Metabolism of glucose 1,6-P2-III. Partial purification and characterization of glucose 1,6-P2 synthase from pig skeletal muscle
University of Barcelona, Barcino, Catalonia, SpainComparative biochemistry and physiology. B, Comparative biochemistry (Impact Factor: 2.07). 02/1988; 90(4):739-44. DOI: 10.1016/0305-0491(88)90328-8
1. Glycerate 1,3-P2-dependent glucose, 1,6-P2 synthase has been purified 2000-fold from pig skeletal muscle, with a yield of 75%. 2. The enzyme possesses fructose 1,6-P2-dependent glucose 1,6-P2 synthase and phosphoglucomutase activities, which represent 0.1 and 60% of the main activity, respectively. 3. Both glucose 1-P and glucose 6-P can act as acceptors of the phosphoryl group from glycerate 1,3-P2. 4. The Km values are 19 microM and 67 nM for glucose 1-P and glycerate 1,3-P2, respectively. 5. The enzyme is inhibited by glycerate 2,3-P2, fructose 1,6-P2, glycerate 3-P, phosphoenolpyruvate and lithium, the inhibition pattern varying with the compound.
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ABSTRACT: 1. To compare glucose 1,6-bisphosphate synthesis in different types of cells, we partially purified (2000-fold) a glycerate 1,3 P2-dependent glucose 1,6-bisphosphate synthase from rabbit skeletal muscle. 2. In agreement with the results reported by others for mouse brain and pig skeletal muscle, the enzyme can be separated from bulk phosphoglucomutase (PGM) activity by DEAE-cellulose chromatography of crude cellular extract. This cannot be achieved on human hemolysates where glycerate 1,3-P2-dependent glucose 1,2-bisphosphate synthesis is displayed only by multifunctional PGM2 isoenzymes. 3. The Km values for glycerate 1,3-P2 (0.50 microM), glucose 1-phosphate (90 microM), Mg2+ (0.22 mM), and also pH optimum (7.8) and mol. wt (70,000) of the rabbit skeletal muscle enzyme are similar to those of the enzymes from mouse brain and human red blood cells, but they differ from those reported for the pig skeletal muscle enzyme.
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ABSTRACT: Knowledge of luminal and basolateral acinar cell membrane areas of the secretory endpieces is a prerequisite for a detailed quantitative analysis of the ion transport involved in secretion of the primary saliva. In the present study, these areas were estimated in rat parotid acinar cells using standard stereological methods. A total of 480 micrographs--obtained by random sampling from eight glands from four rats--were analysed at a final magnification of 40000x. Expressed per unit cell volume, the area of the luminal acinar cell membrane was: 0.125 micron 2.micron-3 (SEM = 0.027 micron 2.micron-3, n = 4 animals) and the area of the basolateral membrane was: 1.54 microns 2.micron-3 (SEM = 0.085 micron 2.micron-3, n = 4 animals). These figures make it possible to perform a synthesis based upon different categories of experimental data, e.g. on ion fluxes, membrane potentials and single-channel conductances. Thus, we have estimated the density of open, low-conductance Cl- channels in the luminal membrane--which are not readily accessible for direct, patch-clamp analysis--to be approximately 18 channels per microns 2 in the stimulated state.
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