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Title: Mechanistic studies on biotin biosynthesis
Author: McPherson, Michael J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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This thesis describes studies on the last two enzymes on the biotin biosynthetic pathway. The penultimate enzyme, dethiobiotin synthetase (DTBS), catalyses the ureido ring closure of dethiobiotin from (7R,8S)-7,8-diaminononanoate (DAPA), carbon dioxide and ATP. The final step, catalysed by biotin synthase, involves the chemically difficult insertion of sulphur into the unacativated carbon skeleton of dethiobiotin to yield biotin. A range of analogues of DAPA differing in chain length and C-8 substitution were synthesised and found to act as slow substrates of DTBS. Steady-state kinetic and binding parameters were evaluated for these modified substrates and their relevance to the mechanism of the DTBS reaction is discussed. Crystallographic and modelling studies of one analogue bound in the active site of DTBS suggest that the enzyme may employ an alternative mechanism of ureido ring closure to that of the native substrate. Biotin production was demonstrated in cell-free extracts of an E. coli bioB transformant and the origin of the sulphur atom in biotin was investigated. A novel cysteine desulphurase enzyme, which catalyses the of L-cysteine to give L-alanine and sulphur, was discovered and its possible role in the biotin synthase reaction is discussed. [6,6-2H2]-(±)-dethiobiotin and [6,6-F2]-(±)-dethiobiotin were identified as target compounds in intermediate trapping experiments and as selective biocides. A synthetic route to these compounds was devised and the introduction of label was explored using labelled catalysts and carbonyl transformation chemistry.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available