Spectroscopic study of trypsin, heat and Triton X-100-induced denaturation of the chlorophyll-binding protein CP43

Trypsin-, heat- and Triton X-100-induced denaturation of CP43, the core antenna complex of photosystem II purified from spinach, has been investigated using absorption, fluorescence and circular dichroism spectroscopy. Triton X-100 was found to bring about considerable dissolution of pigments from the protein to the monomeric state in solution and destruction of the interactions among the chlorophyll, carotene and protein. Heat induced significant unfolding of the protein secondary structure and loss of excitonic interactions of the pigments, but no apparent dissolution of the pigments from CP43. Trypsin caused structural changes in the extrinsic part of the protein but no change of the native state of the pigments. Trypsin, heat and Triton X-100 treatments increased the light sensitivity of chlorophyll in CP43 to different extents. The results suggest that the protein and β-carotene can protect the chlorophyll from light-induced destruction in CP43.