Purification and characterization of a blue-colored red-fluorescent protein from the silkworm (Bombyx mori L.) larvae

1. 1. A red-fluorescent blue protein (P600) was purified from the digestive juice of the silkworm (Bombyx mori L.) larvae raised on mulberry leaves. 2. 2. The purified protein was electrophoretically homogeneous and showed the absorption maxima at 601.5 nm and 278 nm, and the fluorescence maximum at 621 nm. 3. 3. The molecular weight was estimated to be 540,000 by gel filtration on Sepharose CL-6B. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate suggests that the protein consists of two heterogeneous polypeptide subunits with a mol. wt of 15,000 and 18,000. 4. 4. The P600 contains excess acidic amino acid residues over basic groups. The polarity and pI were 45.5% and 4.6, respectively. 5. 5. The production of H₂O₂ was observed in the presence of P600 upon illumination.