Lumazine protein from the bioluminescent bacterium Photobacterium phosphoreum. Purification and characterization.

Lumazine protein, a novel protein containing 6,7-dimethyl-8-ribityllumazine as a bound prosthetic group, is one of the several major proteins produced by the bioluminescent bacteria, Photobacterium phosphoreum. purification to complete homogeneity from cell extracts is achieved in six steps. Lumazine protein is a near spherical, monomeric protein of average molecular weight 20,000; in amino acid composition it is acidic with two isoelectric isomers, pI 4.9 and 5.0, and is hydrophilic (974 cal/residue) with single methionine and tryptophan residues and two accessible cysteines. It contains no carbohydrate. Reaction of the cysteines with dithionitrobenzoic acid results in quenching of the bound lumazine fluorescence but is otherwise reversible. Estimates of protein by dry weight results in a mole ratio of one bound lumazine group per protein.