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Studies on the key thiamin diphospha...

Zhang, Sheng.

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Studies on the key thiamin diphosphate-bound enamine intermediate in models and enzymes.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Studies on the key thiamin diphosphate-bound enamine intermediate in models and enzymes./
Author:	Zhang, Sheng.
Description:	194 p.
Notes:	Source: Dissertation Abstracts International, Volume: 64-08, Section: B, page: 3815.
Contained By:	Dissertation Abstracts International64-08B.
Subject:	Chemistry, Biochemistry. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3103612

Studies on the key thiamin diphosphate-bound enamine intermediate in models and enzymes.
Zhang, Sheng.

Studies on the key thiamin diphosphate-bound enamine intermediate in models and enzymes. - 194 p.

Source: Dissertation Abstracts International, Volume: 64-08, Section: B, page: 3815.

Thesis (Ph.D.)--Rutgers The State University of New Jersey - Newark, 2003.

All the thiamin diphosphate (ThDP) dependent enzymes that catalyze the oxidative or non-oxidative decarboxylation of pyruvate share a common mechanism in their first few steps: first, the proton at the C2 position of ThDP is removed to form an ylide intermediate; next, one pyruvate molecule is added to this ylide to form a 2alpha-lactylthiamin diphosphate (LThDP) intermediate; then, the LThDP undergoes decarboxylation leading to a C2alpha-carbanion/enamine intermediate. This enamine is a key intermediate in the pyruvate decarboxylation catalyzed by ThDP dependent enzymes. It can be protonated to form the 2alpha-hydroxyethylthiamin diphosphate (HEThDP) in the non-oxidative pathway, or be oxidized to form the 2-acetylthiamin diphosphate (AcThDP) in the oxidative pathway. The LThDP, HEThDP and AcThDP are stable intermediates, which can be synthesized from ThDP. However, the enamine is not stable and can be readily protonated to form HEThDP under neutral conditions.Subjects--Topical Terms:

1017722
Chemistry, Biochemistry.

Studies on the key thiamin diphosphate-bound enamine intermediate in models and enzymes.
LDR:03975nmm 2200301 4500 001 1860798
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008 130614s2003 eng d
035 $a (UnM)AAI3103612
035 $a AAI3103612
040 $a UnM $c UnM
100 1 $a Zhang, Sheng. $3 1019185
245 1 0 $a Studies on the key thiamin diphosphate-bound enamine intermediate in models and enzymes.
300 $a 194 p.
500 $a Source: Dissertation Abstracts International, Volume: 64-08, Section: B, page: 3815.
500 $a Director: Frank Jordan.
502 $a Thesis (Ph.D.)--Rutgers The State University of New Jersey - Newark, 2003.
520 $a All the thiamin diphosphate (ThDP) dependent enzymes that catalyze the oxidative or non-oxidative decarboxylation of pyruvate share a common mechanism in their first few steps: first, the proton at the C2 position of ThDP is removed to form an ylide intermediate; next, one pyruvate molecule is added to this ylide to form a 2alpha-lactylthiamin diphosphate (LThDP) intermediate; then, the LThDP undergoes decarboxylation leading to a C2alpha-carbanion/enamine intermediate. This enamine is a key intermediate in the pyruvate decarboxylation catalyzed by ThDP dependent enzymes. It can be protonated to form the 2alpha-hydroxyethylthiamin diphosphate (HEThDP) in the non-oxidative pathway, or be oxidized to form the 2-acetylthiamin diphosphate (AcThDP) in the oxidative pathway. The LThDP, HEThDP and AcThDP are stable intermediates, which can be synthesized from ThDP. However, the enamine is not stable and can be readily protonated to form HEThDP under neutral conditions.
520 $a In this thesis, the LThDP and HEThDP were synthesized and used to study the pyruvate decarboxylase component (E1) of the pyruvate dehydrogenase complex (PDHc) from E. coli. The steady-state kinetic experiments showed that E1 could catalyze the following reactions: (1) the deprotonation of HEThDP at the C2alpha position, (2) the release of acetaldehyde from HEThDP; (3) the decarboxylation of LThDP; (4) the release of pyruvate from LThDP. The stopped-flow experiments showed that the E1 accelerates the deprotonation of HEThDP by a factor of 105.
520 $a The enamine generated from the decarboxylation of the 2alpha-lactyl-3,4,5-trimethylthiazolium ion (LTT) in neutral aqueous solution was used to study the oxidation of the enamine by 2,6-dichlorophenolindophenol (DCPIP) and lumiflavin (a model for FAD). The second order rate constant for the reaction of the enamine with DCPIP is 1.2 x 106 s-1M-1 at 30°C. The second order rate constant for the reaction of the enamine with lumiflavin is 7.2 x 105 s-1 M-1 at 30°C. The rate constants of decarboxylation of LTT in THF and CH3CN were also determined. The solvent isotope effects (SIE) for the protonation of the enamine in water or in D2O were also measured.
520 $a The formation of the enamine on yeast pyruvate decarboxylase (YPDC) using 2-oxo-4-pyridin-3-butenoic acids as substrate was studied using the stopped-flow technique. The rate constants of the formation of enamine were measured in the absence of pyruvate (i.e., with unactivated YPDC) and in the presence of 100 mM pyruvamide (i.e., with activated YPDC). A charge transfer band corresponding to the first intermediate, which we believe is similar to the LThDP, was also observed when the 2-oxo-4-(m-pyridin)-3-butenoic acid and 2-oxo-4-(p-pyridin)-3-butenoic acid were used as substrate. This charge transfer band enables us to measure the rate constants of the formation and the decay of the first intermediate. The rate constants obtained in these experiments supported the "alternating site" mechanism previously proposed for this enzyme.
590 $a School code: 0461.
650 4 $a Chemistry, Biochemistry. $3 1017722
650 4 $a Chemistry, Organic. $3 516206
690 $a 0487
690 $a 0490
710 2 0 $a Rutgers The State University of New Jersey - Newark. $3 1017745
773 0 $t Dissertation Abstracts International $g 64-08B.
790 1 0 $a Jordan, Frank, $e advisor
790 $a 0461
791 $a Ph.D.
792 $a 2003
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3103612