Lobster colour-change mystery solved

[Althalus]

A group of UK researchers has solved the long-standing puzzle of why cooking changes lobsters from blue to orange. And they think the findings could have important implications for drug delivery.

Raw lobsters get their distinctive blue-purplish colour from a pigment called astaxanthin. The pigment molecules are pinkish-orange in their free, unbound form, but when they bind to a protein in the lobster's shell, their shape and light-absorbing properties are distorted. As a result, they appear blue.

A team led by John Helliwell at the Daresbury Laboratory in Warrington, has now found that the shell protein, called Beta-Crustacyanin, becomes irreversibly denatured and so changes shape when cooked. This allows the pigment molecules to resume their free-form, and so appear orange.

The team first had to solve the chemical structure of parts of these pigment-bound proteins using X-ray crystallography.

"People have been trying to crystallise these proteins with astaxanthin bound to them for 15 years, and failed," says researcher Naomi Chayen, at Imperial College.

Very slow

The reason, it turns out, is that the insoluble crystals grow very slowly and are very sensitive to X-rays used during analysis.

Chayen used a home-grown technique for growing the crystals, called Microbatcing. This involved covering them with oil to reduce any evaporation.

After two months there appeared to be no growth. "I very nearly gave up," she says. However, her perseverance paid off and after four months she had the crystals she needed. They were then analysed using the "soft" X-rays of the Synchrotron Radiation Source, at the Daresbury Laboratory.

The findings could yield techniques for delivering water-insoluble drugs, says researcher Peter Zagalsky at Royal Holloway, University of London.

Zagalsky plans to study the structure of B-Crystayanin, to discover how it binds to the water-insoluble astaxanthin. This could lead to new compounds capable of carrying drugs that do not dissolve in water, and capable of targeting specific tissues, he says.

Journal reference: Proceedings of the National Academy of Sciences (vol 99, p9795)