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Title: Studies on s-adenosylmethionine : magnesium-protoporphyrin methyltransferase (EC and related enzymes in euglena gracilis
Author: Ebbon, Jean GreIg
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1969
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S-Adenosylmethionine:magnesium-protoporphyrin methyltransferase (methylating enzyme) has been detected in extracts of light- and dark-grown Euglena gracilis. The activities of this enzyme and of aminolnevulate dehydratase were found to be greater in light-grown cells than dark-grown cells. The methylating enzyme has been detected in purified chloroplasts, in light-grown and dark-grown cells, the enzymic activity being mainly found in particulate fractions. However, about 15-20% was found in the particle-free supernatant. The Chloronlast methylating enzyme has been solubilised by buffer extraction of an acetone dried powder of chloroplasts or chloroplasts extracted with 90% acetone. Addition of Tween 80 (0.5% v/v) to a chloroplast suspension resulted in an immediate two-fold increase of methylating enzyme activity. Further studies have shown that this is probably due to the Increased solubility of the substrate, magnesium protoporphyrin, in the presence of Tween. Addition of the detergent also caused the solubilisation of the enzyme from the Chloroplast membrane; this and other evidence has indicated that lipid may be involved in binding the enzyme to the chloroplasts. However, the enzyme does not appear to require lipid for activity. The enzyme solubilised from chloroplasts by Tween has been partially purified. Its properties have been investigated. From experiments in which etiolated cells were illuminated in the presence of inhibitors of chloroplast or cytoplasmic protein synthesis it appears that the methylating enzyme is synthesised on cytoplasmic ribosomes. This hypothesis is also compatible with the results of experiments carried out to determine the level and subcellular distribution of the enzyme in cells bleached by the presence of streptomycin or by magnesium deprivation. Attempts to demonstrate aminolaevulic acid synthetase or the incorporation of magnesium into protoporphyrin with extracts of this organism were unsuccessful.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available