The changes in the structure and RNA-polymerase activity of rat liver cell chromatin after a single injection of cycloheximide (3 mg/kg of body mass) were studied. The cycloheximide-induced fluctuations in protein synthesis rates are concomitant with episodes of drastic changes in the chromatin structure. The reorganization of the general protein structure is associated with an increase or a decrease of the RNA-polymerase II activity. The data obtained suggest that the activation-inactivation of RNA-polymerase II in cell nuclei is due to reorganization of chromatin infrastructures--from higher levels of the electron-dense chromatin package to the unfolded nucleosomes of the transcriptionally active protein.
Using the 31P-NMR method, the composition of the pool of phosphate-containing metabolites in intact rat liver 72 hours following the blocking of protein biosynthesis by cycloheximide was studied. It was shown that during maximal inhibition, i.e., 2-3 hours after cycloheximide injection, the ATP concentration decreases approximately 5-fold, that of ADP and sugar phosphates--4- and 2-fold, respectively. The intracellular pH in hepatocytes was followed by measuring the chemical shift of the Pi signal. The reconstitution of intracellular pH after 2-3 hours is consistent with changes in the Pi level in hepatocytes. The experimental results were compared with the data of biochemical analysis. NMR seems to be a promising tool in the study of metabolism of various animal organs and tissues under physiological and pathological conditions.
The responses of deoxyribonucleotide (dNTP), DNA, and protein synthesis systems in blood-forming organs of animals (dogs, mice) as well as changes in Fe(3+)-transferrin (Fe(3+)-TF) and Cu(2+)-ceruloplasmin (Cu(2+)-CP) pools in blood to gamma-irradiation and the administration of radioprotectors have been studied. It has been shown that changes in Fe(3+)-TF and Cu(2+)-CP pools in blood are indices of changes of body radioresistance and are reliably controlled by the EPR technique. An increase in the Fe(3+)-TF pool promotes the activation of synthesis of dNTP, DNA, and Fe(3+)-containing proteins, which are essential for repair efficiency during early post-irradiation time as well as for the development of compensatory and restorative reactions of cellular systems; i.e., they are responsible for body resistance to DNA-damaging factors. It is important that the intensity of responses depends on the initial state of the organism. Thus, dogs with initial individual characteristics of blood typical for suppressed or activated states had abnormally high responses to irradiation by low doses of 0.25 and 0.5 Gy. This fact is important for the estimation of consequences of prolonged low-dose irradiation for human population. It has been shown that radioprotectors, efficient in survival test activate the synthesis of dNTP, DNA, and proteins in organs. The intensity of dNTP synthesis and the time when dNTP pools get maximum values determine the efficiency of protectors and the time of irradiation after their administration.
Polyribosomes isolated from the rat liver in a medium with low ionic strength were irradiated by "hot" tritium atoms under conditions providing for the replacement of the hydrogen atoms located at the surface of polyribosomes by tritium. After fractionation of such polyribosomes, the radioactivity of the obtained fractions was measured and their proportions were calculated for the total surface accessible for the tritium atoms (in %), as well as their specific radioactivity. The material loosely associated with the polyribosomes and containing amino acyl-tRNA-synthetases is more radioactive than rRNA and r-proteins, especially concerning their specific radioactivity. This suggests that the material is organized as individual molecules located on the surface of ribosomes. The specific radioactivity of the RNA-component of this material (tRNA) is twice that of proteins, thus suggesting its surface localization in the composition of loosely associated material. Based on the pattern of labeling of rRNA and r-proteins of the native and preliminarily dissociated polyribosomes, we propose that the material, loosely associated with the polyribosomes, has affinity to both rRNA and r-proteins.
