The conversion of citrate into cis-aconitate and isocitrate in the presence of aconitase

Martius &Lynen (1950) andFriedrich-Freksa &Martius (1951) have expressed doubts on the inter- mediary formation of ci-aconitate in the aconitase system because a study of the kinetics of the con- version of citrate into isocitrate failed to show a lag period.The authors argue that if the conversion followed the original scheme of Martius (1937) citrate =cs-aconitate i8ocitrate the rate of formation of isocitrate should gradually rise until the optimal concentration range of ci- aconitate was built up, and they conclude from the absence of a lag period in their experiments that the interconversion of citrate and isocitrate does not necessitate the formation of c8-aconitate.The experiments reported in this paper were designed to re-investigate the question of the existence of a lag period in the aconitate system.Dilute heart-muscle aconitase preparations were mixed with citrate, and the time course of the formation of aconitate and i8ocitrate was measured at 25°.Dilution and a relatively low temperature draws out the time curve and thus favours the detection of a lag period.