Effect of extra- and intra-mitochondrial calcium on citrulline synthesis

Summary A quantitative relationship between rat liver mitochondrial matrix free Ca²⁺ (Ca²⁺]_m) and citrullinogenesis has been observed. Maximum citrulline synthesis occurred at 100 to 200nM Ca²⁺]_m; higher Ca²⁺]_m caused inhibition. When Ca²⁺]_m was decreased to below 50nM, by addition of A23187 and EGTA, inhibition also occurred. By incubating mitochondria with ruthenium red (Ca²⁺]_m = 200nM) prior to addition of extramitochondrial free Ca²⁺ (Ca²⁺]_o) it was found that high external Ca²⁺ (800nM) did not inhibit citrulline synthesis thus demonstrating that Ca2+]m, not Ca²⁺]_o was controlling citrullinogenesis.