The role of pH and magnesium concentration in the light activation of chloroplastic fructose bisphosphatase

Minot, R.; Meunier, Jean‐Claude; Buc, Jean; Ricard, Jacques

doi:10.1016/0014-5793(82)80232-9

Cited by 31 publications

(13 citation statements)

References 7 publications

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“…FBPase is sensitive to alterations of pH ( 19) which could occur at supraoptimal temperatures. The high FBP/Fru6P ratios observed at the supraoptimal temperatures (Table I) indicate that the flux of carbon through the FBPase reaction may also be limited in vivo at higher temperature.…”

Section: E Cmentioning

confidence: 99%

Influences of Leaf Temperature on Photosynthetic Carbon Metabolism in Wheat

Kobza

Edwards²

1987

Plant Physiol.

209

142

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Section: E Cmentioning

confidence: 99%

Influences of Leaf Temperature on Photosynthetic Carbon Metabolism in Wheat

Kobza

Edwards²

1987

Plant Physiol.

209

142

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“…Since the present results bring evidence of a relatively slow pH-dependent equilibrium between two enzymatic states of oxidized phosphatase, a pH jump from 7.5 to 8.8 must produce a lag by following enzyme activity. That is what was observed, as for the reduced enzyme [3]. But the kinetics of the conformational transition was different from that expected to occur by following enzyme activity (time constants were 9.63 x s-l and 1.6 x lo-' s-l respectively).…”

Section: Discussionmentioning

confidence: 44%

“…The enzyme exists in two states: one oxidized and one reduced [2]. The two forms are active but in vivo, in the light, at pH 8 and with 3 mM Mg2+, only the reduced form is active [3]. Upon illumination the activation of the oxidized enzyme is performed by reduced thioredoxin [4] whereas the reduced enzyme is activated by a pH jump from 7 to 8 concomitant with the dark-light transition [3, 51.…”

mentioning

confidence: 99%

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Effects of pH and fructose 2,6-bisphosphate on oxidized and reduced spinach chloroplastic fructose-1,6-bisphosphatase

1987

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This report describes the effects of pH and fructose 2,6-bisphosphate (an analog of fructose 1,6-bisphosphate) on the activity of oxidized and reduced fructose-l,6-bisphosphatase from spinach chloroplasts. Studies were carried out with either fructose 1,6-bisphosphate, the usual substrate, or sedoheptulose 1,7-bisphosphate, an alternative substrate. The reduction of the oxidized enzyme is achieved by a thiol/disulfide interchange. The pK values relative to each redox form for the same substrate (either fructose 1,6-bisphosphate or sedoheptulose 1,7-bisphosphate) are identical, suggesting the same site for both substrates on the active molecule. The finding that the analog (fructose 2,6-bisphosphate) behaves like a competitive inhibitor for both substrates also favours this hypothesis. The inhibitory effect of this sugar is more important when the enzyme is reduced than when it is oxidized. The shift in the optimum pH observed when [Mg"] was raised is interpreted as a conformational change of oxidized enzyme demonstrated by a change in fluorescence. The reduced and oxidized forms have the same theoretical rates relative to both substrates, but the reduced form has an observed V,,, which is 60% of the theoretical V,,, while that of the oxidized form is only 37% of the theoretical V,,,. The reduced enzyme appears more efficient than the oxidized one in catalysis.

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“…The spontaneous deactivation of NADP-malate dehydrogenase after removal of dithiothreitol and thioredoxin is at variance with what has been shown to occur with chloroplastic fructose bisphosphatase. This enzyme remains active after removing the reductant, and deactivation is explainable by either a steep sensitivity of enzyme to pH changes [11,12], or by electron-transfer to oxidized thioredoxin [13]. Neither of these effects seems to be required to explain deactivation of chloroplastic NADP-malate dehydrogenase in the dark.…”

Section: Discussionmentioning

confidence: 99%