Fructoses uptake

Fructose is present outside a cell at 1 /iM concentration. An active transport system in the plasma membrane transports fructose into this cell, using the free energy of ATP hydrolysis to drive fructose uptake. Assume that one fructose is transported per ATP hydrolyzed, that ATP is hydrolyzed on the intracellular surface of the membrane, and that the concentrations of ATP, ADP, and Pi are 3 mM, 1 mM, and 0.5 mM, respectively. T = 298 K. What is the highest intracellular concentration of fructose that this transport system can generate Hint Kefer to Chapter 3 to recall the effects of concentration on free energy of ATP hydrolysis.)... 

Fructose is the fuel provided in the semen. The advantage of this is that it is transported across the plasma membrane of the sperm by the transporter protein that is specific for fructose, the GLUT-5 transporter. Since the cells of the vagina and the uterus do not possess this transporter, fructose uptake and oxidation is restricted to the spermatozoa. 

Bizukojc, M. and Ledakowicz, S. 2004. The kinetics of simultaneous glucose and fructose uptake and product formation by Aspergillus niger in citric acid fermentation. Process Biochemistry 39 2261-2268. 

Fig. 2.—Routes180 ofD-Fructose Uptake and Metabolism in Arthrobacter pyridinolis. (Open circles represent inducible proteins, and hatched circles represent phosphate constitutive proteins involved in transport PEP = enolpyruvate phosphate.)...

Schutz, M. and J. Gafner. 1995. Lower fructose uptake capacity of genetically characterized strains of Saccharomyces bayanus compared to strains of Saccharomyces cerevisiae a likely cause of reduced alcoholic fermentation activity. Am.J. Enol. Vitic. 46 175-180. 

Uptake was inducible by the substrate, did not occur with fructose-grown cells, and was inhibited by cyanide that prevents development of a protomotive force, and by the protophore carbonylcyanide-3-chlorophenylhydrazone (Leveau et al. 1998). The protein involved was encoded by an open reading frame on the plasmid designated tfdK. 

GLUT-2 has high activity in liver to maintain transport close to equilibrium for both uptake and release of glucose (see below). It can also transport galactose, mannose and fructose - all of which can be converted to glucose in the liver. 

The toxic effect of fluoroacetate was studied in an experiment using intact isolated rat heart. After the heart was perfused with 0.22 mM fluoroacetate, the measured rate of glucose uptake and glycolysis decreased, and glucose 6-phosphate and fructose 6-phosphate accumulated. Examination of the citric acid cycle intermediates revealed that their concentrations were below normal, except for citrate, with a concentration 10 times higher than normal. 

Figure 11-2 Roles of phosphofructose kinase and fructose 1,6-bisphosphatase in the control of the breakdown and storage (—+) of glycogen in muscle. The uptake of glucose from blood and its release from tissues is also illustrated. The allosteric effector fructose 2,6-bisphosphate (Fru-2,6-P2) regulates both phosphofructokinase and fructose 2,6-bisphosphatase. These enzymes are also regulated by AMP if it accumulates. The activity of phosphofructokinase-2 (which synthesizes Fru-2,6-P2) is controlled by a cyclic AMP-dependent kinase and by dephosphorylation by a phosphatase.

The photosynthetic block precedes sucrose synthesis, and sucrose partially reverses the inhibition caused by the lack of fixation of carbon dioxide. D-Fructose disappears first, after treatment, followed by sucrose, and then u-glucose.188 It is likely that other metabolic systems are involved as well, since the amino acid distributions were not identical to the I4C02 dark-fixation products.189 Uptake of sucrose-14C increased some acids (as-... 

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