MASS-SPECTROMETRIC DETERMINATION OF THE RADICAL SCISSION SITE IN THE ANAEROBIC RIBONUCLEOTIDE REDUCTASE OF ESCHERICHIA-COLI

Active anaerobic ribonucleotide reductase from Escherichia coli contai ns an oxygen sensitive organic radical, proposed to reside on glycine- 681 at the C-terminal end of the polypeptide chain. Exposure of the ra dical containing enzyme to oxygen results in cleavage of the molecule at the site of the hypothetical radical. We determined by mass spectro metry the size of the complete and the C-terminal-processed polypeptid es. The difference in size between the two molecules shows that cleava ge occurs at the N-terminal side of glycine-681, demonstrating that th e organic radical is indeed located on this amino acid residue. (C) 19 95 Academic Press, Inc.