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Ultracentrifugation studies show that, at concentrations of about 0.1 mM the aspartate aminotransferase of pig heart muscle does not dissociate into subunits either in 6 M guanidine hydrochloride, pH 7.5, or 8 M urea solution, pH 7.5. On prolonged treatment (8 weeks, 0°) with urea, however, complete dissociation occurs and the measured value of the molecular weight drops to approx. 40,000. The protein so obtained is enzymically inactive and migrates on electrophoresis in starch gel at pH 8.0 as a single, fast-moving band. Gel filtration experiments show that the holoenzyme (pyridoxal form) partly dissociates into two subunits at a concentration of about 3 nM. The specific activity of the enzyme does not change in this region; the monomer and dimer have, therefore, the same catalytic activity per mole of co factor. The apoenzyme ks unstable at high dilution and its dissociation has not been directly demonstrated by gel filtration. However, indirect evidence obtained from a study of the kinetics of its recombination with cofactor suggests that dissociation occurs at a concentration of about 50 nM. [ABSTRACT FROM AUTHOR]

Convenient methods for the purification of the soluble aspartate aminotransferase from pig heart muscle are described. The enzyme obtained is homogeneous in the ultracentrifuge and to starch gel electrophoresis at about pH 9.0. At lower pH, as first described by Fasella et. al. [1], a number of electrophoretically distinct species can be detected. Some of the properties of these are reported. The currently accepted value of the molecular weight of the enzyme is incorrect: ultracentrifuge studies gave a value of 78,600 ± 2,400 (23 determinations). Gel filtration experiments led to a similar value. Titration of apoenzyme with cofactor gives values of the equivalent weight of the protein which vary with the enzumic specific activity. Extrapolation to the maximum specific activity leads to a value for the equivalent weight of about 40,000. The enzyme has, therefore, two cofactor binding sites. [ABSTRACT FROM AUTHOR]

- Normal urine was examined for substances which inhibited the formation of calcium oxalate, using a separation scheme which involved ultrafiltration, alcohol precipitation, electrophoresis and paper chromatography. The major anionic inhibitors were found to be citric acid, isocitric acid and pyrophosphate. The inhibitory activity of urine and that of an artificial urine having the same concentration of urea, creatinine, sodium, potassium, magnesium, calcium, ammonia, sulphate, chloride, inorganic phosphate, oxalate, citrate, isocitrate and pyrophosphate, and the same pH were identical. This confirmed that urine does not contain an unidentified potent substance which inhibits the formation of calcium oxalate. [ABSTRACT FROM AUTHOR]