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G Azzar

Publications and source records attributed to G Azzar.

26 records · Page 2Linked to original sources
PubMed1983

Properties of uridine diphosphate glucose pyrophosphorylase from Golgi apparatus of liver.

Golgi apparatus isolated from cat liver contained UDPglucose pyrophosphorylase (UTP:alpha-D-glucose-1-phosphate uridylyltransferase, EC 2.7.7.9) activity. The results of washing suggested that pyrophosphorylase was bound firmly to Golgi membranes. Moreover, the enzyme was activated by Triton X-100 in the same extent as galactosyltransferase, a typical Golgi apparatus enzyme. Two-substrate kinetic studies were performed with the enzymes from cytosol and Golgi fractions. The soluble enzyme showed an apparent 2.5-fold greater activity for the glucose 1-phosphate than for UTP, while pyrophosphorylase of Golgi apparatus had the same affinity for the two substrates. A random mechanism was observed with a direct dependence of apparent Michaelis constant values on the concentration of second substrate for soluble enzyme. In contrast, with Golgi enzyme one ligand had no effect on the binding of the other.

Animals↗
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

[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

[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↗