The in vivo role of GFP
Several bioluminescent coelenterates such as the jellyfish
Aequorea victoria or the sea pansy Renilla reniformis emit green
light from a green fluorescent protein (GFP).
David Galbraith has
mounted a beautiful picture
of A. victoria.
The GFP's serve as energy-transfer acceptors, receiving energy from a
photoprotein or a luciferase-oxyluciferin
complex in A. victoria and R. reniformis, respectively.
Upon mechanical stimulation A. victoria emits a green light.
However, when the calcium-triggered photoprotein aequorin was puriefied
from A. victoria photocytes, it was found to generate blue,
rather than green light. GFP acts as a secondary fluorescent protein,
receiving energy from activated aequorin. It has been suggested that
radiationless energy transfer is involved, but this subject seems still
under discussion .
The following image summarizes A. victoria bioluminescence
Aequorin (shown on the very left) is a complex of the 21.4 kDa apoprotein,
molecular oxygen and
coelenterazine (an imidazole compound with a molecular weight of 423,
lilac pentagon). When aequorin is activated (second from the left)