SULFIDE MAY DIRECTLY MODIFY CYTOPLASMIC HEMOGLOBIN DEOXYGENATION IN SOLEMYA-REIDI GILLS

The clam Solemya reidi, which survives in sulfide-rich sediments, hous es intracellular sulfide-oxidizing bacteria as symbionts in its gills, The gill bacteriocytes also contain a high concentration of cytoplasm ic hemoglobin, Although the in situ hemoglobin optical spectrum was no t altered in the presence of hydrogen sulfide, hemoglobin deoxygenatio n was significantly slowed and incomplete when sulfide was present, A sulfide-mediated decrease in oxygen consumption rate, a shift in intra cellular pH or the conversion of hemoglobin to an unusual derivative c ould all slow in situ hemoglobin deoxygenation, However, under low sul fide levels at which deoxygenation is incomplete, oxygen consumption r ate was not inhibited, intracellular pH decreased by less than 0.1 uni ts and the only hemoglobin derivatives present were deoxyhemoglobin an d oxyhemoglobin. These results and preliminary measurements of the iso lated gill hemoglobin dissociation rate constants suggest that sulfide or a rapidly formed oxidation product may directly influence the rate of Solemya reidi gill hemoglobin deoxygenation.