Abstract
Irradiation of fully developed green leaves as well as irradiation of isolated chloroplasts causes a rapid, reversible increase in the activity of NADP‐linked phosphoglyceraldehyde dehydrogenase. This increase is closely connected with the functioning of the non‐cyclic electron flow of photosynthesis. It is accompanied by a decrease in the activity of the NAD‐linked enzyme. The experiments presented here show that it is not the kinase but the dehydrogenase which is the rate limiting factor in the over‐all reaction measured up to date. The activation of the “dark‐enzyme” (= basic enzyme) resulting in the “light‐enzyme” (= activated enzyme) is not due to an unspecific reduction of S‐S‐groups in the reactive center. Dithiothreitol only restores the activity lost during the isolation procedure of the chloroplasts. NADPH rather than dithiothreitol causes a specific activation of the basic enzyme. However the basic enzyme must be present in the completely reduced form to undergo maximal activation. Incubation with dithiothreitol and NADPH thus results in an activation rate as high as that caused by light in vivo. Activation of the NADP‐linked dehydrogenase could also be attained by NADPH after its partial purification by ammonium sulfate fractionation. The activation rate by incubation with different concentrations of NADPH shows a sigmoidal type of curve. There are characteristic differences in sensitivity between the activity of the basic enzyme and its ability to be activated at different temperatures between 52°–60°. The results indicate that the action of NADPH may be an allosteric one, causing a transition from a NAD‐ (or possibly a NAD + NADP)‐dependent to a NADP‐dependent form of the enzyme. A diagram for a feed‐forward activation of the NADP‐linked dehydrogenase which possibly takes part in regulation of CO 2 ‐fixation is presented.
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Claims 13
Claim · model-written summary
Irradiation of green leaves or isolated chloroplasts rapidly and reversibly increased NADP-linked phosphoglyceraldehyde dehydrogenase activity.
- Organ / stage
- fully developed green leavese0
- Treatment
- Irradiatione0
- Outcome
- activity of NADP‐linked phosphoglyceraldehyde dehydrogenasee0
- Direction
- increasee0
Not reportedTaxonComparator
Verbatim
e0“Irradiation of fully developed green leaves as well as irradiation of isolated chloroplasts causes a rapid, reversible increase in the activity of NADP‐linked phosphoglyceraldehyde dehydrogenase”
Claim · model-written summary
The increase in NADP-linked enzyme activity was closely connected with non-cyclic photosynthetic electron flow.
Not reportedTaxon
Verbatim
e0“This increase is closely connected with the functioning of the non‐cyclic electron flow of photosynthesis”
Claim · model-written summary
The light-induced increase was accompanied by decreased NAD-linked enzyme activity.
Not reportedTaxon
Verbatim
e0“It is accompanied by a decrease in the activity of the NAD‐linked enzyme”
Claim · model-written summary
Dehydrogenase, rather than kinase, limited the measured overall reaction rate.
Not reportedTaxon
Verbatim
e0“it is not the kinase but the dehydrogenase which is the rate limiting factor in the over‐all reaction measured up to date”
Claim · model-written summary
Dark-enzyme activation to light-enzyme form was not due to nonspecific reduction of reactive-center disulfide groups.
- Outcome
- activation of the “dark‐enzyme”e0
- Qualifier
- not due to an unspecific reduction of S‐S‐groups in the reactive centere0
Not reportedTaxon
Verbatim
e0“The activation of the “dark‐enzyme” (= basic enzyme) resulting in the “light‐enzyme” (= activated enzyme) is not due to an unspecific reduction of S‐S‐groups in the reactive center”
Claim · model-written summary
Dithiothreitol restored only chloroplast isolation-related activity loss.
- Treatment
- Dithiothreitole0
- Outcome
- activity lost during the isolation procedure of the chloroplastse0
- Direction
- restorese0
Not reportedTaxonComparator
Verbatim
e0“Dithiothreitol only restores the activity lost during the isolation procedure of the chloroplasts”
Claim · model-written summary
NADPH specifically activated the basic enzyme.
- Treatment
- NADPHe0
- Outcome
- activation of the basic enzymee0
- Direction
- activatione0
- Comparator
- dithiothreitole0
Not reportedTaxon
Verbatim
e0“NADPH rather than dithiothreitol causes a specific activation of the basic enzyme”
Claim · model-written summary
Maximal activation required the basic enzyme to be fully reduced.
Not reportedTaxon
Verbatim
e0“the basic enzyme must be present in the completely reduced form to undergo maximal activation”
Claim · model-written summary
Dithiothreitol plus NADPH activated the enzyme as strongly as light in vivo.
- Treatment
- dithiothreitol and NADPHe0
- Outcome
- activation ratee0
- Direction
- as high ase0
- Comparator
- light in vivoe0
Not reportedTaxon
Verbatim
e0“Incubation with dithiothreitol and NADPH thus results in an activation rate as high as that caused by light in vivo”
Claim · model-written summary
NADPH activated partially purified NADP-linked dehydrogenase.
- Treatment
- NADPHe0
- Outcome
- Activation of the NADP‐linked dehydrogenasee0
- Direction
- Activatione0
- Qualifier
- after its partial purification by ammonium sulfate fractionatione0
Not reportedTaxonComparator
Verbatim
e0“Activation of the NADP‐linked dehydrogenase could also be attained by NADPH after its partial purification by ammonium sulfate fractionation”
Claim · model-written summary
Activation rate followed a sigmoidal response across NADPH concentrations.
- Treatment
- different concentrations of NADPHe0
- Outcome
- activation ratee0
- Qualifier
- sigmoidal type of curvee0
Not reportedTaxonDirection
Verbatim
e0“The activation rate by incubation with different concentrations of NADPH shows a sigmoidal type of curve”
Claim · model-written summary
Basic-enzyme activity and activation ability differed in temperature sensitivity at 52°–60°.
Not reportedTaxon
Verbatim
e0“There are characteristic differences in sensitivity between the activity of the basic enzyme and its ability to be activated at different temperatures between 52°–60°”
Claim · model-written summary
The authors propose that NADPH acts allosterically to shift the enzyme toward an NADP-dependent form.
- Outcome
- transition from a NAD‐ (or possibly a NAD + NADP)‐dependent to a NADP‐dependent form of the enzymee0
- Qualifier
- action of NADPH may be an allosteric onee0
Not reportedTaxon
Verbatim
e0“the action of NADPH may be an allosteric one, causing a transition from a NAD‐ (or possibly a NAD + NADP)‐dependent to a NADP‐dependent form of the enzyme”