The magnesium chelation step in chlorophyll biosynthesis
The biogenesis of energy transducing membranes requires the coordinate synthesis of prosthetic groups, proteins and lipids. Two of the major prosthetic groups, chlorophyll and heme, share a common biosynthetic pathway that diverges at the point of metal insertion into protoporphyrin IX. Insertion of iron leads to heme, while insertion of magnesium leads to chlorophyll. The Mg-chelatase from intact cucumber chloroplasts has been characterized with regard to substrate specificity, regulation, ATP requirement, and a requirement for intact chloroplasts. Mg-chelatase was isolated from maize, barley and peas and characterized in order to circumvent the intact chloroplast requirement of cucumber Mg-chelatase. Pea Mg-chelatase activity is higher than cucumber Mg-chelatase activity, and lacks the requirement for intact chloroplasts. Studies on isolated pea Mg-chelatase have shown more cofactors are required for the reaction than are seen with ferrochelatase, indicating a greater opportunity for regulatory control of this pathway. Two of the cofactors are proteins, and there appears to be a requirement for a protease-sensitive component which is outside the outer envelope. We are developing a continuous spectrophotometric assay for Mg-chelatase activity, and an assay for free heme which has shown heme efflux from intact chloroplasts. 18 refs. (MHB)
- Research Organization:
- Clemson Univ., SC (United States). Dept. of Biological Sciences
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG09-89ER13989
- OSTI ID:
- 5109357
- Report Number(s):
- DOE/ER/13989-3; ON: DE92001815
- Country of Publication:
- United States
- Language:
- English
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In vitro assay of the chlorophyll biosynthetic enzyme Mg-chelatase: Resolution of the activity into soluble and membrane-bound fractions
An organelle-free assay for pea chloroplast Mg-chelatase: Resolution of the activity into soluble and membrane bound fractions
Related Subjects
BIOLOGICAL PATHWAYS
REACTION INTERMEDIATES
CHLOROPHYLL
BIOSYNTHESIS
MAGNESIUM
CHELATING AGENTS
ATP
ATP-ASE
BARLEY
BIOCHEMICAL REACTION KINETICS
CUCUMBERS
ENZYME ACTIVITY
ENZYME INHIBITORS
HEME
MAIZE
PHOTOSYNTHETIC MEMBRANES
PISUM
PORPHYRINS
PROGRESS REPORT
ACID ANHYDRASES
ALKALINE EARTH METALS
CARBOXYLIC ACIDS
CEREALS
DOCUMENT TYPES
ELEMENTS
ENZYMES
FOOD
GRAMINEAE
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROLASES
KINETICS
LEGUMINOSAE
LILIOPSIDA
MAGNOLIOPHYTA
MAGNOLIOPSIDA
MEMBRANES
METALS
NUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHOHYDROLASES
PHYTOCHROMES
PIGMENTS
PLANTS
PROTEINS
REACTION KINETICS
SYNTHESIS
VEGETABLES
550200* - Biochemistry
550500 - Metabolism