Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases.

Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Research Abstract Details 

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Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Abstract Text:

E Behshad,F J Ruzicka,S O Mansoorabadi,D Chen,G H Reed,P A Frey,

The product of yjeK in Escherichia coli is a homologue of lysine 2,3-aminomutase (LAM) from Clostridium subterminale SB4, and both enzymes catalyze the isomerization of (S)- but not (R)-alpha-lysine by radical mechanisms. The turnover number for LAM from E. coli is 5.0 min(-1), 0.1% of the value for clostridial LAM. The reaction of E. coli LAM with (S)-alpha-[3,3,4,4,5,5,6,6-(2)H8]lysine proceeds with a kinetic isotope effect (kH/kD) of 1.4, suggesting that hydrogen transfer is not rate-limiting. The product of the E. coli enzyme is (R)-beta-lysine, the enantiomer of the clostridial product. Beta-lysine-related radicals are observed in the reactions of both enzymes by electron paramagnetic resonance (EPR). The radical in the reaction of clostridial LAM has the (S)-configuration, whereas that in the reaction of E. coli LAM has the (R)-configuration. Moreover, the conformations of the beta-lysine-related radicals at the active sites of E. coli and clostridial LAM are different. The nuclear hyperfine splitting between the C3 hydrogen and the unpaired electron at C2 shows the dihedral angle to be 6 degrees, unlike the value of 77 degrees reported for the analogous radical bound to the clostridial enzyme. Reaction of (S)-4-thialysine produces a substrate-related radical in the steady state of E. coli LAM, as in the action of the clostridial enzyme. While (S)-beta-lysine is not a substrate for E. coli LAM, it undergoes hydrogen abstraction to form an (S)-beta-lysine-related radical with the same stereochemistry of hydrogen transfer from C2 of (S)-beta-lysine to the 5'-deoxyadenosyl radical as in the action of the clostridial enzyme. The resulting beta-lysyl radical has a conformation different from that at the active site of clostridial LAM. All evidence indicates that the opposite stereochemistry displayed by E. coli LAM is determined by the conformation of the lysine side chain in the active site. Stereochemical models for the actions of LAM from C. subterminale and E. coli are presented.

Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Publishing Authors By Initials

E Behshad,FJ Ruzicka,SO Mansoorabadi,D Chen,GH Reed,PA Frey,

For similar natural sciences: chemistry: chemistry, organic: isomerism: stereoisomerism research abstracts see: natural sciences: chemistry: chemistry, organic: isomerism: stereoisomerism research

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Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Journal Published:

PUBLICATION TYPE: Research Support, N.I.H., Extr

Journal: Biochemistry

VOLUME: 45

Page Numbers: 12639-46

Journal Abbreviation: Biochemistry

ISSN: 0006-2960

DAY: 24

MONTH: Oct

YEAR: 2006

Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Information

Number of References:

LANGUAGE: eng

NlmUniqueID: 370623

Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Keywords Mesh Terms:

KEYWORDS: Stereoisomerism

MESH TERMS: metabolism

Chemical & Substance for Abstract: Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases. Information

Substance Name: lysine 2,3-aminomutase

Registry Number: EC 5.4.3.2

Grant and Affiliation Information for Enantiomeric free radicals and enzymatic control of stereochemistry in a radical mechanism: the case of lysine 2,3-aminomutases.

AFFILIATION: Department of Biochemistry, University of Wisconsin, 1710 University Avenue, Madison, Wisconsin 73726, USA.

Country: United States

AGENCY: United States NIGMS

GRANT: T32 GM08293

ACRONYM: GM

MEDLINETA: Biochemistry

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