Studies on human heart citrate synthase.

Citrate synthase from human heart was purified by affinity chromatography with Sepharose-ATP. The molecular weight (100,000) and the presence of two presumably identical subunits do not differ from other mammalian citrate synthases. However, the kinetics constants and immunologic characteristics of the enzyme differed from other mammalian citrate synthases. The Km values for acetyl-CoA (0.4 microM) and oxaloacetate (0.25 microM) were about an order of magnitude lower than those previously found for other mammalian (and eucaryotic) citrate synthases. The kinetics constants for the reverse reaction Km for citrate (420 microM) and CoA (70 microM), were of similar magnitude to the values for other mammals. Anti-human heart antiserum developed a single precipitin line in an Ouchterlony plate against a heart extract, no precipitin line with brain, and a precipitin line with spurs against liver and kidney extract. Following myocardial infarction in men, the enzyme appeared in peripheral blood rarely and in low concentration in contrast with earlier experiences with experimental infarction in dogs.