The blush of a lobster¿s shell during cooking is extraordinary by any measure. Exactly why the shift from purplish-blue to fiery crimson occurs has long eluded explanation. But new research is at last revealing the molecular mechanism underlying the phenomenon.

The key, say Michele Cianci of the University of Manchester and colleagues in a report published recently in the Proceedings of the National Academy of Sciences, is the lobster shell protein beta-crustacyanin. In living lobsters, this molecule binds a pigment molecule known as astaxanthin, flattening it and thus rendering it blue (a good color for crustacean camouflage). In its unbound form, however, astaxanthin is reddish-orange in hue. Cooking the lobster, it turns out, denatures the beta-crustacyanin such that it frees astaxanthin, thereby setting the shell ablaze.

Probing the color change required that the team use x-ray crystallography to analyze the beta-crustacyanin complex¿s three-dimensional structure. This was no easy task: as its name suggests, the technique requires crystals of the pigment-bound proteins--crystals that classic growing methods failed to produce. Team member Naomi Chayen of Imperial College London eventually cultivated the crystals using the so-called Microbatch method, in which they are grown in oil.

Chayen notes that in addition to resolving a longstanding biological puzzle, the new findings might have intriguing biomedical applications. "This could lead to an important new use of astaxanthin as a drug-delivery mechanism for medicines that are insoluble in water, and give designers of new food colorants or dyestuffs an interesting new capability," she remarks.