September 30, 1999--The nematode worm Ascaris lumbricoides, an intestinal parasite that infects one billion people worldwide, has uncommonly strong hemoglobin that binds to oxygen 25,000-times more tightly than does human hemoglobin. The affinity of Ascaris hemoglobin for oxygen is so powerful that many researchers believed the molecule could not possibly play a role in respiration.
Learning the true function of Ascaris hemoglobin and understanding how and why the worm's hemoglobin embraces oxygen molecules so tightly have been great challenges, said Howard Hughes Medical Institute (HHMI) investigator Jonathan Stamler. "Why would a molecule that functions as an oxygen carrier bind oxygen so tightly that the oxygen molecules would never come off?"
Two collaborating groups of HHMI scientists have ferreted out the secrets of this oxygen-hungry molecule by using a variety of biochemical techniques and by taking physical measurements of the hemoglobin inside the worm. In so doing, they have identified a biochemical link between the hemoglobins used by primordial bacteria to detoxify themselves of atmospheric gases and the modern mammalian hemoglobins that underpin respiration.
The findings not only open a window to understanding how a wide variety of organisms evolved to utilize or guard against atmospheric gases such as oxygen and nitric oxide, but they may also provide new ideas for ways to starve cancerous tumors of oxygen.
In the September 30, 1999, issue of the journal Nature, research groups led by Stamler, an HHMI investigator at Duke University, and Daniel Goldberg, an HHMI investigator at Washington University in St. Louis, describe how Ascaris hemoglobin acts as an enzyme to neutralize oxygen, which in high doses is toxic to the worm.