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Jaffe EK , Volin M , Myers CB , Abrams WR
5-Chloro 1,4-C-13 Levulinic Acid Modification of Mammalian and Bacterial Porphobilinogen Synthase Suggests an Active-Site Containing 2 Zn(Ii)
Biochemistry. 1994 Sep 27;33(38) :11554-11562
Abstract5-Chloro[1,4-C-13]levulinic acid ([1,4-C-13]CLA) is an active site-directed inactivator of porphobilinogen synthase (PBGS). PBGS asymmetrically condenses two molecules of 5-aminolevulinic acid (ALA) which are called A-side ALA and P-side ALA in reference to their fates as the acetyl and propionyl halves of the product. [1,4-C-13]CLA modifies bovine PBGS at the A-side ALA binding site. The C-4 chemical shift indicates an intact keto moiety; the C-1 chemical shift indicates a deprotonated carboxyl group. In contrast, [1,4-C-13]CLA modification of Escherichia coil PBGS is heterogeneous and occurs preferentially at the P-side ALA binding site. The C-1 chemical shifts indicate substantially deprotonated carboxylic acid groups. For one of four observed forms of [1,4-C-13]CLA- modified E. coli PBGS, an analog of the P-side Schiff base is found. Bovine and E. coli PBGS contain two different zincs, Zn- A and Zn-B. Past results placed Zn-A near A-side ALA. [1,4-C- 13]CLA modifies E. coli PBGS at Cys119 or Cys129, which is part of a four-cysteine cluster implicated in binding Zn-B. This result places Zn-B near P-side ALA. E. coli PBGS binds a third type of divalent metal, Mg-C or Mn-C, which is found to have no significant effect on the C-13 NMR spectrum of the [1,4-C- 13]CLA-modified protein.
NotesEnglish Article PJ293 BIOCHEMISTRY-USA