We treat theoretically conformational transitions in DNA-ligand complexes allowing for the existence of different binding parameters of the ligand to different DNA conformations. The parameters of binding are determined from the best fit of the theory to experimental data for the difference between transition point (Tm) and the width of transition curve (delta T) for the complexes and for naked DNA. The analysis shows that Ethidium Bromide (EB) and Actinomycin D (AMD) each may form at least five types of complexes: three types (one "strong" and two "weak") with helix DNA and two types ("strong" and "weak") with single-stranded DNA. The parameters of the complexes have been obtained. Some testable experimental predictions of the theory are also discussed.

The enthalpy of helix-coil transition of DNA (delta H) is determined from the experiments on DNA melting with ligands by means of absolutely general formula, which contains only values directly known from the experiment (M.D. Frank-Kamenetskii, and A.T. Karapetian, Mol. Biol. USSR 6, 621 (1972)) with the combination of the "area" method (P.O. Vardevanian, et al., Biophysica 28, 130 (1983)). The experimentally obtained data show that delta H depends on both concentration of Na+ in solution and GC-content of DNA and is of high accuracy.

The effect of ligand interacting with native DNA by two types on the parameters of helix-coil transition in homopolymers is considered using the most probable distribution method (Yu.S. Lazurkin et al., Biopolymers 1970). It is shown that at a small relative concentration of ligand the melting enthalpy (delta H) of DNA may be obtained from the universal formula which contains only values directly known from the experiments. It is shown that the formula for the change of melting temperature and width of melting range depending on the total ligand concentration in solution is converted into the corresponding formulae which are defined for the case when only one type of interaction of ligand and DNA is considered.

Исследовано влияние электромагнитных волн миллиметрового диапазона (ММ ЭМВ) на взаимодействие метилового или кристаллического фиолетового с сывороточным альбумином человека (САЧ) с помощью методов УФ- денатурации, флуоресцентной и КД (круговой дихроизм) спектроскопии. Показано, что воздействие ММ ЭМВ приводит к ослаблению стабильности САЧ и понижению силы взаимодействия между САЧ и метиловым фиолетовым (МФ). Выявлено также, что влияние ММ ЭМВ нерезонансными для воды частотами, которые воздействуют прямо на структуру САЧ изменяет его вторичную структуру, в то время как облучение резонансной для воды частотой не вызывает структурных изменений, однако ослабляет стабильность в большей степени. The effect of millimeter range electromagnetic waves (MM EMW) on methyl or crystal violet interaction with human serum albumin (HSA) has been studied, using the UVdenaturation, fluorescence spectroscopy and CD spectroscopy methods. It was revealed that MM EMW irradiation leads to weakening of the stability of HSA and decreasing of interaction force between HSA and methyl violet (MV). It was also shown that MM EMW irradiation by water non-resonant frequency, affecting immediately the structure of HSA, changes its secondary structure, while the irradiation by water-resonant frequency does not invoke structural changes, but weakens the stability in higher degree.

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