DOELLER, J.E.*; KRAUS, D.W.: Sulfide-mediated feedback inhibition of endogenous substrate oxidation in Geukensia demissa gill mitochondria?

Gill mitochondria from Geukensia demissa, a marine mussel from high sulfide sediments, exhibit sulfide-supported respiration with an ADP/O ratio near one. In vivo, sulfide-mediated gill oxygen consumption is three times higher than control at the same ciliary beat frequency, consistent with a change in mitochondrial ADP/O ratio from 3 to 1, and suggesting a change in substrate use from endogenous carbon to sulfide. Carbon-supported mitochondrial respiration declined incrementally following successive sulfide additions, suggesting possible inhibition of endogenous substrate oxidation by endproducts of sulfide metabolism. These numerous endproducts include thiosulfate and sulfite. Although thiosulfate alone had little effect on mitochondrial respiration, sulfite appeared to lower both state 3 and state 4 respiration. Therefore, mitochondrial substrate use may be subject to feedback control by sulfide metabolic endproducts. Supported in part by NSF IBN9219658 and IBN9728409.