Heme content and breakdown in developing chloroplasts

Conference · Tue May 01 04:00:00 EDT 1990 · Plant Physiology, Supplement; (USA)

OSTI ID:5628979

Thomas, J; Weinstein, J D ^[1]

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1. Clemson Univ., SC (USA)

Heme regulates tetrapyrrole biosynthesis in plants by inhibition of {delta}-aminolevulinic acid (ALA) synthesis, product inhibition of heme synthesis, and possibly other mechanisms. Plastid heme levels may be modulated by heme synthesis, breakdown and/or efflux. Heme breakdown may be catalyzed by a chloroplast localized heme oxygenase. Chloroplasts isolated from greening cucumber cotyledons were incubated in the presence or absence of various components thought to modulate heme breakdown. Following the incubations, the chloroplasts were broken (freeze-thaw) and then supplemented with horseradish peroxidase apoenzyme. The reconstituted peroxidase activity was used to determine the amount of free heme remaining (Thomas Weinstein (1989) Plant Physiol. 89S: 74). Chloroplasts, freshly isolated from seedlings greened for 16 hours, contained approximately 37 pmol heme/mg protein. When chloroplasts were incubated with 5 mM NADPH for 30 min, the endogenous heme dropped to unmeasurable levels. Exogenous heme was also broken down when NADPH was included in the incubation. Heme levels could be increased by the inclusion of 50 {mu}M ALA and/or p-hydroxymercuribenzoate. The increase due to exogenous ALA was blocked by levulinic acid, an inhibitor of ALA utilization. NADPH-dependent heme breakdown acid was inhibited by p-hydroxymercuribenzoate.

• OSTI ID: 5628979
• Report Number(s): CONF-9007196--
• Conference Information: Journal Name: Plant Physiology, Supplement; (USA) Journal Volume: 93:1
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
AMINOLEVULINIC ACID
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHLOROPLASTS
CUCUMBERS
FOOD
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MAGNOLIOPHYTA
MAGNOLIOPSIDA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PLANTS
PORPHYRINS
REACTION KINETICS
SEEDLINGS
VEGETABLES