ABSTRACT
The transcriptional activities of the nuclei of the liver and spleen cells of rats were studied at the 1st, 4th, 18th, and 24th hour after whole-body irradiation with gamma rays. It was found that the transcriptional activity of the nuclei of rat spleen was invariably markedly suppresed in all the periods after irradiation while that of the rat liver demonstrated a diphasic change, that is, an exaggeration of the activity at the 4 th hour but a reduction at the 18th and 24th hour after irradiaiton. The change of the activity of RNA polymerase Ⅱ showed no difference from that of RNA polymerases Ⅰ+Ⅲ. The mechanism of these changes was briefely discussed.
ABSTRACT
α-Amylases from control and gamma-irradiated (at 0.2 and 2.0 kGy dose levels) wheat seedlings were purified to homogeneity and characterized. The molecular weight of the enzyme from a 2 kGy irradiated sample was slightly lower than that of the control; other general and catalytic properties also showed some differences. α-Amylase from the irradiated (2 kGy) sample had a narrow range of pH optimum and was inactivated faster at alkaline pH and by heat treatment than the enzyme from unirradiated wheat. A high apparent Michaelis constant (Km) and a low maximal velocity (Vmax) for the hydrolysis of soluble starch catalyzed by the enzyme from irradiated (2 kGy) wheat, suggested some modifications in the formation of the substrate α-amylase complex. Further, of the total number of amino acid residues lost on irradiation, dicarboxylic amino acids constituted the largest percentage; these structural alterations in the enzyme may be responsible for its partial inactivation. The total sugars liberated upon amylolysis of starch with the 2 kGy irradiated enzyme were lower than control, and there was accumulation of higher maltodextrins in the place of maltose.