AEQUORIN BIOLUMINESCENCE DISSECTED BY RANDOM MUTAGENESIS

摘要

The photoprotein aequorin is a bioluminescent complex formed from the reaction of the luciferase apoaequorin with its luciferin coelenterazine, which emits light upon Ca2h binding ' Apoaequorin is a 189 aminoacid protein containing three EF-hand Ca2+ binding sites2 whose reaction with coelenterazine results in a stable intermediate containing a coelenterazine peroxide The binding of Ca2+ destabilizes the peroxide and, in the continuous presence of Ca2+, the bioluminescence reaction rapidly goes to completion with a quantum yield of ~ 0.2.' Aequorin luminescence is thus emitted as an exponentially decaying flash, whose peak amplitude increases with [Ca2+].3 The decay rate of this response increases with [Ca2+], while the onset rate and the total light emitted remain roughly constant3 This suggests that the increase of peak amplitude with [Ca2+] is determined by an increase of the decay rate (i.e. rate of luminescence), but not of the reaction yield.