Fructose 1,6-bisphosphatase, function

The fructose bisphosphatase of green plants has an amino acid sequence which is very similar to those of the corresponding enzymes isolated from other sources such as yeast or mammals, except that the plant enzyme has an additional sequence of 20 or so amino acids that has no counterpart in the enzymes found in the other species. What function might this additional sequence have in the plant enzyme ... 

There are three mechanistic possibilities for catalysis by two-metal ion sites (Fig. 10). The first of these is the classic two-metal ion catalysis in which one metal plays the dominant role in activating the substrate toward nucleophilic attack, while the other metal ion furnishes the bound hydroxide as the nucleophile (Fig. 10 a). Upon substrate binding, the previously bridged hydroxide shifts to coordinate predominately with one metal ion. Enzymes believed to function through such a mechanism include a purple acid phosphatase [79], DNA polymerase I [80], inositol monophosphatase [81],fructose-1,6-bisphosphatase [82], Bam HI [83], and ribozymes [63]. 

Fructose 2,6-bisphosphate (Fru-2,6-bP) plays an important part in carbohydrate metabolism. This metabolite is formed in small quantities from fructose 6-phosphate and has purely regulatory functions. It stimulates glycolysis by allosteric activation of phosphofructokinase and inhibits gluconeogenesis by inhibition of fructose 1,6-bisphosphatase. 

Schtile T, Rose M, Entian KD, Thumm M, Wolf DH (2000) UbcSp functions in catabolite degradation of fructose-1,6-bisphosphatase in yeast. EMBO J 19 2161-2167... 

As with other biochemical pathways, hormones affect gluconeogenesis by altering the concentrations of allosteric effectors and the rate key enzymes are synthesized. As mentioned previously, glucagon depresses the synthesis of fructose-2,6-bisphosphate, activating the phosphatase function of PFK-2. The lowered concentration of fructose-2,6-bisphosphate reduces activation of PFK-1 and releases the inhibition of fructose-1,6-bisphosphatase. 

Fip.l. Binding of I-chloroplast fructose-1.6-bisphosphatase to Triton X-114 as a function of detergent concentration. I-chloroplast fructose-1.6-hisphosphatase was incubated at 0 C for 30 minutes in a solution of 40 mM Tris-HCl buffer (pH 7.9) containing Triton X-114, as indicated. Phase separation of Triton X-114 and estimation of radioactivity was carried out as described under Experimental Procedures. 

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