Abstract
In characterizing the carbonic anhydrase (CA) found in maize thylakoid membranes, it was observed that the enzyme's activity was inhibited somewhat when the Hill oxidant, ferricyanide, was given in the dark [Stemler, A. (1986) Biochim. Biophys. Acta 850, 97-107]. In the present work, a redox titration of this effect shows that the CA activity is mediated by a component that has a midpoint potential (Em) of about 485 mV at pH 6.5 and a pH dependence of 60 mV/pH. These redox titration characteristics are identical to those of the redox mediator "D480", which modulates formate and bicarbonate binding affinity to photosystem II (PS II). Bicarbonate binds to PS II more readily, and CA activity is higher, when D480 is reduced, whereas both bicarbonate binding and thylakoid-bound CA activity are low when D480 is oxidized in the dark by ferricyanide. Both the low bicarbonate binding affinity and the low CA activity induced by the presence of ferricyanide are reversed by a single saturating flash of light. In contrast, the activity of soluble CA, which is extracted from maize mesophyll cytosol, does not exhibit any redox dependence in the range 400-550 mV. Furthermore, thylakoid-bound CA activity is inhibited by 5 mM ZnCl2 by as much as 75%, whereas the activity of soluble CA shows no significant decrease induced by ZnCl2. Also, at a medium potential of 400 mV, ferricyanide (1 mM) inhibits soluble CA activity by 88% and thylakoid-bound CA activity by only 18%. It is concluded from these results that CA activity observed in thylakoids arises from CA inherent to PS II and is not some form of contamination by soluble CA. Possible roles of CA in PS II reaction mechanisms are discussed.
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Claims 14
Claim · model-written summary
Thylakoid CA activity was mediated by a component with a midpoint potential near 485 mV.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CA activity is mediated by a component that has a midpoint potential (Em) of about 485 mV at pH 6.5 and a pH dependence of 60 mV/pH”
t0“Maize”
Claim · model-written summary
The component showed a pH dependence of 60 mV/pH.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CA activity is mediated by a component that has a midpoint potential (Em) of about 485 mV at pH 6.5 and a pH dependence of 60 mV/pH”
t0“Maize”
Claim · model-written summary
Redox titration characteristics matched D480.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These redox titration characteristics are identical to those of the redox mediator "D480"”
t0“Maize”
Claim · model-written summary
Bicarbonate bound more readily when D480 was reduced.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Bicarbonate binds to PS II more readily, and CA activity is higher, when D480 is reduced”
t0“Maize”
Claim · model-written summary
CA activity was higher when D480 was reduced.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CA activity is higher, when D480 is reduced”
t0“Maize”
Claim · model-written summary
Ferricyanide oxidation in darkness lowered bicarbonate binding and thylakoid CA activity.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“both bicarbonate binding and thylakoid-bound CA activity are low when D480 is oxidized in the dark by ferricyanide”
t0“Maize”
Claim · model-written summary
A saturating flash reversed ferricyanide-induced low bicarbonate binding.
- Treatment
- single saturating flash of lighte0
- Outcome
- low bicarbonate binding affinitye0
- Direction
- reversede0
- Comparator
- presence of ferricyanidee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both the low bicarbonate binding affinity and the low CA activity induced by the presence of ferricyanide are reversed by a single saturating flash of light”
t0“Maize”
Claim · model-written summary
A saturating flash reversed ferricyanide-induced low CA activity.
- Treatment
- single saturating flash of lighte0
- Outcome
- low CA activitye0
- Direction
- reversede0
- Comparator
- presence of ferricyanidee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both the low bicarbonate binding affinity and the low CA activity induced by the presence of ferricyanide are reversed by a single saturating flash of light”
t0“Maize”
Claim · model-written summary
Soluble CA showed no redox dependence from 400 to 550 mV.
- Organ / stage
- mesophyll cytosole0
- Outcome
- redox dependencee0
- Direction
- does not exhibite0
- Value
- 400-550 mVe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soluble CA, which is extracted from maize mesophyll cytosol, does not exhibit any redox dependence in the range 400-550 mV”
Claim · model-written summary
ZnCl2 inhibited thylakoid-bound CA activity by as much as 75%.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“thylakoid-bound CA activity is inhibited by 5 mM ZnCl2 by as much as 75%”
t0“Maize”
Claim · model-written summary
ZnCl2 did not significantly decrease soluble CA activity.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the activity of soluble CA shows no significant decrease induced by ZnCl2”
t0“Maize”
Claim · model-written summary
At 400 mV, ferricyanide inhibited soluble CA activity by 88%.
- Treatment
- ferricyanide (1 mM)e0
- Outcome
- soluble CA activitye0
- Direction
- inhibitse0
- Value
- 88%e0
- Qualifier
- medium potential of 400 mVe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at a medium potential of 400 mV, ferricyanide (1 mM) inhibits soluble CA activity by 88%”
t0“Maize”
Claim · model-written summary
At 400 mV, ferricyanide inhibited thylakoid-bound CA activity by 18%.
- Treatment
- ferricyanide (1 mM)e0
- Outcome
- thylakoid-bound CA activitye0
- Direction
- inhibitse0
- Value
- 18%e0
- Qualifier
- medium potential of 400 mVe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at a medium potential of 400 mV, ferricyanide (1 mM) inhibits soluble CA activity by 88% and thylakoid-bound CA activity by only 18%”
t0“Maize”
Claim · model-written summary
The authors concluded that thylakoid CA activity originates from CA inherent to PS II.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CA activity observed in thylakoids arises from CA inherent to PS II and is not some form of contamination by soluble CA”
t0“Maize”
The same questions in other papers
ferricyanide · molecular: metabolites · Zea mays (maize)Positive and negative results
1 in the opposite direction
- positive
light · molecular: metabolites · Zea mays (maize)Positive and negative results
14 papers in the same direction as this paper · 15 in the opposite direction
- negative
- no effect
- no effect
26 papers more in this group
See all 30 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.