Free amino acids and nucleic acid content of cell nuclei isolated by a modification of Behrens' technique.

1. Nuclei were prepared from frozen rat liver by a modification of the technique of Behrens, and were studied with regard to the content of free amino acids and nucleic acid. 2. Under rigorously controlled conditions, preparations of nuclei are obtained by the Behrens' method which form a gel in the presence of 5 or 10 per cent NaCl or of water plus a small amount of dilute alkali; whereas when conditions are less rigorously controlled, nuclei are obtained which form no such gel. The property of forming gels with alkali is probably characteristic of all cell nuclei which have not undergone autolysis. 3. Nuclei prepared by the Behrens' technique contain the enzymes arginase, catalase, and esterase in very appreciable concentrations. 4. The free amino acids of the isolated cell nuclei, as well as of other liver cell fractions, have been investigated using the technique of paper chromatography. 5. The chromatographic patterns of the free amino acids of whole cells, ground cytoplasm, and isolated cell nuclei were very similar or identical. A feature of interest in these chromatograms was the faintness or absence of the spots due to a number of the essential amino acids, as compared to the intensities of the spots due to glycine, alanine, and glutamic acid. Glutathione was present in the isolated nuclei as well as in the whole cells. 6. Chromatograms made from hydrolysates of nuclei showed high concentrations of the essential amino acids and were similar to chromatograms of hydrolysates of typical proteins.