Cockroach chemist

The fast and most ancient land insect on earth, the American cockroach, Periplaneta americana, turns out to be also a spectacular organic chemist, according to S.A. Shukolyukov and V.S. Saakov, researchers from the Sechenov Institute of Evolutionary Physiology and Biochemistry in St Petersburg. They have discovered that P. americana can synthesize a chemical no other animal is known to be capable of, the carrot-lovers' best friend: beta-carotene.

The carotenoid compounds, including beta-carotene, are essential components of our diets, acting as precursors to the chromophoric molecule rhodopsin, the pigment of vision. Without carotenoids in the diet, animals, including ourselves, would suffer serious vision defects and potentially blindness.

The Sechenov researchers have demonstrated that mosquitoes and butterflies fed a carotenoid-deficient diet become almost completely blind very quickly. But, American cockroaches are not struck with the affliction.

To prove that the insects are synthesizing beta-carotene rather than letting their sight go, the researchers injected the insects with radioactively labelled pyrophosphate of mevalonic acid (a beta-carotene precursor). Within 24 hours labelled beta-carotene could be extracted from the insects, showing that they had indeed carried out a conversion of the precursor to final product, overnight. The researchers are amazed by the finding and, having carried out the experiment over three years, they have established that over four cockroach generations, despite a total lack of carotene in the insects' food, they could always make enough for their visionary needs.

The team has not yet figured out the biochemistry underlying the beta-carotene synthesis, but they suspect that the insects carry microbes in their gut with the appropriate specialist enzymes for the conversion. Regardless, the world's oldest insect, unlike any other animal, sees the sense in a "belt and braces" approach to ensuring adequate levels of its visual pigments through diet and synthesis.

Biochemistry (Moscow), 2001, 66(5), 535