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Title: Measurement of heme efflux and heme content in isolated developing chloroplasts. [Cucumis sativus, cv. Sumter]

Hemes destined for cytosolic hemoproteins must originate in one of the cellular compartments which have the capacity for heme synthesis, namely the chloroplast or the mitochondria. Since developing chloroplasts from greening cucumber (Cucumis sativus, cv. Sumter) cotyledons are known to contain complete heme and chlorophyll biosynthetic pathways, they were tested for their capacity export hemes. Picomole quantities of heme were measured by reconstitution of the heme with apo-peroxidase and subsequent determination of peroxidase activity. The assay method was sensitive (as little as 0.7 picomole of heme could be detected in a volume of 100 microliters) and was linear with heme concentration. When intact plastids were incubated with apo-peroxidase, a steady-state rate of efflux between 0.12 and 0.45 picomole heme/minute/milligram plastid protein was measured. The efflux rate was not due to plastid breakage and could be enhanced by incubating with the heme precursor, {delta}-aminolevulinic acid. Cold acetone extraction removed 47 {plus minus} 17 picomoles heme/milligram plastid protein from the total b-type heme pool in the chloroplasts (166 {plus minus} 9 picomoles heme/milligram protein, by acid-acetone extraction). The reconstitution technique provided a similar estimate of readily exchangeable heme in the plastid, 37 {plus minus} 8 picomoles heme/milligram protein (or 6 micromolar inmore » the plastids). These values may be indicative of a free heme pool which exists in the chloroplast.« less
Authors:
;  [1]
  1. (Clemson Univ., SC (USA))
Publication Date:
OSTI Identifier:
5626595
Resource Type:
Journal Article
Resource Relation:
Journal Name: Plant Physiology; (USA); Journal Volume: 94:3
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; CUCUMBERS; PHYSIOLOGY; HEME; MEASURING METHODS; BIOLOGICAL PATHWAYS; CHLOROPLASTS; ENZYME ACTIVITY; PEROXIDASES; CARBOXYLIC ACIDS; CELL CONSTITUENTS; ENZYMES; FOOD; HETEROCYCLIC ACIDS; HETEROCYCLIC COMPOUNDS; MAGNOLIOPHYTA; MAGNOLIOPSIDA; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; OXIDOREDUCTASES; PIGMENTS; PLANTS; PORPHYRINS; VEGETABLES 551000* -- Physiological Systems