Reaction mechanism of the fructose 2,6-bisphosphatase

Fructose 2,6‐bisphosphate has been claimed to be both a substrate analogue and an allosteric inhibitor of fructose‐1,6‐bisphosphatase. The results reported here show that fructose 2,6‐bisphosphate can be both an inhibitor and an activator of the enzyme, depending on the substrate concentration. This biphasic behaviour at saturating concentrations of substrate can only be due to an allosteric effect. In addition to the mechanistic implication it is possible that this finding may have physiological meaning.

Fructose 1,6-bisphosphatase

Fructose 2,6-bisphosphate

10.1016/0014-5793(84)80126-x

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Citations (16)

Studies on the hysteretic properties of chloroplast fructose-1,6-bisphosphatase.

Journal of Biological Chemistry (1983)

Cecilia M. Hertig R.A. Wolosiuk

Chloroplast fructose-1,6-bisphosphatase hysteresis in response to modifiers was uncovered by carrying out the enzyme assays in two consecutive steps. The activity of chloroplast fructose-1,6-bisphosphatase, assayed at low concentrations of both fructose-1,6-bisphosphatase and Mg2+, was enhanced by preincubating the enzyme with dithiothreitol, thioredoxin f, fructose 1,6-bisphosphate, and Ca2+. In the time-dependent activation process, fructose 1,6-bisphosphate and Ca2+ could be replaced by other sugar biphosphates and Mn2+, respectively. Once activated, chloroplast fructose-1,6-bisphosphatase hydrolyzed fructose 1,6-bisphosphate and sedoheptulose 1,7-bisphosphate in the presence of Mg2+, Mn2+, or Fe2+. The A0.5 for fructose 1,6-bisphosphate (activator) was lowered by reduced thioredoxin f and remained unchanged when Mg2+ was varied during the assay of activity. On the contrary, the S0.5 for fructose 1,6-bisphosphate (substrate) was unaffected by reduced thioredoxin f and depended on the concentration of Mg2+. Ca2+ played a dual role on the activity of chloroplast fructose-1,6-bisphosphatase; it was a component of the concerted activation and an inhibitor in the catalytic step. Provided dithiothreitol was present, the activating effectors were not required to maintain the enzyme in the active form. Considered together these results strongly suggest that the regulation of fructose-1,6-bisphosphatase in chloroplast occurs at two different levels, the activation of the enzyme and the catalysis.

Fructose 1,6-bisphosphatase

Dithiothreitol

Fructose 2,6-bisphosphate

10.1016/s0021-9258(18)33147-8

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Citations (78)

FRUCTOSE-1,6-BISPHOSPHATASE COMPLEX WITH AMP, MAGNESIUM, FRUCTOSE-6-PHOSPHATE AND PHOSPHATE (T-STATE)

Juhui Choe Richard B. Honzatko

Fructose 1,6-bisphosphatase

Magnesium phosphate

10.2210/pdb1eyi/pdb

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