Abstract
Abstract— A method for a partial purification of ATP:citrate oxaloacetate lyase from rat brain is described.The Lineweaver–Burk plots of velocity vs citrate concentration are biphasic in the presence of fixed concentrations of MgCl2. Therefore two values of Km, corresponding to low and high concentrations of citrate, can be determined. When MgCl2 is added in equimolar concentrations with citrate, a monophasic plot with one Km of 0.13 mm is obtained. The Km value for MgATP2‐ was independent of citrate concentration, being equal to 0.40–0.43 mm. The Km for CoA was 0.0007 mm.ADP and Pi are competitive inhibitors with respect to ATP. Ki for MgADP− is equal to 0.13 mm. dl‐isocitrate and cis‐aconitate are partially competitive inhibitors with respect to citrate with Ki values of 5.8 and 4.8 mm, respectively. α‐Ketoglutarate and pyruvate are noncompetitive inhibitors with respect to ATP and citrate, with Ki values equal to 9 and 45 mm, respectively.The physiological significance of these effectors for the regulation of citrate lyase activity in brain is discussed.
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