Glucose transport fructose

Before glycolysis from glucose can begin, glucose has to be transported into the ceU. This is achieved by a transporter protein, in the plasma membrane (Chapter 5). There are five different types of glucose transporter, all encoded by separate genes. The proteins have slightly different properties, different tissue distribution and somewhat different roles in these tissues. Their roles are briefly described in Table 6.1. A sixth transporter is specific for fructose it is... 

Sugar The hydrolysis of sucrose in the intestine produces both glucose and fructose, which are transported across the epithelial cells by specific carrier proteins. The fructose is taken up solely by the liver. Fructose is metabolised in the liver to the triose phosphates, dihydroxy-acetone and glycer-aldehyde phosphates. These can be converted either to glucose or to acetyl-CoA for lipid synthesis. In addition, they can be converted to glycerol 3-phosphate which is required for, and stimulates, esterification of fatty acids. The resulting triacylglycerol is incorporated into the VLDL which is then secreted. In this way, fructose increases the blood level of VLDL (Chapter 11). 

The third group is that of compounds which may potentially be transported by the PTS and inhibit cAMP production. Cellulase synthesis is initiated after these compounds are consumed for cell growth. This group includes D-glucose, D-fructose, maltose, mannitol, glycerol, sorbitol, and -methyl glucoside. The presence of these compounds in Solka Floe fermentations, enhanced enzyme yields (132 to 254%) but the time required to complete cellulase synthesis took longer (106 to 148%) than the control. 

A protein family involved in transporting hexoses into mammalian tissues Facilitative glucose transporter, which is insulin-sensitive A fructose transporter, catalyzes the uptake of fructose Genetically modified... 

Connecting peptide of insulin Cytosine triphosphate Extracellular fluid Essential fatty acid Endoplasmic reticulum Fructose- I bisphosphate Flavin adenine dinucleotide Free fatty acid Formiminoglutamtc acid Glucose transporter gene or protein... 

GLUTS (small intestine) Small intestine, kidney, skeletal muscle, brain, and adipose tissue Transports fructose (not glucose)... 

The availability of metabolites for sucrose synthesis and the need for products of sucrose degradation regulate gene expression. For respiration, sucrose is hydrolyzed by invertase to free glucose and fructose, which are phosphorylated and undergo glycolysis to pyruvate. The pyruvate is then either metabolized by mitochondrial electron transport to ATP and NADH (respiration), or metabolized to provide starting products for amino acid, lipid, and nucleotide syntheses. 

Inukai K, Katagiri H, Takata K, Asano T, Anai M, et al. 1995. Characterization of rat GLUTS and functional analysis of chimeric proteins of GLUTl glucose transporter and GLUTS fructose transporter. Endocrinology 136 4850-4857. 

Page, P., Blonski, C., and Perie, J., An improved chemical and enzymatic synthesis of new fructose derivatives for import studies by the glucose transporter in parasites. Tetrahedron. 52, 1557, 1996. 

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