Regulation by salt and by krebs cycle metabolites of citrate synthase from an osmoregulator, white shrimp, Penaeus setiferus, and from a non-osmoregulator, sea anemone, Bunedosoma cavernata

Abstract

1. 1. Citrate synthase of the white shrimp, Penaeus setiferus, and of the sea anemone, Bunedosoma cavernata, was partially purified. 2. 2. When reacted in various buffer concentrations, Penaeus citrate synthase demonstrated a distinct peak in catalytic activity in 75 mM potassium phosphate or 100 mM Tris-Cl (pH 7·5). Bunedosoma citrate synthase demonstrated a broad, almost flat profile under these conditions. 3. 3. The apparent Michaelis constant for acetyl coenzyme A was increased about fiftyfold in the Penaeus citrate synthase in the presence of 100 mM potassium phosphate buffer as compared to 20 mM buffer. The K m of Bunedosoma citrate synthase was not markedly affected by changes in buffer concentration. The K m 's for OAA were not greatly affected. 4. 4. Both citrate synthases were inhibited by ATP, NADH and α-KG, and an increase in AcSCoA reduced the inhibitions. 5. 5. The molecular weight of P. setiferus and B. cavernata citrate synthases was estimated by gel filtration to be 100,000 Daltons.