Regulation of Magnesium Chelatase Activity during Excessive Accumulation of Porphyrins in Green Barley Leaves

Activity of magnesium chelatase was studied in green barley leaves treated with 5-aminolevulinic acid (ALA). After this treatment, leaves accumulated excessive amounts of porphyrinic precursors of chlorophyll : protoporphyrin IX (PP), magnesium-protoporphyrin IX (MgPP), its monomethyl ester (MgPPE), and protochlorophyllide. The enzyme activity was found to be inversely dependent on the amount of MgPP formed from exogenous ALA. A conclusion was drawn about the existence of a mechanism for the regulation of the enzyme activity in vivo via its inhibition by the reaction product.