Hexose metabolism

The Pentose Phosphate Pathway Other Pathways of Hexose Metabolism... 

THE PENTOSE PHOSPHATE PATHWAY OTHER PATHWAYS OF HEXOSE METABOLISM / 165... 

Two metabolic patterns are discernible from the results. Carbon atoms 2, 1, and 7 of shikimate (VI) are derived almost equally from G-1,6, G-2,5, and G-3,4, respectively. In the Embden-Meyerhof pathway of hexose metabolism (see Fig. 2), D-fructose 1,6-diphosphate is cleaved to 1,3-dihydroxy-2-propanone phosphate (G-1,2,3) and D-glycerose 3-phosphate (G-4,5,6), and the two trioses are interconverted by triose phosphate isomerase. The observed randomization of label between Cl and C6, C2 and C5, and C3 and C4 of hexose therefore implies that C2, Cl, and C7 of shikimate are derived from a 3-carbon intermediate of glycolysis. The small but significant preponderance of G-6 over G-1, of G-5 over G-2, and, presumably, of G-4 over G-3, can be explained by recent observations that, in the aldolase cleavage of D-fructose 1,6-diphosphate, the 1,3-dihy-... 

They are divided into two groups in relation to their hexose metabolism ... 

Whilst the majority of investigations into halophilic hexose metabolism has been concerned with the catabolism of glucose, it has been recently reported [104,105] that Haloarcula vallismortis catabolises fructose via a modified Embden-Meyerhof pathway. Fructose is phosphorylated to fructose 1-phosphate via a ketokinase, and is then converted to fructose 1,6-bisphosphate via 1-phosphofructokinase. Aldol cleavage generates dihydroxyacetone-phosphate and glyceraldehyde 3-phosphate, both of which can be further metabolised via the glycolytic sequence described earlier. It remains to be established whether other halophilic archaebacteria can also catabolise fructose in this manner. 

Regulation of Hexose Metabolism in Multicellular Eukaryotic Organisms. 2418... 

Within experimental limits, leaves labeled with l-[5- C]- or l-[6- C]ascorbic acid gave comparable results (Table III). Additively, the C in CO2, sugars, and malic acid accounted to 62-63% of that present in the leaves. Another 7% appeared in the residue as glycans. The total amount of C found in hexose or products of hexose metabolism of l-[5- C]- or L-[6- C]ascorbic acid labeled leaves was similar to that found in tartrate (and CO2) after labeling with l-[1- C]- or l-[4- C]-ascorbic acid. Cleavage of the carbon chain of ascorbic acid at the C4-C5 bond accounts for these observations. 

Fig. 4. Dimerization and phosphorylation of Hxk2. Hexokinase PII (Hxk2) was one of the first proteins to be implicated in glucose repression and adaptation to fermentative metabolism. However, its role is still unclear. Hxk2 is a phosphoprotein which exists in a mono- or dimeric state. Only the monomer is phosphorylated. Hxk2 is found in the cytoplasm and the nucleus which suggests that it may play roles in both hexose metabolism and transcriptional regulation [76,77]...

Acetyl CoA can be converted to fatty acyl CoA by one of two routes. One utilises 3-hydroxyacyl CoA dehydrogenase and the other, which proceeds via malonyl CoA, uses acetyl CoA carboxylase. The former route is considered to be reversible and 3-hydroxyacyl CoA dehydrogenase is therefore an enzyme of fatty acid oxidation also. When formed, fatty acyl CoA can be incorporated into other lipids as shown in Figure 2.11. Palmityl CoA, however, has other important utilisation routes leading to the synthesis of sphingomyelins (phospholipid) or ceramide hexosides. The latter represent an important junction of lipid and hexose metabolism and are precursors of the gangliosides which contain hexose, hexosamine, and A -acetylneuraminic acid (referred to briefly under glycolipid synthesis above). 

Viola R. 1996. Hexose metabolism in discs excised from developing potato (Solatium tuberosum L.) tubers. II. Estimations of fluxes in vivo and evidence that fructokinase catalyses a near rate-limiting reaction. Planta 198 186-196. 

Ramirez, R., Sener, A., and Malaisse, W.J., 1995. Hexose metabolism in pancreatic islets effect of D-glucose on the mitochondrial redox state. Molecular and Cellular Biochemistry. 142 43-48. 

A rough estimate of the hexose metabolism of flying insects which is about 100-fold higher than at rest is given by Sacktor [87]. A 50 mg insect should consume in the average an amount of 30 pmol hexose/(g-min) in flight and have a yield of -1300 kJ/mol O2. 

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