BLBS102-c27 BLBS102-Simpson March 21, 2012 13:25 Trim: 276mm X 219mm Printer Name: Yet to Come
27 Biochemistry of Fruits 541Glucose Glucose-6-phosphateDihydroxyacetone phosphateFructose-6-phosphatePhosphofructokinaseFructose-1,6-bisphosphate1,3-DiphosphoglycerateGlycerate-3-phosphate kinase3-Phosphoglycerate 2-PhosphoglyceratePhosphoenol pyruvatePyruvate dehydrogenasePyruvateAcetyl CoAAnaerobic metabolismBreakdown of sugars: Glycolysis/citric acid cycleCitric acid cycleCO 2CO 2CO 2Phosphoglycerate mutaseEthanol
Alcohol
dehydrogenasePyruvate
decarboxylaseCitrate synthase Citrate AconitaseIsocitrateIsocitrate
dehydrogenaseMalate
dehydrogenaseOxaloacetateMalateFumaraseFumarateSuccinate
dehydrogenase SuccinateCoash Succinate thiokinaseSuccinyl CoACOA-SHα-KetoglutarateAcetaldehydeEnolaseAldolaseTriose phosphate
isomeraseGlyceraldehyde-3-phosphateGlyceraldehyde-3-phosphate
dehydrogenaseHexokinaseHexosephosphate isomerase
AT PAT PAT PAT PADPADPNADNADNADNADNADNADFADFADH 2NADHNADHNADHNADHNADH
ATP ADPNADHADPADPFigure 27.3.Catabolism of sugars through glycolytic pathway and citric acid cycle.alteration of PFK, which increases the efficiency of utilisation
of fructose-6-phosphate, is another means of regulation that can
activate the carbon flow through the glycolytic pathway.
Other enzymes of the glycolytic pathway are involved in
the regulation of starch/sucrose biosynthesis (Figs. 27.2 and
27.3). Fructose-1,6-bisphosphate is converted back to fructose-
6-phosphate by the enzyme fructose-1,6-bisphosphatase, also
releasing inorganic phosphate. This enzyme is localised in
the cytosol and chloroplast. Fructose-6-phosphate is convertedto fructose-2,6-bisphosphate by fructose-6-phosphate 2-kinase
which can be dephosphorylated at the 2 position by fructose-
2,6-bisphosphatase. Fructose-6-phosphate is an intermediary in
sucrose biosynthesis (Fig. 27.2). SPS is regulated by reversible
phosphorylation (a form of post-translational modification that
involves addition of a phosphate moiety from ATP to an OH-
amino acid residue in the protein, such as serine or threonine, me-
diated by a kinase, and dephosphorylation mediated by a phos-
phatase) by SPS kinase and SPS phosphatase. Phosphorylation