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Tyr-72 is included in the hydrophobic cleft which is formed in the histone H1 globular head. Tyr-72 is screened against polar aqueous environment and its intramolecular mobility is sharply retarded. This microenvironment causes a red shift (lambda max = 279 nm) and a sharpening of the longer wavelength shoulder of absorption spectra, a high fluoresence anisotropy value (A = 0,11), high quantum yield of fluoresence (approximately 0.2) and a decrease of the Stern-Volmer Constant during quenching of histone H1 fluorescence by acrylamide. It has been found that the change in the intensity of histone fluorescence at lambda excit = 265 nm, but not at lambda excit = 280 nm, is due to the changes in the quantum yield of fluorescence. The increase of fluorescence intensity at lambda excit = 280 nm depends on the changes in the quantum yield and molar extinction coefficient of histone H1 tyrosyl chromophore. The change in the ratio of fluorescence intensity exited at 280 nm (F280) to the fluorescence intensity excited at 265 nm (F265) corresponds to the change of delta epsilon 286 in difference absorption spectra. The introduction of the parameter Cf = F280/F265 allows one to go over to studying excitation spectrum shifts instead of histone absorption spectrum shifts, which is much more convenient methodologically since in this case it is possible to carry out research using lower protein concentrations and turbid solutions. The results make it possible to designate Tyr-72 of histone H1 as a special class of fluorescent tyrosyls whose properties differ from those of tyrosyls of other tryptophane-free proteins: RNAase, insulin, core histones--H2A, H2B, H3, H4 and some others.

The spatial organization of the histone dimer (H2A-H2B) in 0.1-1.0 M NaCl is characterized by the inclusion of 38% of the residues in alpha-helical segments, an average fluorescence quantum yield of 0.085 +/- 0.003, a red shift of absorption (lambda max = 278 +/- 0.5 nm) and fluorescent spectra (lambda max = 304.4 +/- 0.3 nm) as compared to the respective spectra of free tyrosine. The changing of position lambda max of tyrosine fluorescence of histones during denaturation has been shown. The dimer (H2A-H2B) exhibited a conformational change in a transition centred at about 0.5 M NaCl. The dimer denaturation takes place at higher urea concentrations as the ionic strength of the medium increases. The quenching of tyrosine fluorescence of the histone dimer (H2A-H2B) was performed using the ions I-, Cs+ and acrylamide. It has been shown that, at a concentration of NaCl over 0.5 M, dimer compactization takes place, as well as the screening of some part of tyrosyls for te against the quenching effect of Cs+. Our experiments made it possible to identify three zones in the composition of the histone dimer (H2A-H2B) and determine the number (ni) and fluorescence quantum yields (qi) of tyrosyls included in the following specific zones: zone I, n1 = 2, q1 = 0.136; zone II, n2 = 3; q2 = 0.08; zone III, n3 = 3; q3 = 0.055.