Amino acid transport in bivalve mollusc mitochondria: The role of the proton motive force and monovalent cations in proline oxidation by oyster (Crassostrea virginica) gill mitochondria

Abstract

AbstractThe role of the proton motive force (PMF) and significance of the common intracellular monovalent cations (Na+ and K+) in proline oxidation by oyster (Crassostrea virginica) gill mitochondria were examined. Proline was oxidized at moderate rates in the presence of ADP under isosmotic conditions. Oxidation of proline was inhibited by CCCP (carbonyl cyanide m‐chlorophenylhydrazone), an uncoupler of oxidative phosphorylation. Oxidation of pyruvate, but not succinate (each oxidized at moderate rates), was inhibited by CCCP, confirming that the PMF was at least partially dissipated. These data suggest that transport of proline is dependent on some component of the PMF, either the pH gradient or the membrane potential. Less inhibition of proline oxidation by CCCP was achieved at higher proline concentrations suggesting that diffusional penetration may become more important as proline concentrations increase. Oxidation of proline was not substantially affected by reducing concentrations of Na+ or K+ or both Na+ and K+ (Na+ < 9 mM; K+ < 1 mM), suggesting that proline transport does not require an inward chemical gradient of these monovalent cations. Monovalent cations stimulated proline oxidation in the order of the Hofmeister series (Na+ > K+ > choline+). The high rate of oxidation achieved using Na+ is unusual and is probably an adaptation related to the high intracellular Na+ concentrations found in many bivalve molluscs.