TERMINAL ENZYMES OF HEME-BIOSYNTHESIS IN THE PLANT PLASMA-MEMBRANE

Purified plasma membrane fractions from barley leaf exhibited activiti es of ferrochelatase and iron reductase, two of the terminal enzymes i n heme biosynthesis. These activities were also present in purified ba rley leaf plastid and mitochondrial fractions. The plasma membrane fra ctions were shown to be free from contamination with plastid and mitoc hondrial membrane markers. Previous studies had demonstrated that barl ey plasma membranes exhibited activity for converting protoporphyrinog en to protoporphyrin, another late step in heme synthesis. The presenc e of the terminal steps of heme synthesis in the plant plasma membrane is compatible with the hypothesis that late heme precursors such as p rotoporphyrin or protoporphyrinogen synthesized in the chloroplast can be exported and converted to heme within the plasma membrane for subs equent incorporation into plasma membrane hemoproteins. (C) 1995 Acade mic Press, Inc.