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

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+](m)) it was found that high external Ca2+ (800nM) did not inhibit citrulline synthesis thus demonstrating that [Ca2+](m), not [Ca2+](o) was controlling citrullinogenesis.