PubMed · 10503438
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M Ida. 1999. [Aldolase].. https://pubmed.ncbi.nlm.nih.gov/10503438/
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Fructose 1,6-bisphosphate aldolase, a glycolytic enzyme, catalyzes the cleavage of fructose 1,6-bisphosphate, resulting in two three-carbon products. The reaction of the class I enzymes, which utilize a Schiff-base intermediate, requires that the hexose be in the open-chain form. This form comprises only 1-2% of the sugar at equilibrium. The chemical form of the substrate that binds to aldolase and begins the catalytic cycle has not been unequivocally demonstrated. Transient-state kinetics in single-turnover experiments of fructose 1,6-bisphosphate with aldolase in excess reveals the rates of the intermediate steps in the cleavage reaction, including those from initial binding to Schiff-base formation. The rate of hexose Schiff-base formation was faster than the uncatalyzed rate for ring-opening of either the alpha- or beta-furanose at 4 degrees C. In addition, approach-to-equilibrium experiments reveal that aldolase binds and reacts first with 70% of fructose-1,6-bisphosphate in a fast reaction, consistent with the amount of beta-anomer in solution, and with the remaining 30%, presumably the alpha-anomer, in a slow reaction. These results indicate that aldolase must catalyze the ring-opening step and that there may be a previously unrecognized second active site on the enzyme for catalyzing this reaction.
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We describe here different regulation of the AldP gene, a nuclear gene encoding chloroplast aldolase, in different tissues and growth ages of rice seedlings. Expression of the AldP gene is mesophyll cell-specific, and increases from the basal to the upper region in each leaf. The gene expression is repressed in the dark-grown leaf blade, but is induced by a short-term-exposure to light, to a level higher than that seen in the normal leaf blade. However, the light-inducibility differs among the tissues, and shows different patterns among leaf positions; i.e., the extent of light-induction is higher in the third leaf blade as compared with the earlier developed second leaf blade. Such positional differences in the regulation are also seen in the leaf sheath. These responses are not accompanied by changes of the cell type specificity in the expression.