Green Fluorescent Protein is a naturally occurring spontaneously fluorescent protein found in coelenterates, such as the pacific jellyfish Aequorea victoria. Green fluorescent protein is a 27kD native peptide structure containing 238 amino acids. The fluorescence of GFP is a complicated process requiring the involvement of another protein, Aequorin and Ca+2. Aequorin is a complex of 21.4 kDa apoprotein, molecular oxygen and coelenterazine.