Abstract
Protein modulase and ferredoxin/thioredoxin reductase are soluble proteins that have been suggested to catalyze the light-dependent modulation of enzyme activity in the stromal compartment of the chloroplast. Protein modulase is active in vitro without additional ferredoxin and thioredoxin, whereas ferredoxin/thioredoxin reductase requires additional ferredoxin and thioredoxin. We hypothesize that protein modulase is a complex protein composed of ferredoxin/thioredoxin reductase, ferredoxin, and thioredoxin. In reconstituted chloroplast systems, antiserum directed against ferredoxin, at concentrations sufficient to inhibit the photoreduction of NADP, had no effect on light modulation. Antiserum directed against thioredoxin gave variable results: one batch of polyclonal antibodies inhibited light modulation, another was stimulatory, and another was without effect. These results suggest that the ferredoxin and thioredoxin active in light modulation are not free in solution. Furthermore, molecular sieve chromatography of stromal proteins results in the elution of four species that catalyze light modulation. Based on whether or not ferredoxin and/or thioredoxin must be added for activity, these four species have been tentatively identified as protein modulase, a complex of ferredoxin/thioredoxin reductase and ferredoxin, a complex of ferredoxin/thioredoxin reductase and thioredoxin, and ferredoxin/thioredoxin reductase. That is, the four correspond to all the possible combinations of ferredoxin, ferredoxin/thioredoxin reductase, and thioredoxin. We suggest that buffer ionic strength affects the interactions among these proteins and in part determines the fate of the protein modulase complex in vitro.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.