Fluorometric detection of low temperature thermal transitions in the Clq component of human complement

Fluorescence studies with the human complement component Clq were performed as a function of temperature and demonstrated the existence of low temperature, thermally induced structural transitions in the Clq molecule. Both intrinsic protein fluorescence and the fluorescence of the apolar probe 2-p-toluidinylnaphthalene-6-sulfonate independently showed thermal transitions at 15°C, 35°C and 48°C. Clq activity measurements indicated no loss of hemolytic activity at temperatures below 46°C. It is proposed that these structural transitions are a consequence of the internal flexibility of the native Clq molecule.