title: Light modulation of enzyme activity: activation of the light effect mediators by reduction and modulation of enzyme activity by thiol-disulfide exchange.
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.
authors: Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois 60680.
authors: L E
authors: LE
authors: Anderson
authors: S C
authors: SC
authors: Nehrlich
authors: M L
authors: ML
authors: Champigny