Comparison of chromosome aberrations, sister chromatid exchanges and unscheduled DNA synthesis in the evaluation of the mutagenicity of environmental factors

Mutagenic character of formaldehyde in vivo was estimated by determining the level of chromosomal aberrations, sister chromatid exchanges and unscheduled DNA synthesis in human lymphocytes. It was found that in case of occupational exposure to formaldehyde the unscheduled DNA synthesis after thiophosphamide treatment in vitro was inhibited and spontaneous level of chromosomal aberrations increased. A negative correlation observed between the unscheduled DNA synthesis and sister chromatid exchanges indirectly confirmed a connection of these exchanges with the DNA repair. The comparison of the results obtained from evaluation of chromosomal aberrations, sister chromatid exchanges and unscheduled DNA synthesis permits suggesting that these methods estimate different sides of the mutagen interaction with a cell and should be considered as mutually complementary methods but not as interchangeable ones.     

Mechanism of nicotinic acid inhibition of the reaction catalyzed by acetyl-CoA carboxylase

A kinetic analysis of the activity of acetyl-CoA carboxylase from chicken liver upon alimentary activation of lipogenesis and inhibition of this reaction by nicotinic acid was performed. It was found that the affinity of the enzyme isolated from chicken liver with stimulated lipogenesis is decreased by nicotinic acid for HCO3- but remains unchanged for ATP. The value of Vmax for ATP and the amount of the ATP used in this reaction remain unaffected. At the same time the enzyme affinity for acetyl-CoA is increased with a simultaneous decrease of Vmax. It is assumed that nicotinic acid inhibits the first step of the acetyl-CoA carboxylase-catalyzed reaction.     

Effect of benzodiazepines on NAD binding to synaptic membrane in the rat brain

The receptor protein solubilized from synaptic membranes specifically binds [14C] NAD (dissociation constant--0.75 microM, capacity of binding sites--0.0125 nmol of metaid per 1 mg of protein). All the studied benzodiazepines (phenazepam, nitrazepam, clonazepam, flunitrazepam) are able to displace [14C] NAD from its receptor sites, the mixed type of inhibition being manifested. An inhibition constant for flunitrazepam, a ligand of benzodiazepine receptors, equals 10 microM. GABA promotes an inhibiting effect of benzodiazepines. It is supposed that neurotropic action of NAD is realized through the GABA-benzodiazepine complex of neuronal membranes.     

c-AMP and Morphogenesis of Acetabularia

The c-AMP content has been found to double when Acetabularia develop from 5–10 mm long to grown or almost full-grown algae.
The biological significance of this fact has been approached by studying the effects of drugs known to influence the intracellular c-AMP content on the development of Acetabularia. When grown in the presence of theophyllin or papaverin, inhibitors of phosphodiesterase, the Acetabularia display a striking response during the exponential growth period; the final length, however, is not affected. Both substances increase the c-AMP content of the algea. Isoproterenol, which activates adenylate cyclase in many systems, also influences Acetabularia during the exponential growth period and, in addition, slightly affects cap formation.
The change in c-AMP content in the course of development and the effects of drugs influencing (theophyllin and papaverin) or likely to influence (isoproterenol) the c-AMP content of the algae suggest that this nucleotide plays a role at the time of intense growth.
The same phosphodiesterase activity has been found in the 5–10 mm and the 19–25 mm long algae, whereas two enzymes were found in cap-bearing Acetabularia.
The results are discussed as well as the involvement of c-AMP in the development of this alga.     

Structure, properties and regulation of acetyl-CoA-carboxylase activity

The paper deals with the analysis of data available in literature and those of the authors' own investigations concerning the structure, properties and regulation of acetyl-CoA-carboxylase. Nicotinic acid is one of the factors regulating the enzyme activity in the animal liver. It inhibits the acetyl-CoA-carboxylase activity through two mechanisms--allosteric regulation and covalent modification. A comparative characteristic of the studied enzyme preparations has shown that administration of nicotinic acid to animals leads to phosphorylation of acetyl-CoA-carboxylase which affects its structure. A complex with homogenic acetyl-CoA-carboxylase is found to contain cAMP-independent and cAMP-dependent protein kinase. The phosphorylation is controlled by citrate competing with nicotinic acid for the coupling sites.     

Action of secondary radiation from 70-Gev protons on the cellular DNA of mammals

A study was made of the effect of secondary radiation of 70 GeV protons on DNA of Chinese hamster cells. With a reference to fibroblast DNA, lymphoid cell DNA, and the lethal effect of radiation on the survival of Chinese hamster cells the RBE was 1.6-7.6, 1.1-3.8 and 1.14-1.7, respectively. DNA breaks were repaired to an equal level after exposure to secondary radiation from the accelerator and gamma-radiation from 60Co in equally effective doses.     

Structural changes in erythrocyte ghosts after irradiation and the initiation of lipid oxidation detectable using 2,6-TNS and fluorescamine

It was shown on erythrocyte ghosts that the parameters of fluorescence of 2,6-toluidine-naphthalene-sulfonate (2,6-TNS) and fluorescamine undergo similar changes after irradiation. After a dose of 100 Gy the equally effective concentrations of Fe2+ were 1-5 microM and 50-100 microM with regard to changes in the rate of fluorescence of fluorescamine and 2,6-TNS, respectively, and greater than 100 microM with regard to fluorescence anisotropy.     

The effect of electromagnetic radiation on the membranes of the sarcoplasmic reticulum

On the sarcoplasmic reticulum membranes has been shown that at temperature of Ca2(+)-ATPase activity change of dependence in the Arrhenius plot the microwaves (2450 MHz, specific absorption rate 12 w/kg) inhibit the ATP-hydrolase and Ca2(+)-transporting activity of Ca2(+)-ATPase. The effect of radiation exhibits within the narrow temperature range (approximately 1 degree C) and quantitatively corresponds to the decrease of Ca2(+)-ATPase activity caused by the decrease of temperature by 1.6 degrees C from 18 degrees C. The fluorescence intensity of naphthalene sulfonic probes reduces under the influence of microwaves at 18 degrees C.