Modeling of Alternative Pathways of Electron Transport to Photosystem I in Isolated Thylakoids

Modeling of Alternative Pathways of Electron Transport to Photosystem I in Isolated Thylakoids Kinetics of dark decay of absorbance changes at 830 nm (ΔА830) was examined in thylakoids isolated from leaves of pea seedlings at various concentrations of exogenous NADPH or NADH. Absorbance changes were induced by far-red light to avoid electron donation from photosystem II. In the presence of either biological reductant, the kinetics of ΔА830 decay reflecting dark reduction of Р700+, the primary electron donor of photosystem I, was fitted by a single exponential term. The rate of Р700+ reduction increased with the rise in the concentration of both NADPH and NADH. The values of K M and V max for Р700+ reduction estimated from concentration dependences were 105 ± 21 μM and 0.32/s for NADPH or 21 ± 8 μM and 0.12/s for NADH. The rate of P700+ reduction by either NADPH or NADH significantly increased in the presence of rotenone, a specific inhibitor of chloroplast reductase. The value of V max was changed only in the presence of rotenone, whereas K m was practically unaffected. Unlike the chloroplasts of intact leaves, the only enzyme mediating the input of reducing equivalents from NADPH or NADH to the electron transport chain was concluded to be present in thylakoids. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Russian Journal of Plant Physiology Springer Journals

Modeling of Alternative Pathways of Electron Transport to Photosystem I in Isolated Thylakoids

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Publisher
Kluwer Academic Publishers-Plenum Publishers
Copyright
Copyright © 2004 by MAIK “Nauka/Interperiodica”
Subject
Life Sciences; Plant Sciences
ISSN
1021-4437
eISSN
1608-3407
D.O.I.
10.1023/B:RUPP.0000040740.72975.c2
Publisher site
See Article on Publisher Site

Abstract

Kinetics of dark decay of absorbance changes at 830 nm (ΔА830) was examined in thylakoids isolated from leaves of pea seedlings at various concentrations of exogenous NADPH or NADH. Absorbance changes were induced by far-red light to avoid electron donation from photosystem II. In the presence of either biological reductant, the kinetics of ΔА830 decay reflecting dark reduction of Р700+, the primary electron donor of photosystem I, was fitted by a single exponential term. The rate of Р700+ reduction increased with the rise in the concentration of both NADPH and NADH. The values of K M and V max for Р700+ reduction estimated from concentration dependences were 105 ± 21 μM and 0.32/s for NADPH or 21 ± 8 μM and 0.12/s for NADH. The rate of P700+ reduction by either NADPH or NADH significantly increased in the presence of rotenone, a specific inhibitor of chloroplast reductase. The value of V max was changed only in the presence of rotenone, whereas K m was practically unaffected. Unlike the chloroplasts of intact leaves, the only enzyme mediating the input of reducing equivalents from NADPH or NADH to the electron transport chain was concluded to be present in thylakoids.

Journal

Russian Journal of Plant PhysiologySpringer Journals

Published: Dec 22, 2004

References

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