[Modification of the DNA spatial structure when complexed with cisplatin]. / Modifikatsiia prostranstvennoi struktury DNK v komplekse s tsis-platinoi.

The experimental and theoretical analyses of the conformational transitions of DNA-cis-platinum complexes have been carried out. It is shown that at low concentrations of the ligand, the thermodynamic parameters of the helix-coil transition of the complexes are not the result of the local B-->A transition.

[Selective effect of ionization of nitrogen bases on the thermostability of AT- and GC-pairs of DNA]. / Izbiratel'noe vliianie ionizatsii azotistykh osnovanii na termostabil'nost' AT- i GTs-par DNK.

The ionization specific influence of nitrogen bases on thermostability of AT- and GC-pairs of DNA has been investigated by the method of DNAs melting temperature analysis. It has been shown that the change of temperature interval of DNA helix-coil transition when changing pH environment is due to specific ionization of AT- and GC-pairs of nitrogen bases.

[Intensity of the Feulgen reaction depending on the method and duration of fixation]. / Ob intensivnosti reaktsii Fël'gena v zavisimosti ot sposoba i prodolzhitel'nosti fiksatsii.

A comparative cytophotometric investigation of DNA-fuchsine content in mature erythrocytes of chicks was carried out using various methods and duration of fixation: 96 degrees and 100% ethanol, Carnoy's fixative, and mixtures of 40% formalin--96% ethanol--glacial acetic acid /GAA/(9 : 3 : 1), 100% methanol--4% formalin--GAA (17 : 2 : 1), and 96% ethanol--GAA (3 : 1)+formalin (final concentration 2%). The duration of fixation varied from 15 to 150 minutes, with 15 minutes intervals. It has been shown that the quantity of DNA--fuchsine (under equal conditions of the Feulgen reaction) depends greatly on the method and duration of fixation. Of the fixatives investigated the best is the mixture of 96% ethanol--GAA (3 : 1)+formalin 2%, after which the Feulgen reaction runs more intensively, and practically does not depend on the fixation duration. The structure of chromatin (determined by the distribution character of optical densities in each point scanned) is also best preserved. The Carnoy fixative occupies, by these parameters, the last place. The mechanisms of interaction of the above fixative with the nuclear DNP are discussed briefly.

[Effect of the hydrolyzing solution temperature, acid concentration and the duration of the hydrolysis on the intensity of the Feulgen reaction]. / Vliianie temperatury gidrolizuiushchego rastvora, kontsentratsii kisloty i prodolzhitel'nosti gidroliza na intensivnost' reaktsii Fël'gena.

The quantity of DNA-fuchsin in the cock monocytes and erythrocytes has been measured by scanning cytophotometric methods and computer analysis. Hydrolysis was carried out using 1 N HCl (60 degrees C, 4-30 min) and 5 N HCl (37 degrees C, 4-36 min, and 22 degrees C, 10-150 min). The elevation of the temperature from 22 degrees to 37 degrees resulted in a 5-fold reducing of the time required for achieving the maximum of the hydrolysis curve, although the DNA content at the maximum point decreased by 7-9%. At 60 degrees and 1 N HCl, the loss of DNA reaches up to 30%. The prolongation of the hydrolysis time caused even more losses of DNA: at 60 degrees they are equal to 70% (22 minutes following the maximum point), at 37 degrees it is equal to 55% (26 minutes) and at 22 degrees only 9.5% (100 minutes) (the quantity of DNA at the maximum point is taken for 100%). During all the experimental conditions and in both the cell types, the hydrolysis curves are monomeacked, and at 22 degrees starting from 30 minutes a plateau is observed with a slight increase towards the 50th minute. The quantity of DNA-fuchsin in the loose nuclei of monocytes is generally higher than in compact nuclei of erythrocytes. The analysis of scanning- and histograms has shown that the "storage" of DNA in the erythrocyte nuclei and its loss during hydrolysis are related to the fact that apurinization of DNA in the compact chromatin is getting more slowly, whereas its loss due to depolymerization-extraction is higher than in the loose chromatin. These phenomena are expressed least of all during "cool" hydrolysis. The above circumstances should be taken into account during the analysis of nuclei with different degrees of DNA density. Hydrolysis in 5 N HCl at 22 degrees is recommended.