Mavicyanin, a Blue Copper Protein from Cucurbita pepo medullosa

1 The copper protein mavicyanin has been isolated and purified from the green squash Cucurbita pepo medullosa. 2 Mavicyanin contains one type-1 copper/18000 Mr, which can be characterized by: intense absorption maximum at 600 nm (ɛ= 5000 M−1 cm−1/Cu, A280/A600= 8.0 ± 0.5, A600/A403= 7.0 ± 0.25, maximum of fluorescence emission at 335 nm. 3 In the oxidized state the copper of mavicyanin is 100% detectable by electron paramagnetic resonance (EPR). Computer simulation of the rhombic EPR signal gives gz= 2.287, gy= 2.077, gx= 2.025, Az= 3.5 mT, Ay= 2.9 mT and Ax= 5.7 mT. 4 Like other simple type-1 copper proteins, such as stellacyanin, azurin or plastocyanin, mavicy-anin is readily reduced by hydroquinone or L-ascorbic acid. Its midpoint potential E′m was determined to be + 285 mV. The reduced protein reacts rather slowly with dioxygen, but is rapidly reoxidized by ferricyanide.