Identification and Origin of Hemoglobin in a Gymnophallid Metacercaria (Trematoda: Digenea), a Symbiote in the Marine PolychaeteAmphitrite ornata(Annelida: Terebellidae)

Abstract

Unencysted metacercariae belonging to the family Gyrnnophallidae (Trematoda: Digenea) were isolated from the metanephridial sacs of the common marime worm Amphitrite ornata (Polychaeta: Terebellidae). These metacercariae possess an intracellular red pigment that has characteristic absorption spectra for oxygenated, deoxygenated, and carbon monoxide derivatives of hemoglobin when exposed to oxygen, nitrogen, and carbon monoxide, respectively. The hemoglobin, found in all metacercaria tissues, has an oxygen half-saturation (P50) value = 1.1(S.D. = 0.3) mm Hg at 20° C and pH 7.0. The pigment shows cooperative oxygen binding with a Hill coefficient of 2.2 (S.D. = 0.2) and exhibits a significant Bohr effect between pH 6.8 and 7.4. The hemoglobin has a high molecular weight fraction (∼2.5-3 x 106 daltons) and a 16,000 dalton MW fraction. HPLC ion exchange chromatography shows four distinct protein components. The host possesses both vascular extracellular hemoglobin (erythrocruorin) and coelomic cell hemoglobin. The metacercariae ingest host coelomic cell hemoglobin and probably vascular hemoglobin; however, metacercaria tissue hemoglobin is functionally and biochemically distinct from both host hemoglobins, suggesting an independent origin.