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Early-Earth Oxygen Carriers Found

By Pippa Wysong, Access Excellence


Honolulu, HA (07/15/04)- A primitive form of hemoglobin has been found in single-cell microbes living in extreme environments, and is providing an important clue about the way hemoglobin developed and changed over the past 2.5 billion years.

A. Pernix protoglobinHemoglobin is a molecule in blood that binds and transports oxygen in living creatures, but whether it existed in early life forms on the planet was not known, until now. The primitive hemoglobin structure, also called a protoglobin, is believed to have been used in the ancient world to detect and bind oxygen, possibly using the oxygen in the production of energy.

"It was very surprising to us that bacteria-like organisms which date back 3.5 billion years would have a human-like hemo-globin protein," said Maqsudul Alam, PhD, a microbiologist at the University of Hawaii, Honolulu.

Researchers began their path to the discovery of the protoglobin after they came across an important clue. In the modern day Aeropyrum pernix, of the archaea kingdom, they discovered the presence of a specific protein known to be associated with hemoglobin. A. pernix is an extremophile that lives in near-boiling water with high salt concentrations. Researchers then studied another archaea organism, M. acetivorans, which is found in mud and identitied the same protein there.

The protein that they found had almost exactly the same structure as human myoglobin, a molecule that stores oxygen in muscle tissue and has a structure similar to hemoglobin. Humans have both hemoglobin and myoglobin.

"The question was, what was the origin of these proteins," said Dr. Alam. Archaea are primitive organisms that tend to live in extreme environments, these areas being similar to conditions on early earth. Going back billions of years, "there was no oxygen, the atmosphere consisted mostly of gases such as nitric oxide, carbon monoxide and hydrogren sulfide," he said. Over the eons, small, isolated pockets similar to the harsh early environment have persisted, as have some of the early archaea.

The archaea are believed to have changed very little over time, and it is thought they are the progenitors of the other two kingdoms: the eukaryota and bacteria. For the Honolulu researchers, it made snese that, as in the other two kingdoms, the archaea would have a form of hemoglobin in it, albeit a primitive form. And that's exactly what they found.

"The protoglobins don't bind oxygen for transportation or storage very well," Dr. Alam said. Indeed, the ability to bind and transport oxygen efficiently to tissues that need it is a far more evolved and complex function than what the protoglobins can do. By comparison the structure and function of the protoglobins are quite simple.

Once the protein for the protoglobin was discovered, researchers took their studies to another level and identified the genes for it. "We looked initially for the proteins and then went back to the DNA. We localized the gene," Dr. Alam said.

Now that the genes have been sequenced for the protoglobin, the researchers have applied for a patent and anticipate that the findings can be used in the search for a novel blood substitute.

Knowing how a molecule such as hemoglobin is formed and the specific changes it has undergone in its evolution is useful information when it comes to genetic engineering. Potentially, the molecule can be altered in different ways so it can be either a super-carrier of oxygen, or be used as an oxygen detector. There could be several practical uses for the finding. "Once you have the gene, you can modify that gene," Dr. Alam said. end

* Image is of model of protoglobin found in A. Pernix

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