LIGHT ACTIVATION OF SEDOHEPTULOSE-1,7-BISPHOSPHATASE BY A RECONSTITUTED THYLAKOID SYSTEM COMPARED WITH DTT ACTIVATION - EVIDENCE FOR PROTEIN ENZYME INTERACTIONS

A reconstituted thylakoid system including isolated spinach thylakoids, ferredoxin, thioredoxin and ferredoxin-thioredoxin reductase (FTR) was shown to provide sufficient electron transfer flow to mediate photoactivation of sedoheptulose-1,7-bisphosphatase (SBPase). Progress curves were linear under these conditions, in contrast to the lags observed after reductive activation of SBPase by DTT. In this case the lag was suppressed in the presence of ferredoxin + thioredoxin, and addition of FTR to this incubation medium resulted in a substantial increase of SBPase activity. Evidence obtained from gel filtration suggests that during the activation process, incubation of SBPase with ferredoxin, thioredoxin and FTR resulted in enzyme-protein or enzyme-enzyme associations and/or conformational changes.