Comparison of chromosomal proteins of mouse primitive teratocarcinoma, liver and L cells

Histone and non-histone proteins of mouse primitive teratocarcinoma cells have been studied by polyacrylamide gel electrophoresis and compared with those of mouse liver and with those of mouse L cells. The electrophoretic patterns and the ratio of histones/ DNA were identical in all cells studied. The electrophoretic patterns of non-histone proteins of teratocarcinoma cells were significantly different from those of the liver and also of the L cells, although more similarities were encountered between the two types of cultured cells.     

AMPHOTERIC COLLOIDS : II. VOLUMETRIC ANALYSIS OF ION-PROTEIN COMPOUNDS; THE SIGNIFICANCE OF THE ISOELECTRIC POINT FOR THE PURIFICATION OF AMPHOTERIC COLLOIDS.

1. It is shown by volumetric analysis that on the alkaline side from its isoelectric point gelatin combines with cations only, but not with anions; that on the more acid side from its isoelectric point it combines only with anions but not with cations; and that at the isoelectric point, pH = 4.7, it combines with neither anion nor cation. This confirms our statement made in a previous paper that gelatin can exist only as an anion on the alkaline side from its isoelectric point and only as a cation on the more acid side of its isoelectric point, and practically as neither anion nor cation at the isoelectric point. 2. Since at the isoelectric point gelatin (and probably amphoteric colloids generally) must give off any ion with which it was combined, the simplest method of obtaining amphoteric colloids approximately free from ionogenic impurities would seem to consist in bringing them to the hydrogen ion concentration characteristic of their isoelectric point (i.e., at which they migrate neither to the cathode nor anode of an electric field). 3. It is shown by volumetric analysis that when gelatin is in combination with a monovalent ion (Ag, Br, CNS), the curve representing the amount of ion-gelatin formed is approximately parallel to the curve for swelling, osmotic pressure, and viscosity. This fact proves that the influence of ions upon these properties is determined by the chemical or stoichiometrical and not by the "colloidal" condition of gelatin. 4. The sharp drop of these curves at the isoelectric point finds its explanation in an equal drop of the water solubility of pure gelatin, which is proved by the formation of a precipitate. It is not yet possible to state whether this drop of the solubility is merely due to lack of ionization of the gelatin or also to the formation of an insoluble tautomeric or polymeric compound of gelatin at the isoelectric point. 5. On account of this sudden drop slight changes in the hydrogen ion concentration have a considerably greater chemical and physical effect in the region of the isoelectric point than at some distance from this point. This fact may be of biological significance since a number of amphoteric colloids in the body seem to have their isoelectric point inside the range of the normal variation of the hydrogen ion concentration of blood, lymph, or cell sap. 6. Our experiments show that while a slight change in the hydrogen ion concentration increases the water solubility of gelatin near the isoelectric point, no increase in the solubility can be produced by treating gelatin at the isoelectric point with any other kind of monovalent or polyvalent ion; a fact apparently not in harmony with the adsorption theory of colloids, but in harmony with a chemical conception of proteins.     

Metal-induced lethality and mutagenesis: possible role of apurinic intermediates

The possible mechanisms by which various metals exert their mutagenic effects were investigated using both chemical and biochemical techniques. Ions of Cu, Ni and Cr enhanced the release of either adenine [Cu(II) and Ni(II)] or guanine [Cr(VI)] from DNA as measured in a chromatography assay, suggesting the possible importance of depurination in metal-induced mutagenesis. Transfection experiments with single-stranded bacteriophage phi X174 DNA indicated that micromolar levels of Cu(II), Cr(III), Cr(VI) and Pt(IV) are capable of causing extensive lethal damage to the phage DNA. In case of Cu(II) and Pt(IV) this damage proved mutagenic for phi X174 am3 after transfection of DNA into SOS-induced spheroplasts. For Cu(II) mutagenesis is likely due to the release of adenine residues from the phage DNA based on the abolishment of mutagenesis by alkali and the observed specificity of the phage revertants. The enhancement of the adenine depurination rate by Cu(II) was estimated to be as high as 10,000-fold.     

Inhibition of RNA Synthesis and the Relationship between Nucleolar and Mitotic Cycles in Zea mays Root Meristems

The relationship between nucleolar and mitotic cycles has beendetermined after treatment of root apices of Zea mays with ethidiumbromide. In the meristematic regions of the stele the two cyclesare not much displaced in relation to each other except fora delay in the onset of the disorganization phase. A few nucleolipersist into metaphase and a few nuclei undergo an amitoticdivision. In the cap initials the drug greatly delays the onsetof disorganization of the nucleolus, which normally occurs beforeprophase in this region. It also delays the completion of reorganizationso that fully organized nucleoli are no longer available duringthe last half of telophase. In the quiescent centre the onsetof disorganization and the end of reorganization of the nucleoliare also delayed in relation to mitosis. There is no evidencefor a delay in the onset of reorganization in any region ofthe meristem. Some cells form multiple micronucleoli and this aberrant behaviouroccurs more often in the cap initials than elsewhere as doesamitotic division.