Investigation of the monomeric and oligomeric molecular forms of human growth hormone and poly-L-lysine using fluorescence anisotropy measurement method

This work illustrates the usefulness of fluorescence anisotropy measurement using a long-lifetime fluorescence label bis-(bipyridine)-5-(isothiocyanatophenanthrolin)-Ru(PF6-)(2) for the investigation of large macromolecules - human growth hormone forms with different aggregation degree and poly-L-lysine hydrobromides with different molecular weights. Three molecular forms of this hormone - monomeric and two oligomeric (with polymerization degree 3 and 5) - and poly-L-lysine hydrobromides with different molecular weights were for the first time investigated using fluorescence anisotropy measurement by the constant viscosity. Fluorescence anisotropy and rotational correlation time are determined for each substance. Calculated rotational correlation times in investigated media are linear proportional to polymerization degree of molecular forms of the hormone. Relationship between rotational correlation time and molecular weight of random coil structure poly-L-lysines (with similar molecular weights) is nonlinear. It was shown what measured fluorescence anisotropy of the simple mixtures of two labeled molecular forms of the hormone well corresponds with theoretical anisotropy calculated with average values of the anisotropies of the separately investigated pure compounds.