Heme content in developing chloroplasts

Conference · Wed May 01 04:00:00 EDT 1991 · Plant Physiology, Supplement; (United States)

OSTI ID:5600940

Thomas, J; Weinstein, J D ^[1]

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1. Clemson Univ., SC (United States)

Heme regulates tetrapyrrole biosynthesis by inhibition of {delta}-aminolevulinic acid synthesis, product inhibition of heme synthesis, and possibly other mechanisms. Determination of the physiological relevance of this inhibition requires a sensitive measurement which can distinguish regulatory free heme from heme which is an integral part of functional hemoproteins. A preliminary estimate was provided by reconstituting peroxidase activity from apo-peroxidase and the heme contained in broken plastids. However, subsequent experiments have suggested that this initial estimate was too large due to reconstitution of apo-peroxidase with heme from functional hemoproteins (i.e. heme stealing). The authors have now refined the measurement techniques to greatly reduce the extent of this heme stealing. Incubation of broken plastids with apo-peroxidase at 10C resolves the kinetics of reconstitution into two components. A fast component levels off after 100 min, and a slow component increases linearly for up to 6 hours. They believe that the heme which reconstitutes during the fast phase represents free heme, and the linear slow component represents heme stealing. In support of this theory, incubation at 15C increases the rate of both components. However, extrapolation to zero time of the slow components of the 10C and 15C time courses results in equivalent amounts of heme. Based on this kinetic differentiation between free heme and hemoprotein heme, chloroplasts isolated from cucumber cotyledons after 30 h of greening contain substantially greater amounts of free heme than etioplasts.

• OSTI ID: 5600940
• Report Number(s): CONF-9107184--
• Conference Information: Journal Name: Plant Physiology, Supplement; (United States) Journal Volume: 96:1
• Country of Publication: United States
• Language: English

Related Subjects

551000* -- Physiological Systems
59 BASIC BIOLOGICAL SCIENCES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL FUNCTIONS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHLOROPLASTS
CUCUMBERS
ENZYME ACTIVITY
ENZYMES
FOOD
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MAGNOLIOPHYTA
MAGNOLIOPSIDA
MEASURING METHODS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDOREDUCTASES
PEROXIDASES
PHYSIOLOGY
PIGMENTS
PLANTS
PORPHYRINS
PROTEINS
REACTION KINETICS
TEMPERATURE EFFECTS
VEGETABLES