@article {454,
	title = {Dehydroalanine-based inhibition of a peptide epimerase from spider venom},
	journal = {Journal of Organic Chemistry},
	volume = {67},
	number = {24},
	year = {2002},
	note = {ISI Document Delivery No.: 620AATimes Cited: 17Cited Reference Count: 42},
	month = {Nov},
	pages = {8389-8394},
	type = {Article},
	abstract = {Ribosomally produced peptides that contain D-amino acids have been isolated from a number of vertebrate and invertebrate sources. In each case, the D-amino acids are introduced by a posttranslational modification of a parent peptide containing only amino acids of the L-configuration. The only known enzyme to catalyze such a reaction is the peptide epimerase (also known as peptide isomerase) from the venom of the funnel web spider, Agelenopsis aperta. This enzyme interconverts two 48-amino-acid-long peptide toxins that differ only by the stereochemistry at a single serine residue. In this paper we report the synthesis and testing of two pentapeptide analogues that contain modified amino acids at the site normally occupied by the substrate serine residue. When the L-chloroalanine-containing peptide 3 was incubated with the epimerase it was converted into the dehydroalanine-containing peptide 4 via an elimination of HCl. The dehydroalanine peptide 4 was independently synthesized and found to act as a potent inhibitor of the epimerase (IC50 = 0.5 muM). These results support a direct deprotonation/reprotonation mechanism in which a carbanionic intermediate is formed. The observed inhibition by 4 can be attributed to the sp(2)-hybridization of the a-carbon in the dehydroalanine unit that mimics the planar geometry of the anionic intermediate.},
	keywords = {ACID, ACTIVE-SITE, ENZYME, GLUTAMATE RACEMASE, GRAMICIDIN-S SYNTHETASE, INFLUENZAE DIAMINOPIMELATE EPIMERASE, INITIATION MODULE PHEATE, MECHANISM, PROLINE RACEMASE, RESIDUES},
	isbn = {0022-3263},
	url = {<Go to ISI>://000179509400011},
	author = {Murkin, A. S. and Tanner, M. E.}
}
@article {4557,
	title = {Catalytic acid/base residues of glutamate racemase},
	journal = {Biochemistry},
	volume = {38},
	number = {13},
	year = {1999},
	note = {ISI Document Delivery No.: 182QZTimes Cited: 43Cited Reference Count: 37},
	month = {Mar},
	pages = {4106-4113},
	type = {Article},
	abstract = {Glutamate racemase is a cofactor-independent enzyme that employs two active-site cysteine residues as acid/base catalysts during the interconversion of glutamate enantiomers, In a given reaction direction, a thiolate from one of the cysteines abstracts the alpha-proton, and the other cysteine thiol delivers a proton to the opposite face of the resulting carbanionic intermediate. This paper reports that the C73S and C184S mutants are still capable of racemizing glutamate with specificity constants about 10(3)-fold lower than those of the wild-type enzyme, A "one-base requiring" reaction, the elimination of water from N-hydroxyglutamate, has been used to deduce which thiol acts as the base for a given enantiomer. With D-N-hydroxyglutamate the C73S mutant is a much poorer catalyst than wild-type enzyme, whereas the C184S mutant is a somewhat better catalyst. This trend was reversed with L-N-hydroxyglutamate, suggesting that Cys73 is responsible for the deprotonation of D-glutamate and Cys184 is responsible for the deprotonation of L-glutamate. In addition, with C73S the V-max/K-M isotope effect on D-glutamate racemization was greater than that seen with wild-type enzyme, whereas the isotope effect with L-glutamate had decreased. The results were reversed with the C184S mutant. This is interpreted as being due to an asymmetry in the free energy profiles that is induced upon mutation, with the deprotonation step involving a serine becoming the more cleanly rate-determining of the two. These results support the above assignment and the notion that a carbanionic intermediate is formed during catalysis.},
	keywords = {BACILLUS-STEAROTHERMOPHILUS, DIAMINOPIMELATE EPIMERASE, ENERGETICS, ESCHERICHIA-COLI, INHIBITOR, IRREVERSIBLE, L-ALANINE, MANDELATE RACEMASE, MECHANISM, PROLINE RACEMASE, PURIFICATION},
	isbn = {0006-2960},
	url = {<Go to ISI>://000079510800031},
	author = {Glavas, S. and Tanner, M. E.}
}
