[Perparation and comparative analytical study of cat liver microsomes]

[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.

The hepatic cytochrome level in the cat (Felis catus): normal value and variations in relation to some biological parameters

1. The average level of the hepatic hydroxylating cytochrome was determined in the cat (0.380 +/- 0.085 nmol.mg-1 proteins). 2. Great individual differences were noted. 3. The level of cytochrome increases with age in the immature (age less than or equal to 8.5 months) and young adults (age: 10-18 months). It is diminished in the older animals. 4. The measured average level is lower than that in other species, and approaches the human one. 5. The induction capacity of phenobarbital is lower in the cat than in other mammals, for example the rat or the mouse.

[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.

[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.