Crustacyanin, cross-linked with dimethyl pimelimidate to stabilize the protein against denaturation, was used to test the effects of tryptophan modification with BNPS-skatole [3-bromo-3-methyl-2-(nitrophenylmercaptol)-3H-indole] on the ability of the apoprotein to recombine with astaxanthin. The cross-linked apoprotein re-forms alpha-crustacyanin with astaxanthin in reasonable yield following incubation of the protein under the conditions for tryptophan modification in the absence of BNPS-skatole. The BNPS-skatole-treated protein reconstitutes with astaxanthin to give a carotenoprotein with lambda max. at 472 nm, that of the carotenoid in hexane, in a yield similar to that of the BNPS-skatole-untreated control. The implied involvement of tryptophan residues at the sites of astaxanthin attachment in crustacyanin and their possible roles in the binding sites of vitamin A in vitamin A-proteins are discussed in relation to the bathochromic spectral shifts of the chromophores.
