[The effect of medium on functional and structural properties of serum albumins. II. The effect of temperature on the N-form of human serum albumin].

In order to investigate effects of temperature in the physiological range (from 10 to 50 degrees C) on structural, physical and functional properties of the N-form of human serum albumin (HSA), the temperature dependences of fluorescence parameters of Trp-214 residue of HSA and of the specifically bound dye ANS, as well as of association constants of ANS binding in the primary and secondary binding sites on HSA molecule were measured. The temperature-induced changes of these properties of HSA are essentially dependent on pH (7.0 or 5,6) and ionic strength (0.001-0.008 or 0.2 M NaCl). At pH 7.0 and 0.2 M NaCl the environment of Trp-214 remained invariant at temperature changes between 10 and 50 degrees C. On the other hand, the affinity to ANS of a primary binding site doubled and that of secondary ones halved. These affinity changes seem to be due, are least partly, to the heating-induced dissociation of Cl-ions, which are inhibitors of the primary dye binding. By lowering pH (to 5.6) and ionic strength the temperature-induced changes in the Trp-214 environment were observed. The changes are interpreted as indole group transition into the buried region, inaccesible to water (the "closing" of a structural slit). The affinity of secondary binding sites of ANS was halved.