5-aminolevulinate dehydratase activity in thylakoid-related structures of etiochloroplasts from radish cotyledons

Abstract

5-Aminolevulinate dehydratase activity was studied in etiochloroplasts purified from radish cotyledons grown for 120 hr under continuous far-red light. The activity was mainly recovered from the stroma of the organelles, as previously observed, but also from the membrane fraction. The bound activity was not altered after incubation in the presence of NaCl or detergents indicating that the enzyme was neither associated with the pelletable fraction by electrostatic forces nor entrapped in lipid vesicles. After separation of prothylakoids and prolamellar bodies on a sucrose gradient, 5-aminolevulinate dehydratase activity and two-thirds of the total protein were observed in prothylakoids. Carotenoids were mainly present in the prolamellar bodies fraction. A few chlorophylls were observed in prothylakoids and prolamellar bodies, indicating that impure fractions were obtained, but that 5-aminolevulinate dehydratase activity was actually bound to thylakoid-related structures.