Chappelle, Emmett

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Chappelle, Emmett

AMERICAN BIOCHEMIST
1925–

There are many ways that we could determine if there is life on other planets. The easiest method would be to look for aliens or any of the hallmarks

of civilization. But what if the life-form was microbial? Bacterial life may exist, but would we know it if we saw it?

Emmett Chappelle is a noted biochemist who has, among other accomplishments, devised a method for answering this question. Born on October 25, 1925, in Phoenix, Arizona, he received his B.S. in biochemistry from the University of California in 1950. From 1950 to 1953 he worked as an instructor in biochemistry at Meharry Medical College in Nashville, Tennessee. Chappelle received his M.S. in biochemistry in 1954 from the University of Washington and then returned to California, where he served as a research associate at Stanford University and as a scientist for the Research Institute of Advanced Studies at Stanford. In 1966 he began his work with the National Aeronautics and Space Administration (NASA) as an exobiologist and astrochemist. In 1977 Chappelle moved to the Goddard Space Flight Center as a remote sensing scientist.

His research with Grace Picciolo led to his invention of a method for the detection of adenosine triphosphate (ATP) . The technique takes advantage of the naturally occurring luciferase enzyme and the chemical luciferin. Both are obtained from the lantern of a firefly; hence, this technique is sometimes referred to as a "firefly bioluminescent assay." In combination with ATP and magnesium ions, luciferin and luciferase fluoresce, generating a light intensity that is proportional to the amount of ATP present.

The advantage of fluorescence is that a properly constructed photo-multiplier, under dark conditions, can detect the emission of a single photon , so it is possible to monitor for very low concentrations of ATP. The patented invention outlines how this fluorescence can be used for the detection of bacteria, particularly in a urine sample, thereby speeding the diagnosis of a bacterial infection.

However, such a technique can be applied to any determination of ATP. If extraterrestrial life exists, then there is the possibility that it will employ either ATP or a similar energy molecule. If that energy molecule is introduced into a firefly bioluminescent assay, then light will be produced and it can be measured. The detection of ATP or a similar molecule would be good evidence for the presence of extraterrestrial life.

More recently, Chappelle has been involved in the use of laser-induced fluorescence as a method for determining the health of forest vegetation. The photosystem of green plants uses fluorescence as one way to lose excess energy from absorbed photons, accounting for between 2 and 6 percent of the total absorption. Measuring the amount of fluorescence over a forest allows researchers to monitor the amount of photosynthesis that is occurring. This technique has two significant advantages: First it is nonintrusive and can be used with living plants. Second, it can be performed from within a low-flying airplane, allowing researchers to monitor remote areas.

For his work investigating the biochemistry of life, Chappelle has won numerous awards including NASA's Exceptional Scientific Achievement Medal.