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Title: Mechanistic studies of porphobilinogen synthase
Author: Goodwin, C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2003
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Porphobilinogen Synthase (PBGS) is a key enzyme involved in tetrapyrrole biosynthesis. The enzyme catalyses the condensation of two molecules of 5-aminolevulinic acid (1) (ALA) to give the pyrrole porphobilinogen (2) (PBG) and is believed to exist in all organisms. This thesis describes mechanistic studies carried out on PBGS from bovine liver and Bacillus subtilis. Stereospecifically deuteriated ALA, (S)-[3-D1]ALA 3S, and (R)-[3-D1]ALA 3R, were synthesised in 13 steps from (S)- and (R)-glutamic acid respectively. The kinetics of PBGS from both bovine liver and B. subtilis were measured with the two substrates and kinetic isotope effects on Vmax observed. For both species of PBGS, a significantly larger kinetic isotope effect on Vmax was observed with 3R than 3S, suggesting that the first deprotonation at C3 of ALA is of the pro-R hydrogen. Based on available crystal structures of PBGSs a modified mechanism has been proposed. The potent inhibitor 3-acetyl-4-oxoheptane-1,7-dioc acid (4) (AOHD) was synthesised containing 13C labels at either C8 or C4. The inhibitor was irreversibly bound to the enzyme from B. subtilis by reduction of the Schiff’s base with sodium borohydride. Using 13C NMR, attempts were made to observe the bound AOHD and determine which ketone formed a Schiff’s base to a lysine in the active site. Studies were made towards the synthesis of novel compounds 5 and 6, as potential inhibitors of PBGS. The synthetic routes utilised were based on those used to synthesise the stereospecifically deuteriated ALAs 3S and 3R.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available