Light modulation of enzyme activity: activation of the light effect mediators by reduction and modulation of enzyme activity by thiol-disulfide exchange |
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Authors: | Anderson L E Nehrlich S C Champigny M L |
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Institution: | Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois 60680. |
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Abstract: | Light and dark modulation experiments with pea (Pisum sativum L.) chloroplast stromal fractions pretreated with dithiothreitol (to reduce protein disulfide bonds) or with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) (to block sulfhydryl groups) suggest that light modulation involves thiol-disulfide exchange on the modulatable stromal enzyme protein. Light-dependent reduction of DTNB involves a photosynthetic electron transport chain component located on the reducing side of photosystem I prior to ferredoxin; DTNB may be acting as a light effect mediator substitute. The thylakoid-bound light effect mediator system, then, in its light-activated reduced form probably catalyzes thiol-disulfide exchange reactions on stromal enzymes. |
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