Glucose-6-phosphate intracellular

Insulin stimulates lipogenesis by several other mechanisms as well as by increasing acetyl-CoA carboxylase activity. It increases the transport of glucose into the cell (eg, in adipose tissue), increasing the availability of both pyruvate for fatty acid synthesis and glycerol 3-phosphate for esterification of the newly formed fatty acids, and also converts the inactive form of pyruvate dehydrogenase to the active form in adipose tissue but not in liver. Insulin also—by its ability to depress the level of intracellular cAMP—inhibits lipolysis in adipose tissue and thereby reduces the concentration of... 

It is an important intracellular reductant, helping to maintain essential SH groups of enzymes in their reduced state. This role is discussed in Chapter 20, and its involvement in the hemolytic anemia caused by deficiency of glucose-6-phosphate dehydrogenase is discussed in Ghapters 20 and 52. 

Hemolytic anemia results from decreased RBC survival time due to destruction in the spleen or circulation. The most common etiologies are RBC membrane defects (e.g., hereditary spherocytosis), altered Hb solubility or stability (e.g., sickle cell anemia [see Chap. 34] and thalassemias), and changes in intracellular metabolism (e.g., glucose-6-phosphate dehydrogenase deficiency). Some drugs cause direct oxidative damage to RBCs (see Appendix 3). 

Of course, it is now established that the glycolysis of glucose to carbon dioxide and ethanol occurs by way of a complex pathway involving 10 different enzymes acting on a variety of sugar phosphate intermediates. The extracellular enzyme preparation that Fischer used was termed invertin, the origin of the term for the enzyme we now know as invertase. He termed the intracellular enzyme yeast-glucase (31) and this enzyme is of the type we now refer to as an amylase. 

Calculate Keq for the overall reaction. For the ATP-dependent phosphorylation of glucose, what concentration of glucose is needed to achieve a 250 /xm intracellular concentration of glucose 6-phosphate when the concentrations of ATP and ADP are 3.38 mM and 1.32 mM, respectively Does this coupling process provide a feasible route, at least in principle, for the phosphorylation of glucose in the cell Explain. 

Mannose, the C-2 epimer of glucose (see p. 84), is an important component of glycoproteins (see p. 164). Hexokinase phosphorylates mannose, producing mannose 6-phosphate, which, in turn, is (reversibly) isomerized to fructose 6-phosphate by phosphoman-nose isomerase. [Note There is little mannose in dietary carbohydrates. Most intracellular mannose is synthesized from fructose, or is preexisting mannose produced by the degradation of structural carbohydrates and salvaged by hexokinase.]... 

---