An alterative exciton model has been firstly described

where three identical β chromophores at inner of the allophycocyanin(αβ)

3

disk with

C

3

-symmetry and brought close togather and coupled by strong exciton mechanism.Meanwhile

accurate absorption and circular dichroism(CD)spectra of allophycocyanin(αβ)

3

、(αβ)

as well as a andβ subunits are obtained

and analyzed by deconvolution methods.The deconvolutionresults of these observed spectra togather with ths theoretical analysis of the exciton model have taken an estimate of the relative chromophore orientations of the transition dipole moments.The exciton splitting energy and the distance of adjacent βchromophores in allophycocyanin(αβ)

3

have also been deduced in this paper.