[Effect of low-intensity 900 MHz frequency electromagnetic radiation on rat liver and blood serum enzyme activities].

The comparative analysis of the rat liver and blood serum creatine kinase, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and purine nucleoside phosphorylase post-radiation activity levels after a total two-hour long single and fractional exposure of the animals to low-intensity 900 MHz frequency electromagnetic field showed that the most sensitive enzymes to the both schedules of radiation are the liver creatine kinase, as well as the blood serum creatine kinase and alkaline phosphatase. According to the comparative analysis of the dynamics of changes in the activity level of the liver and blood serum creatine kinase, alanine aminotransferase, aspartate aminotransferase and purine nucleoside phosphorylase, both single and fractional radiation schedules do not affect the permeability of a hepatocyte cell membrane, but rather cause changes in their energetic metabolism. The correlation analysis of the post-radiation activity level changes of the investigated enzymes did not reveal a clear relationship between them. The dynamics of post-radiation changes in the activity of investigated enzyme levels following a single and short-term fractional schedules of radiation did not differ essentially.

[Influence of ionizing radiation on enzymatic activity and state of nucleus-nucleolar apparatus in rat hepatocytes].

The effects of a single exposure of rats to the whole-body roentgen irradiation at the doses of 3.5 Gy and 4.5 Gy on the activity of creatine kinase, purine nucleoside phosphorylase, alanine aminotransferase, aspartate aminotransferase, as well as on the state of the nuclear-nucleolar apparatus in rat hepatocytes on the 6th and 13th days after radiation exposure have been studied. Irradiation at the above doses induced changes in the levels of enzymatic activity of different values and different directions within the same time periods, as well as oscillating changes in this type of enzymatic activity over time. This demonstrates various radiosensitivity and adaptation abilities of these enzymatic activities. The changes in the enzymatic activity significantly correspond to the changes in the morphometric indices of nuclear-nucleolar apparatus of hepatocytes, as well as the distribution of hepatocytes within the ploidy classes: in particular, stabilization of the enzymatic activity on the 13th day after irradiation correlates with the increased transcriptional activity, which is detectable through the increased number of nucleoli per nucleus and the expanded space of a hepatocyte nucleus. The compensation mechanisms are likely to be targeted at the changes in the functional activity of surviving hepatocytes, rather than at the replacement of the damaged cells by the new ones.

[Purine nucleoside phosphorylase inhibitors and their clinical significance].

PNP catalyzes a reversible phosphorolysis of purine deoxy- and ribonucleosides with formation of (d)Rib-1-P and appropriate bases. PNP plays a leading role in the cell metabolism of nucleosides and nucleotides, as well as in maintaining the immune status of an organism. The major purpose of the majority of studies on the PNP is the detection of high-performance enzyme inhibitors, derivatives of the purine nucleosides, which are used in medicine as immunosuppressors. It is well known that the latter are necessary for creating a selective T-cell immunodeficiency in a human body under organs and tissue transplantation. The review discusses the issues related to deliberate synthesis of effective, metabolically inert, and low-toxic PNP inhibitors. It also analyzes the available studies on substrate and inhibitory properties of the analogues of purine nucleosides, as well as research on the structural factors which reinforce the inhibitor activity of those analogues. The inhibitors which are either used in medical practice or are currently at a stage of preclinical testing are described. The inhibitors which are more efficient in their influence on the PNF from tumorous tissues are of special interest. Using PNP inhibitors in case of a number of pathologies denotes the importance and promise of research on both the enzyme and the compounds affecting its activity.

[Purification and various properties of creatine kinase MM isoenzyme from the human heart muscle]. / Ochistka i nekotorye svoistva izofermenta MM kreatinkinazy iz serdechnoi myshtsy cheloveka.

Homogeneous preparation of creatine kinase MM isoenzyme was isolated from human heart muscle using affinity chromatography on Sepharose containing immobilized Cibachron blue F3G-A. The enzyme was active at a wide range of pH 5.0-8.0 exhibiting maximal activity at pH 6.0-6.7. Dependence of the initial rate of creatine kinase reaction on the ADP concentration at pH 6.6 in presence or absence of Mg2+ did not follow the Michaelis-Menten kinetics, while hyperbolic dependence was found at pH 7.6 and pH 5.2. In presence of Mg2+ Km value for ADP at pH 7.6 and pH 5.2 was decreased 4-fold and 1.3-fold, respectively, whereas Vmax was increased 2-fold and 2.5-fold, respectively. Besides, Km value for Mg2+-ADP at pH 7.6 was 3-fold higher than at pH 5.2, while these Km values were similar for ADP. The data obtained suggest that in human heart functional dissimilarity of creatine kinase MM subunits appears to occur, which is of importance in regulation of transphosphorylation.

[Escherichia coli K-12 mutants assimilating adenine via a new metabolic pathway]. / Mutanty Escherichia coli K-12, usvaivaiushchie adenin po novomu metabolicheskomu puti.

Two pathways of adenine utilization are only known in Escherichia coli K-12: the conversion to adenosine monophosphate by adenine phosphoribosyltransferase (apt gene) and ribosylation to adenine nucleosides by purine nucleoside phosphorylase (deoD gene). The purine auxotrophs defective in synthesis of inosine monophosphate de novo (pur) and carrying apt and deoD mutations cannot satisfy their purine requirements by exogenously supplied adenine or adenosine. We have selected spontaneously secondary-site revertants (designated adu) of pur apt deoD mutants, by plating on adenine or adenosine as the sole purine source. The adu mutations frequency was 6-10(-7). The phenotypical suppression of adenine phosphoribosyltransferase and purine nucleoside phosphorylase deficiency by adu mutations is neither the consequence of apt + or deoD + reversions nor the result of appearance in mutant cells of any activity converting adenine to adenosine monophosphate or adenosine. Adenine utilization in adu mutants is not caused by constitutive synthesis or genetic modification of the substrate specificity of adenosine deaminase (add gene). The direct deamination of adenine to give hypoxanthine in extracts of adu2 mutant has been shown. The data obtained suggest the possibility of a new adenine deaminase activity to appear in E. coli by means of single mutations.