P-Crustacyanin

In p-crustacyanin, several amino acids of the apoproteins form hydrogen bonds to two molecules of astaxanthin (Fig. 7.25). [39, 43] The two astaxan-thin molecules are at a distance of 7 A and constitute an exciton coupling system. Further, and perhaps more significant contributions to the enormous bathochromic shift are due to the elongation of the n-system, caused by the coplanarity of the cyclic end groups and by partial polarisation of the keto-groups. 

P. F. Zagalsky, E. E. Eliopoulos, and J. B. Findlay, The lobster carapace carotenoprotein, alpha-crustacyanin. A possible role for tryptophan in the bathchromic spectral shift of protein-bound astaxanthin, J. Biochem. 274 (1991) 79-83. 

Figure 8-3. (a) ASX in hexane at a dilution similar to that in lobster crustacyanin (left) (b) beta-crustacyanin (right). From Dr P Zagalsky with permission (see color plate section)... 

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