Phosphorus-31 NMR reveals for the first time in any species a metabolite that is present in the male but not the female. Male blue crabs produce a metabolite that is absent in females, suggesting a complete enzyme system that is only activated in males. Now that the existence of a sex-specific metabolite has been found for one animal the search is on for others, including ones that might exist in humans.

Hormone levels differ greatly between the males and females of a species, but both sexes do have a full compliment of all the hormones. It is the different concentrations that give rise to the gender gap. The existence of gender-specific metabolites has not been seen before and represents a potentially significant biochemical phenomenon.

"It's possible to speculate that the presence or absence of a sex-specific metabolite might affect an animal's development, anatomy and biochemistry," explains Robert Kleps of the University of Illinois at Chicago, "Differences between the sexes such as disease susceptibility, anatomy or drug metabolism might be due to the presence or absence of a metabolite."

Kleps and colleagues Thomas Henderson and the late Terrell Myers used whole tissue phosphorus-31 NMR to test gill tissue samples from male and female blue crabs, taken from Chesapeake Bay and the gulf coast of Florida over six years. They observed an unusual signal in the gill tissue of male blue crabs that was absent in females, hinting at the presence of a previously unidentified phosphorus compound.

They isolated and analysed this compound and identified it as 2-aminoethyl phosphonate (AEP), an uncommon but well-documented natural metabolite. AEP is not known to be a hormone. It was not at this point possible to rule out differences in diet between males and females as the underlying cause.

Fortunately, while writing the first draft of the paper, Kleps happened to read that a rare gynandromorphic blue crab - one half male, one half female - had been acquired by Romuald Lipcius of the Virginia Institute of Marine Science at the College of William & Mary.

The rare gynandromorph is divided down the middle, with a characteristic blue male claw and a female red claw. The underside of the crab is also visibly divided into male and female halves. After the crab died, Lipcius sent Kleps gill tissue from each side for analysis. "The measured levels of AEP from the male and female gills provided additional evidence that AEP was a sex-specific compound. AEP was seven times more concentrated in the male side as the female side gill," Kleps told SpectroscopyNOW.
He adds that, "AEP is present in normal male gill thus it was expected to be found in the male side gill of the gynandromorph. The fact that the female side had any AEP is explained by the fact that AEP is a natural metabolite that would be distributed throughout the body and incorporated into non-male tissues."

"Since both sides of this strange crab have, of necessity, shared a diet and environment, we had completely independent confirmation of the sex-specific nature of this metabolite," Kleps says. "That blue crabs have this sex-specific compound may be a fluke, or it might represent a common but overlooked process in animal development."
"My hope is that other researchers will expand this work and determine how wide spread is AEP across species and if other less visible metabolites exist in mammals," Kleps told us.

Related links:

• PLoS One, 2007, 2, e780
• Kleps Page
• Lipcius Page
• 2-Aminoethyl phosphonic acid

Article by David Bradley