Cofactor requirement of the enzymatic reduction of chlorophyll b to chlorophyll a

摘要

There is only little known about the formation and degradation of chlorophyll b (Chl b). Ito et al. suggested a chlorophyll cycle, in which Chl b is converted to Chl a and vice versa. This chlorophyll cycle can be important for the plants: during acclimation from low light to high light conditions the Chl a to Chl b ratio increases. The reason is either a degradation of Chl b bound by the light harvesting complexes or a direct conversion of this Chl b to Chl a. Secondly, up to now only degradation products of Chl a were found in higher plants and the key enzyme of Chl degradation, pheophorbide oxygenase, accepts only pheophorbide a (Pheide a). As a consequence, a separate degradation pathway for Chl b must exist in high plants or Chl b must be reduced to Chl a before the action of Mg-dechelatase. The reduction of Chl b to Chl a could be observed in vitro by addition of the chlorophyllide b (Chlide b) analogon zinc pheophorbide b (ZnPheide b) to isolated etioplasts of barley. The cofactors of this two-step reduction of a formyl group to a methyl group are described here.