G. Popperl et al., MAGNESIUM CHELATASE OF HORDEUM-VULGARE L IS NOT ACTIVATED BY LIGHT BUT INHIBITED BY PHEOPHORBIDE, Zeitschrift fur Naturforschung. C, A journal of biosciences, 52(3-4), 1997, pp. 144-152
The enzyme activity of magnesium chelatase was determined in intact et
ioplasts of barley (Hordeum vulgare L.) seedlings. Irradiation of isol
ated plastids with white light for 15 min does not lead to any activat
ion of the enzyme but to a decrease in activity, especially in etiopla
sts. The enzyme was inhibited by chlorophyllide and zinc pheophorbide
only to a certain extent. Strong inhibition was observed with the meta
l-free pheophorbide (K-i = 0.92 mu M) but not with pheophytin or chlor
ophyll. Penetration of chlorophyllide through the envelope membrane wa
s confirmed by the chlorophyll synthase reaction that occurs in the in
ner membranes of etioplasts and chloroplasts. The possible role of inh
ibition of magnesium chelatase by pheophorbide in senescent leaves and
tetrapyrrole transport across the plastid envelope are discussed.