Presence Of Phlorizin Research Articles

Transport of 3-O-methyl-D-glucose into mammalian pancreatic -cells.

The transport and oxidation of 3-O-methyl-d-(U-14C)glucose was studied in microdissected pancreatic islets of obese-hyperglycemic mice. There was no significant production of14CO2 during incubation for 2 h. A comparison with the uptake of sucrose and mannitol indicated that 3-O-methyl-d-glucose was uniformly distributed across the β-cell plasma membrane. Externald-glucose inhibited the entry of 3-O-methyl-d-glucose and caused a significant net loss of 3-O-methyl-d-glucose from islets equilibrated with this compound. The transport of 3-O-methyl-D-glucose was also markedly reduced in the presence of phlorizin or phloretin, whereasd-mannoheptulose ord-glucosamine exerted a slight inhibition. The results support our hypothesis that the transport ofd-glucose into the pancreatic β-cells is carriermediated, and indicate that 3-O-methyl-d-glucose is a non-metabolizable substrate for this carrier in the pancreatic islets. Since in contrast tod-glucose 3-O-methyl-d-glucose does not stimulte insulin release from the type of islets used, the secretagoric recognition system ford-glucose is probably not identical with the membrane transport system.

Separate transport systems for sugars and amino acids in developing rat kidney cortex.

The ability of renal cortical slices of newborn and young rats to accumulate a nonmetabolizable sugar, alpha-methylglucoside, is slight and does not reach adult capacity until 25 days of age. However, a rudimentary sugar transport system is present, as indicated by a further decrease in accumulation in the presence of phlorizin or absence of sodium ion.Amino acid uptake in immature kidney tissue is not deficient; on the contrary, the tissue took up and concentrated more glycine and lysine than adult tissue. Decreased amino acid efflux from the immature cells appears to be the explanation. Concentration dependence of amino acid uptake was the same in 5-day-old and adult tissue. These differences between the transport characteristics of a model sugar and representative amino acids during development indicate separate transport systems for the two types of substrate.

Properties of ATPase in chloroplasts

1. 1. Mg 2+-ATPase (light-triggered Mg 2+-dependent ATPase) activity in chloroplasts was stimulated by atebrin, NH 4Cl and gramicidin when the uncouplers were added after light triggering. The stimulation was followed in time by inhibition when the reaction took place in the dark. 2. 2. This inhibition of Mg 2+-ATPase activity was overcome when the reaction was carried out under continuous illumination. 3. 3. The energy transfer inhibitors of photophosphorylation, phlorizin and Dio-9, inhibited Mg 2+-ATPase activity and the extent of inhibition increased with time. The inhibition by Dio-9 was partially reversed by light while that of phlorizin was not. 4. 4. Light-triggered ATP-P i exchange activity in chloroplasts was inhibited by both atebrin and phlorizin. The extent of the inhibition increased with time. 5. 5. The activity of a soluble Ca 2+-ATPase was inhibited by Dio-9, phlorizin, NH 4Cl and atebrin. The kinetics of activity was linear with time, except in the presence of phlorizin. 6. 6. These results are interpreted as indicating a requirement of a high-energy state for triggering and maintenance of Mg 2+-ATPase and ATP-P i exchange reactions. The relation of ATPase activity to the coupling mechanism in chloroplasts is discussed.

The effect of phlorizin on the multiplication of measles virus

Phlorizin in a concentration of 5 × 105 M or higher prevented the syncytium-forming long-term cytopathic effect of measles virus both in a cell line, Lu 106 cells, and in primary dog kidney cells. The presence of phlorizin resulted in a retardation of extracellular accumulation of biologically active virus products. In Lu 106 cells the final yield of virus material was considerably increased and after equilibrium centrifugation in CsCl gradients, the products mainly accumulated at a density range of 1.23 to 1.25 g/cc. No increase in antigen quantities was obtained in primary dog kidney cells maintained on medium containing phlorizin, although there was an increase in hemagglutinin titers. Centrifugation in CsCl gradients demonstrated that the products obtained in the presence of phlorizin from this slow-growing virus-cell system still appeared markedly heterogeneous.

Insulin, anaerobiosis, and phlorizin in entry of D-galactose into skeletal muscle.

In the eviscerate-nephrectomized rat the increase in the galactose space seen after insulin was significantly prevented by phlorizin in concentrations which by themselves were without effect on this function. Similarly, the d-galactose uptake by rat diaphragm was increased by insulin, and this effect was also significantly reduced by phlorizin in concentrations that had no effect on d-galactose uptake in the absence of insulin. The increased uptake of d-galactose by the rat diaphragm incubated in nitrogen was also significantly reduced in the presence of phlorizin.

EFFECTS OF METABOLIC INHIBITORS ON POTASSIUM-STIMULATED GLUCOSE ABSORPTION BY ISOLATED SURVIVING GUINEA PIG INTESTINE

2,4-Dinitrophenol, at low concentrations, inhibits potassium-stimulated active transport of glucose by the isolated surviving guinea pig intestine to a greater extent than the unstimulated glucose transport. The potassium stimulation is abolished in the presence of 0.04 mM 2,4-dinitrophenol. Potassium stimulation of the active transport of glucose and galactose in the isolated guinea pig intestine is inhibited by phlorizin at low concentrations (0.01 mM) which have little or no effect on the unstimulated sugar transport. The presence of phlorizin has little or no effect on active fructose absorption, as shown by the combined transport of fructose and glucose derived from the fructose. In the presence of 15.6 meq./liter K+phlorizin exerts a small depression of the active transport of fructose. Potassium stimulation of the active transport of glucose in the isolated guinea pig intestine is inhibited by the narcotic luminal at low concentrations (2 mM). Luminal (10 mM) abolishes the potassium stimulation. Sodium malonate, at the concentration 2 mM, which exerts no inhibition of active glucose transport in isolated surviving guinea pig intestine, brings about over 40% inhibition of glucose transport when this is stimulated by potassium ions. Choline, at 0.5 mM, suppresses potassium stimulation of the active glucose transport in the isolated surviving guinea pig intestine. It is suggested that an enzymatic mechanism exists, associated with intestinal membranes, that controls sugar transport and that phosphorylations, either directly or indirectly, are connected with it.

EFFECTS OF METABOLIC INHIBITORS ON POTASSIUM-STIMULATED GLUCOSE ABSORPTION BY ISOLATED SURVIVING GUINEA PIG INTESTINE

2,4-Dinitrophenol, at low concentrations, inhibits potassium-stimulated active transport of glucose by the isolated surviving guinea pig intestine to a greater extent than the unstimulated glucose transport. The potassium stimulation is abolished in the presence of 0.04 mM 2,4-dinitrophenol. Potassium stimulation of the active transport of glucose and galactose in the isolated guinea pig intestine is inhibited by phlorizin at low concentrations (0.01 mM) which have little or no effect on the unstimulated sugar transport. The presence of phlorizin has little or no effect on active fructose absorption, as shown by the combined transport of fructose and glucose derived from the fructose. In the presence of 15.6 meq./liter K+phlorizin exerts a small depression of the active transport of fructose. Potassium stimulation of the active transport of glucose in the isolated guinea pig intestine is inhibited by the narcotic luminal at low concentrations (2 mM). Luminal (10 mM) abolishes the potassium stimulation. Sodium malonate, at the concentration 2 mM, which exerts no inhibition of active glucose transport in isolated surviving guinea pig intestine, brings about over 40% inhibition of glucose transport when this is stimulated by potassium ions. Choline, at 0.5 mM, suppresses potassium stimulation of the active glucose transport in the isolated surviving guinea pig intestine. It is suggested that an enzymatic mechanism exists, associated with intestinal membranes, that controls sugar transport and that phosphorylations, either directly or indirectly, are connected with it.

Absorption of amino acids from isolated surviving intestine

1. 1. The l-isomers of histidine and alanine are absorbed at a more rapid rate than the respective d-isomers from the isolated surviving guinea pig intestine. 2. 2. Increase of concentration of dl-alanine above 0.01 M results in a progressively smaller increment in rate of absorption. Above 0.02 M, the increase in absorption is probably due to increase in the amount of diffusion and not to increase in “active” absorption. 3. 3. Anaerobiosis diminishes absorption of dl-alanine. The presence of 10 −4 M dinitrophenol diminishes the rate of active absorption of both dl-alanine and l-phenylalanine. 4. 4. The presence of phlorizin does not inhibit the active absorption of either dl-alanine or l-phenylalanine from the isolated surviving guinea pig intestine. 5. 5. The presence of 0.01 M deoxypyridoxine inhibits the absorption of dl-alanine from isolated surviving guinea pig intestine. This inhibition is not reversed by the presence of any of the following: 5 × 10 −3 M pyridoxal, 10 – M pyridoxine, 3 × 10 −3 M pyridoxamine phosphate, and 1.2 × 10 −3 M calcium pyridoxal phosphate. The presence of 10 −2 M pyridoxine does not inhibit the absorption of dl-alanine. 6. 6. The presence of 10 −2 M deoxypyridoxine also inhibits the active absorption of glucose and fructose, pointing to an inhibitory action of deoxypyridoxine on the mechanisms underlying “active” absorption in general from the isolated intestine. 7. 7. A high concentration of glucose (0.278 M) inhibits the absorption of dl-alanine. This effect is likely to be due to osmotic effects, as sorbose at the same concentration has a similar inhibitory effect. High concentrations of sodium chloride in the lumen are also inhibitory to the amino acid absorption. 8. 8. l-Glutamine is absorbed unchanged and at a greater rate than l-glutamate at equivalent concentrations. In contrast to l-glutamate, l-glutamine is “actively” absorbed by the isolated surviving guinea pig intestine. 9. 9. Asparagine absorption by the isolated surviving guinea pig intestine results in its conversion to aspartate and ammonia which appear in the serosal solution. No asparagine appears in this solution. l-Asparagine undergoes some “active” absorption, in contrast to dl-aspartate which shows none. The rate of absorption of l-asparagine is smaller than that due to an equivalent concentration of l-glutamine.

The Effect of Phlorizin on the Metabolism of Cytolysing Sea-Urchin Eggs

ABSTRACT Unfertilized sea-urchin eggs produce acid when they are cytolysed or fertilized (Ashbel,, 1929; Runnstr öm, 1933 a, 1935). Neither the post-fertilization nor the post-cytolysis acid has been identified. The number of different acids which might be released is large, and it has not so far been considered expedient to attempt direct analysis of the sea water surrounding the activated eggs. One way of establishing the nature of the acid is by observing the effect of specific metabolic inhibitors on its production. Runnström (1933 b, 1935) used this technique, but the inhibitors used were all negative in their effect, i.e. they did not inhibit acid production. Runnströom investigated the effect of inhibitors which affect one type of glycolysis.1 This paper is also concerned with the effect of a glycogen breakdown inhibitor. If the acid production after cytolysis is associated with the formation of hexose phosphate from glycogen, it should be partly or wholly inhibited in the presence of phlorizin (Lundsgaard, 1933).