The lobster carapace carotenoprotein, α-crustacyanin. A possible role for tryptophan in the bathochromic spectral shift of protein-bound astaxanthin

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.

Influence of Tryptophan Modification upon Digestion of Antithrombin III by Elastase

SummaryChemical modification of tryptophan residues in antithrombin III by dimethyl (2-hydroxy-5-nitrobenzyl) sulfonium bromide (HNBSB) generates products with similar levels of modification (equivalent to 0.9 mole 2-hydroxy-5-nitrobenzyl [HNB] incorporated/mole of antithrombin III) but with high or low affinity for heparin-Sepharose. Upon digestion with pancreatic or neutrophil elastase the low affinity forms generate a product of molecular weight form (55 kDa) not seen in digests of native antithrombin III or modified forms with high affinity for heparin. When measured as loss of activity the obserued rate of digestion of the latter in the absence of heparin was more rapid than that of native antithrombin III. The differences in digestion are considered to be related to conformation at differences between the various forms.