A novel red fluorescent protein from the deep sea luminous fish Malacosteus niger

Abstract

1. 1. A protein, blue in daylight and red fluorescent under ultraviolet (366 nm) light, has been extracted and partially purified from the red-emitting suborbital luminous organ of the deep sea fish Malacosteus niger. 2. 2. The protein had a molecular weight on G-100 Sephadex of approx. 32,000 and on SDS polyacrylamide gel electrophoresis of approx. 30,000. 3. 3. The absorbance maxima of the isolated protein were at 555 nm and 612 nm. 4. 4. There were four fluorescence excitation maxima (305, 332, 374 and 392 nm) corresponding to two emission maxima (564 and 626 nm; 564 nm for 305 nm and 374 nm and 626 nm for 332 nm and 392 nm). 5. 5. The protein exhibited a low intensity phosphorescence after exposure to visible light. 6. 6. The chromophore appeared to be covalently bound, some being extracted in acid methanol at 0°C or in boiling methanol. 7. 7. The protein has characteristics similar to a phycobiliprotein, previously found only in blue-green and red algae. 8. 8. Similar, but not identical, proteins were also isolated from two other related stomiatoid fishes, Aristostomias and Pachystomias.