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Title: Vitamin B12 and folic acid in the synthesis of methionine by micro-organisms
Author: Guest, J. R.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1960
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Nutritional and isotopic tracer studies with both animals and micro-organisms have shown that vitamin B12 and folic acid are concerned in the biosynthesis of methionine from homocysteine and a source of C1-units (e.g. serine or formaldehyde). Using washed suspensions of E. coli serine has been found to be the most important C1-donor and requirements for p-aminobenzoic acid and cobalamin were also demonstrated with the corresponding auxotrophic strains. Soluble extracts of acetone-dried E. coli PA15 (a serine or glycine requiring strain) catalysed the formation of methionine from serine and homocysteine when an extract of the heated organism (EHC) served as the source of folic acid cofactor; no requirement for cobalamin was observed. However replacement of the SHC by tetrahydropteroylglutamic acid (PtH4G) was not possible unless the enzymic extract was prepared from acetone-dried powders of organisms which had first been grown in the presence of added cobalamin. A heat-labile, non-diffusible factor (X) was partially-purified from the extract of cobalamin-grown organisms and this factor (X) were essential for the utilisation of PtH4G as a cofactor for the synthesis of methionine by extracts of acetone-dried organisms grown without added cobalamin. The synthesis of methionine by ultrasonic extracts of E. coli 121/176 (a cobalamin or methionine requiring strain, grown with methionine} was on the other hand dependent upon the presence of cobalamin in the reaction mixture with either EHO or PtH4G as the cofactor for C1-transfer. The object of this work was to investigate further the complexities of the methylation of homocysteine by ultrasonic extracts of Escherichia coli with particular regard to the functions of folic acid and cobalamin.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available