Animal carotenoids—28. Further studies on the carotenoprotein alloporin ex. Allopora californica

Abstract

1. 1. The carotenoprotein alloporin ex Allopora californica contains optically pure (3S,3′S)- astaxanthin as prosthetic group, here confirmed by the camphanate method. 2. 2. Individual recombinations are reported for the colourless apoalloporin with the three isomers of astaxanthin (3S,3′S; 3R,3′S, meso and 3R,3′R), (3S)- adonirubin and (3R,3′R)-actinioerythrol to semisynthetic carotenoporteins. The carotenoprotein with (3S,3′S)- astaxanthin as prosthetic group exhibited the largest bathochromic shift. 3. 3. The Cotton effects of apoalloporin and of the semisynthetic carotenoproteins based on the three astaxanthin isomers, were very similar. 4. 4. Gel filtration data together with previous mol. wt determination suggest that alloporin is not a globular protein, consistent with a high content of helix-breaking amino acids. 5. 5. Apoalloporin appeared from 1H NMR, 13C NMR and CD data to have a quaternary structure similar to that of alloporin. However, gel filtration data revealed a lower equivalent Stokes radius. 6. 6. The quantitative amino acid composition of alloporin is reported. An exceptionally high content of acidic amino acids may explain the stable arrangement of alloporin in the CaCO 3 skeleton of the coral.