Earthworm bioluminescence: Characterization of high specific activity Diplocardia longa luciferase and the reaction it catalyzes

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Abstract
D. longa luciferase purified by an improved procedure differs from that 1st described by Bellisario et al. in having much higher specific activity (40 .times.) and firmly bound, EPR-silent Cu. 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 (300,000 daltons), asymmetric (f/f0 = 1.63, with 0.4 g/g hydration), multisubunit enzyme. It contains carbohydrate (6%), lipid (2%) and Cu (up to 4 mol/300,000 daltons). The amino acid composition is unusual with 11% by weight of the residues being either proline or hydroxyproline.

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