WOODWARDS-REAGENT-K REACTS WITH HISTIDINE AND CYSTEINE RESIDUES IN ESCHERICHIA-COLI AND SACCHAROMYCES-CEREVISIAE PHOSPHOENOLPYRUVATE CARBOXYKINASES

The reaction of Woordward's reagent K (WRK) with model amino acids and proteins has been analyzed. Our results indicate that WRK forms 340-n m-absorbing adducts with sulfhydryl- and imidazol-containing compounds , but not with carboxylic acid derivatives, in agreement with Llamas e t al. [(1986), J. Am. Chem. Sec. 108, 5543-5548], but not with Sinha a nd Brewer [(1985), Anal. Biochem. 151, 327-333]. The chemical modifica tion of Escherichia coli and Saccharomyces cerevisiae phosphoenolpyruv ate carboxykinases with WRK leads to an increase in the absorption at 340 nm, and we have demonstrated its reaction with His and Cys residue s in these proteins. These results caution against claims of glutamic or aspartic acid modification by WRK based on the absorption at 340 nm of protein-WRK adducts.