played by the cationic groups of histone 2A on the microsomal glucose 6-phosphatase, is discussed.

Animals↗
PubMed1979

[Comparative study of microsomal enzymic activities in adult and foetal monkey hepatocytes (author's transl)].

Differential centrifugation was applied to adult and foetal liver of monkey. Obtained fractions were: F1 (800 X g); F2 (12 500 X g); F3 (200 000 X g); and cell sap. Analysis of chemical compounds of these fractions shows that: (1) adult and foetal nucleic acids levels are similar; (2) there are more proteins in adult than in foetal hepatocytes; (3) most of the glycogen is located in F3; the foetal level is twenty times higher than the adult level. Plasma membrane enzymes (5'-nucleotidase, adenylate cyclase) show a nucleomicrosomic distribution. The distribution of alkaline phosphatase is not significant. Mitochondrial enzymes (monoamine oxydase, succinate cytochrome c reductase, cytochrome oxydase) are enriched in F2 without any sedimentation in F3. There is more malate dehydrogenase liberated in cell sap during foetal liver fractionation. This indicates the foetal mitochondria are more sensitive to the homogenisation method. Lysosomal enzymes (acid phosphatase, N-acetylglucosaminidase) are enriched in F2. The same observation for N-acetylglucosaminidase as for malate dehydrogenase leads to the same conclusion for foetal lysosomes. Endoplasmic reticulum and Golgi enzymes (glucose-6-phosphatase and related phosphotransferase activity, NADPH-cytochrome c reductase and sialytransferase) are much enriched in F3. Thus this fraction F3 is pure enough to allow the observation of the modification produced on endoplasmic reticulum and Golgi apparatus during foetal and neonatal development.

Aging↗
PubMed1979

Evidence for glycosyltransferases in trout liver microsomes (Salmo gairdneri).

1. Trout (Salmo gairdneri) serum is rich in glycoproteins which are synthetized in liver. 2. An attempt to localize glycosyltransferases in hepatocytes is described, using cellular fractionation and marker enzyme determination. 3. Galactosyltransferase, mannosyltransferase, N-acetyl-glucosaminyl transferase, glucosyltransferase, sialyltransferase (on exogenous acceptor) are found in a microsomal fraction obtained by centrifugation at 117 X 10(5) g min of the post-mitochondrial supernatant. 4. Mannose is transferred to endogenous lipids and proteins.

Animals↗
PubMed1979

[Monkey liver microsomal glucose-6-phosphatase].

Kinetic studies indicate that glucose-6-phosphatase is a multifunctional enzyme. a) Phosphohydrolase activities. The mannose-6-phosphatase activity is low (Km = 8 mM, VM = 90 nmoles. min-1mg-1). The enzyme shows a strong affinity for glucose-6-phosphate (Km = 2.5 mM, VM = 220 nmoles.min-1mg-1). beta-glycerophosphate (K1 = 30 mM), D-glucose (Ki = 120 mM) are mixed type inhibitors; pyrophosphate (Ki = 2 mM) is a non competitive one. b) Phosphotransferase activities. Di and triphosphate adenylic nucleosides or phosphoenol pyruvate are not substrates. Carbamylphosphate serves as a phosphoryl donor with D-glucose as acceptor. The phosphate transfer is consisstent with a random mechanism in which the binding of one substrate increases the enzymes affinity for the second substrate. Apparent Km values for carbamyl-phosphate range from 5.2 mM (D-glucose concentration leads to infinity) to 8 mM (D-glucose concentration leads to 0). The corresponding apparent Km values for D-glucose are 59 mM (carbamyl-phosphate concentration leads to infinity) to 119 mM (carbamyl-phosphate concentration leads to 0). Maximal reaction velocity with infinite levels of both substrates is 270 nmoles.min-1.mg-1. Pyrophosphate is a poor phosphoryl donnor (Km = 55 mM with D-glucose concentration 250 mM). In addition we do not find any latency; detergents, namely sodium deoxycholate, Triton X 100 do not affect or inhibit glucose-6-phosphatase activity.

Animals↗
PubMed1979

[Presence of UTP:D-GLUCOSE-1-phosphate uridylyltransferase in liver microsomes of the eel (Conger vulgaris)].

An activity UTP : D-glucose-1-phosphate uridylyltransferase is located in the microsomal membranes of conger liver. The properties of this enzyme are studied and compared to the soluble activity. The microsomal activity is partially liberated from the membrane by freezing and thawing and by the means of a neutral detergent, Triton X-100. The enzyme is latent in the membranes and totally inhibited by phospholipase A2. This microsomal enzyme could be the last of a membranous biosynthetic pathway for UDP-glucose, as conger liver microsomes contain also a membranous glucokinase and a membranous phosphoglucomutase.

Anguilla↗
PubMed1978

[Isolation by affinity chromatography of specialized membrane fractions from cat liver microsomes].

Microsomal glucokinase is solubilized by incubation in the presence of several metabolites. After solubilization of the enzymes, the membranes present free sites for specific binding of glucokinase, therefore, they can be purified by affinity chromatography on Sepharose--ATP-glucokinase. This method yields membranous vesicles which contain, in addition to glucokinase, uridylyl-transferase, phosphoglucomutase, sialyl-transferase and adenylate cyclase. Galactosyl-transferase, glucose-6-phosphatase and NADPH cytochrome c reductase are absent. It appears that functionally related enzyme from UDP-glucose biosynthesis are aggregated onto specific patches of the membrane, most likely from Golgi apparatus.

Animals↗
PubMed1978

[Presence of enzymes catalyzing UDP-glucose biosynthesis in a low density Golgi fractions of cat hepatocytes].

A Golgi-rich fraction is prepared from cat hepatocytes by the means of a four-step sucrose density gradient. The material applied to this gradient is composed either of smooth microsomes prepared from healthy animals, or of total microsomes prepared from cat treated by 50 per cent ethanol (0.6 g/100 g body weight, administered by stomach tube). A light fraction (d : 1.10) is obtained by the two procedures. It does not show any glucose-6-phosphatase activity, but is enriched in sialyltransferase, known as a marker enzyme for Golgi apparatus. It also contains the three enzymes implicated in the biosynthetic pathway for UDP-glucose (glucokinase, phosphoglucomutase and UTP : glucose-1-phosphate uridylyltransferase). UDP-glucose being the ultimate substrate in membranous glucosylation reactions, these results could support the hypothesis that sugar-nucleotides necessary for the glycoprotein biosynthesis are produced in the Golgi vesicles directly.

Animals↗
PubMed1977

[Presence of a pathway for biosynthesis of UDP-glucose in the Golgi apparatus of rat hepatocytes].

Glucokinase, phosphoglucomutase and glucose-1-phosphate uridylyltransferase are the three enzymes involved in a microsomic pathway for the synthesis of UDP glucose. Evidence is given, in this paper, for the localization of these three enzymes in a Golgi-rich fraction of rat liver. This fraction is prepared, from smooth microsomes, by the means of a discontinuous four-step sucrose gradient. Three of the lighter fractions (d = 1.08-1.13) are enriched in the Golgi markers (galactosyltransferase, sialytransferase and thiamin pyrophosphatase), especially the one with density 1.13. The three enzymes we are interested in are enriched in the two upper hands (d 1.08-1.11), which display an activity for the biosynthesis of UDP-glucose from glucose equivalent to the one obtained in a crude microsomic preparation, and which are not contaminated by other subcellular components.

Animals↗
PubMed1977

[Liberation and reassociation of the microsomal membrane glucokinase in cat liver].

The particulate glucokinase of cat liver is shown to be microsomal. The activity is readily solubilized by glucose-6-phosphate, ATP, pyrophosphate, high salt concentrations and, to a lesser extent, ribonucleoside triphosphates. The solubilization by glucose-6-phosphate is inhibited by Pi. Solubilizations by ATP and glucose-6-phosphate differ in their sensitivity to temperature changes; they are relatively specific for glucokinase as compared to solubilization by detergent (Triton X 100). The enzyme can be bound again to previously eluted microsomal membranes. Treatment of membrane with trypsin, at 0 degrees C, destroys the ability to rebind the enzyme to the membrane. It is suggested that electrostatic forces are of considerable importance for the binding of glucokinase to a possible protein binding site in the membrane.

Animals↗
PubMed1976

[Galactose transfer in the membranes of human milk fat globules (author's transl)].

Galactosyltransferase which catalyzes the transfer from UDP-galactose to either endogeneous glycoproteins, free N-acetylglucosamine or N-acetylglucosaminyl residues in the carbohydrate portion of glycoproteins, or to glucose when alpha-lactalbumin is added, occurs in human milk fat globule membranes. Various treatments (washing of membranes, freezing and thawing) did not affect this activity. In the presence of Triton X-100, the enzyme shows appreciable latency, This detergent was then used to solubilize the enzyme and to study its main characteristics. A competition and a heat stability experiment show that only one enzyme acts on two substrates (free N-acetylglucosamine or desialyzed and degalactosylated fetuin). UDP-galactose hydrolase activities were very low compared to those of the bovine milk fat globule membranes. Other characteristic enzymes of Golgi vesicles were found in human milk fat globules membranes. It is of interest to find out whether this is the result of contamination with cytoplasmic particles or whether it reflects the participation of Golgi vesicles in human milk fat globule secretion.

Enzyme Activation↗
PubMed1976

[Amino acid incorporation by human milk fat globules membranes (author's transl)].

Human milk fat globule membranes (MFGM) can incorporate radioactive 14C amino acids in a hot trichloracetic acid-insoluble material. Aspecific adsorption and bacterial contamination are unlikely. The products of protein synthesis were analyzed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate or by action of proteolytic enzymes. Various inhibitors of protein synthesis were assayed. Fragments of rough endoplasmic reticulum or mitochondria could be involved in this incorporation.

Amino Acids↗
PubMed1976

[Perparation and comparative analytical study of cat liver microsomes].

Cat liver homogenates have been fractionated by differential centrifugation. Four particulate fractions (1 000 X g, 10 000 X g, and 145 000 X g) and a supernatant have been obtained. The biochemical composition of these fractions has been established from the assay and distribution pattern of 22 enzymatic and chemical constituents including marker enzymes for mitochondria, lysosomes, peroxisomes, plasma membranes, endoplasmic reticulum, Golgi apparatus and cell sap. The microsomal fraction was characterized by a moderate contamination with large cytoplasmic granules and by a low yield in protein and cholesterol. It contained 50 per cent of Golgi complex and about 40 per cent of plasma membranes. Morphological analysis of subcellular fractions was performed and confirmed biochemical results.

Animals↗