Earthworm bioluminescence: characterization of high specific activity Diplocardia longa luciferase and the reaction it catalyzes.
Diplocardia longa luciferase purified by an improved procedure differs from that first described by Bellisario et al. [Bellisario, R., Spencer, T. E., & Cormier, M. J. (1972) Biochemistry 11, 2256-2266] in having much higher specific activity (40X) and firmly bound, EPR-silent copper. Improved assay conditions suggest that this protein acts as a catalyst in a bioluminescent reaction involving the degradation of 3-(isovalerylamino)-1-hydroxypropane hydroperoxide. This substrate is formed spontaneously on the addition of hydrogen peroxide to D. longa luciferin (3-(isovalerylamino)propanal). The quantum yield of the bioluminescence for this substrate is 3%. Detailed physical and chemical analyses of high specific activity D. longa luciferase indicate that it is a large (300000 daltons), asymmetric (f/fo=1.63, with 0.4 g/g hydration), multisubunit enzyme. It contains carbohydrate (6%), lipid (2%), and copper (up to 4 mol/30000 daltons). The amino acid composition is unusual with 11% by weight of the residues being either proline or hydroxyproline.