The method, known as "stable isotope ratio mass spectrometry," can determine where a substance was produced by "weighing" various forms or isotopes of an element in the substance such as the ratio of rare oxygen-18 to common oxygen-16.

Additional uses of the method may result from a new study that challenges the long-held belief that water moves so rapidly through cell membranes and pores that the water inside cells is chemically identical to the water outside cells.

Scientists from the University of Utah in Salt Lake City and Pacific Northwest National Laboratory in Richland, Wash., published the study the week of Monday Nov. 21 in the online edition of the journal Proceedings of the National Academy of Sciences.

The researchers found that up to 70 percent of the water inside rapidly growing bacterial cells was generated by metabolism, the process of converting food into energy and other necessities of life. That conclusion was based on their surprising discovery that water inside the bacterial cells (intracellular water) has a different oxygen-18-to-oxygen-16 ratio than water outside the cells (extracellular water).

"We've shown a significant portion of the water inside the bacteria can come from metabolism of the food and oxygen they consumed," and not from water outside the cell, says University of Utah chemist Eric Hegg, the study's principal author.

If future research proves the same thing is true in mammalian cells, then the difference in isotopic makeup of water inside and outside of rapidly growing cells might be used to detect fast-growing cancer cells in the brain or other hard-to-biopsy areas of the body, or study the metabolism of obese people or people suffering a
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21-Nov-2005