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The Yale Alumni Magazine is owned and operated by Yale Alumni Publications, Inc., a nonprofit corporation independent of Yale University. The content of the magazine and its website is the responsibility of the editors and does not necessarily reflect the views of Yale or its officers. |
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The Blue Man Group aside, blue skin is genuinely rare in mammals. Most species can’t even see the color, and all lack the internal ability to produce blue pigments. So those mammals that do get the blues—primates such as the mandrill and the vervet monkey, and marsupials like the mouse opossum—must use a different trick. And so, it turns out, must biologists seeking to account for the lurid color of the mandrill’s face and rump, and the vervet’s and mouse opossum’s scrota. For more than a hundred years, researchers have held that blue skin is blue for much the same reason that the sky is blue. But according to Yale biologist Richard O. Prum, the color experts have “missed something fundamental, and as a result their explanation is just plain wrong.” Unlike pigment molecules, which work by absorbing most of the wavelengths in white light and reflecting back to the eye only a portion of the spectrum, the blue of skin is a “structural” color. The blue of the sky is an example of a particular kind of structural color; its structures are random oxygen and nitrogen molecules in the air that, because of their tiny size, preferentially scatter the shorter wavelengths—the blues and violets—in all directions while allowing the longer wavelengths, the reds, to pass unimpeded. This process is called “incoherent scattering.” But there is another way to create structural color, and writing in the June 15 issue of the Journal of Experimental Biology, Prum and University of Kansas mathematician Rodolfo Torres showed that the blue in mammal skin comes from “coherent scattering.” The best-known examples of this process are the iridescent colors of opals, oil slicks, and soap bubbles. When light hits a layer of a certain material, some of it is immediately reflected by the outermost surface. Another portion of the light enters the material and is reflected back when it hits the bottom surface. If a particular wavelength emerges in phase with its partner in reflection, that color is enhanced; emerging out of phase results in wavelengths cancelling each other out—and no color. In skin, the structures that govern this phase shift are collagen fibers about four millionths of an inch in diameter. Because there’s no iridescence—the color doesn’t change with the viewing angle—and because earlier research had suggested that these fibers were arrayed in random fashion, like the molecules in air, the blue-sky explanation seemed reasonable. But using an electron microscope and a kind of mathematics called the Fourier transform, Prum and Torres showed that the collagen in mandrill and marsupial skin actually possessed what Prum dubbed “quasi-order.” The fibers aren’t packed together in as orderly a fashion as the molecules in a crystal, but they are orderly enough to bring the short wavelengths into phase with each other and create a brilliant blue. Last year, Prum and his colleagues demonstrated that coherent scattering off of more or less ordered collagen arrays accounts for the blue skin of certain birds. Prum has also found that arrays of air bubbles produce coherent scattering in birds' feathers. The researchers are currently examining butterfly wings and dragonfly bodies for signs of underlying order. “We’re finding it everywhere,” says Prum.
The Case of the Missing Proton When you take a sip of lemonade on a hot summer’s day, you may remember learning in freshman chemistry that the sour taste of citric acid comes from molecular rearrangement: a water molecule binds an extra positively charged proton to itself and becomes distinct from the rest of the water molecules in your drink. Mark Johnson, professor of chemistry, is making waves by suggesting that this assumption about how water reacts to the presence of protons may be wrong. Instead of remaining piggybacked on one water molecule, he says, protons might be in constant motion, leaping back and forth like jumping beans over interconnected networks of molecules. The work, which first appeared in the April 29 online edition of Science, could help explain why water appears to be so integral to the origins of life. When Johnson and his colleagues at the University of Pittsburgh and University of Georgia examined the distinctive ways in which water molecules absorb infrared light, they came up with some surprising results. Theoretical models had predicted that when water and protons are combined, groups of 21 water molecules cluster together in open structures (somewhat similar to soccer balls) called “nanocages"; and that each nanocage holds a proton locked onto one water molecule, to form a so-called Eigen ion. The current model posits that the Eigen ion is sequestered securely in the center of the cage. Johnson’s team’s light-absorption experiments confirmed the existence of the dodecahedral (12-sided) cages—but when they looked for the distinctive infrared signature of the proton in the middle, they witnessed an apparent disappearing act. “We went to look for the place where the Eigen ion should give us an absorption, and there was absolutely nothing there,” Johnson says. “So it’s like the case of the missing proton.” Though he isn’t yet sure why the critical proton is absent from the scene, Johnson has started speculating about the possibilities. One scenario is that, like participants in a bucket brigade, water molecules in the nanocage may be constantly shuttling protons among each other. If this molecular flexibility is confirmed in future experiments, it could be one of the factors that make water such an ideal ingredient in biological systems. Proton transport networks, or “proton wires,” as scientists call them, power essential metabolic processes within plant and animal cells, and Johnson and his colleagues are eager to find out how the action of these “wires” is derived from the basic properties of the individual water molecules. In processes like photosynthesis, for instance, water-mediated charge transport may be key in orchestrating the conversion of light energy into energy that’s useful for the plant. “Sometimes embedded water molecules shepherd charge through a cell membrane, and sometimes they form proton wires that pump protons from one side of a barrier to the other,” Johnson says. “Our job is to reveal the rules that govern this action.”
Working for Their Lives Yale researchers have some grim news for older workers: those who lose their jobs near retirement age have more than twice the risk of suffering a subsequent stroke. Using data from the Health and Retirement Survey sponsored by the National Institute on Aging, William Gallo, an associate research scientist at the School of Public Health, and his colleagues tracked 4,220 people who were employed and between the ages of 51 and 61 at the start of 1992. Over the next six years, 457 of these workers, who came from all over the country and all walks of life, lost their jobs due to layoffs or business closings. The remaining 3,763 either remained continuously employed or left the labor force voluntarily. In the May issue of the American Journal of Industrial Medicine, the researchers found that eight of the workers who lost their jobs later suffered from stroke, compared with 67 strokes in the much larger control group. While the number of strokes among those who lost jobs is small, it is statistically significant. Even when adjusted for other risk factors, the risk of stroke for job losers more than doubled. The study is particularly alarming in light of the recent trend toward starting layoffs at the top. “When companies hit downturns they routinely punish the more senior, experienced, and wiser employees because they’re often a little bit more expensive due to seniority pay increases,” says Jeffrey Sonnenfeld, associate dean for executive education at the School of Management. Gallo, however, is not convinced that more layoffs of older workers will necessarily mean more potential stroke victims. “Human beings adapt very easily and very quickly,” he explains. “So the risk may be actually lower in the future.” In the meantime, Gallo urges physicians to ask older patients at risk for stroke about their employment situations. “Increased awareness might help reduce the risk.”
Turmeric and Cystic Fibrosis When he’s not mixing together molecular brews in his laboratory, biologist Michael Caplan can often be found in the kitchen whipping up a curry. He has a heavy hand with the turmeric, a pungent, bright yellow spice that adds a kick to Indian and Caribbean dishes. Recently, Caplan’s lab has also started cooking with turmeric. He has created a new treatment based on the spice that may prove effective in mitigating—even curing—cystic fibrosis (CF), a lethal inherited disorder that affects 30,000 Americans. Caplan and Marie Egan, an associate professor of pediatrics at the medical school, study proteins that send ions coursing through channels in cell membranes. In people with CF, the channels for chloride ions are altered in a way that blocks cells from producing the saltwater needed to clear mucus from the lungs and gastrointestinal tract. Most CF sufferers are born with a mutant chloride channel gene that encodes for a defective protein which cannot reach its proper place on the cell surface. Unable to produce cleansing saltwater, the CF sufferer’s clogged lungs and gut lead to failure to thrive, bacterial infections, and eventually respiratory failure and death, typically by age 30. Two years ago, Caplan found that curcumin, the extract that gives turmeric its bright yellow color, had promising properties. And he already knew from long culinary experience that it was safe, unlike earlier drugs that proved effective but toxic. Caplan tested curcumin in human cells and in mouse models of the disease. The results, reported in the April 23 issue of Science, showed that curcumin undid the protein defect, leading to normal saltwater production in cells and cleared lungs in the mice. Yale has licensed the results of Caplan’s studies to a biotechnology company, which is working in partnership with the CF Foundation to test curcumin in humans. “This is the first time my laboratory has done anything with human applications,” says Caplan; if it works, it will be an extremely impressive debut. |
Noted In a national survey of 1,000 adults conducted between April 26 and May 6 for the School of Forestry and Environmental Studies (FES), 84 percent said the environment would be a factor in how they'd vote in November; 35 percent called it a major factor. Nearly 60 percent rated the quality of the U.S. environment as only fair or poor, and fewer than one in five thought it was improving. The figures were even more negative and pessimistic for the state of the world environment. More than two-thirds of the respondents said the U.S. government should do more to protect the environment. Sixty-six percent of the Democrats and 40 percent of the Republicans wanted action on global warming. Eighty-four percent of all respondents (including 68 percent of the Republicans) called for stricter emissions and pollution standards for business and industry. Politicians should pay attention, says Gus Speth, FES dean. “There’s a huge deficit between the public’s aspirations for environmental protection and what our politics actually delivers.” Nearly three million people worldwide suffer from multiple sclerosis, but exactly how MS destroys nerve fibers has been a mystery. Now, Yale neurologist Stephen Waxman has identified a process that may be the key. Waxman’s team examined damaged nervous system tissue from people who died of a progressive form of MS and discovered abnormalities in the regulation of sodium and calcium that led to nerve cell degeneration. The finding, reported in the May 25 issue of the Proceedings of the National Academy of Sciences, suggests potential strategies to “protect vulnerable nerve fibers,” says Waxman. Using the combined imaging power of NASA’s three “Great Observatories,” a research team led by Yale astrophysicist Meg Urry has uncovered evidence of supermassive black holes near the edge of the known universe. At the June 1 meeting of the American Astronomical Society, Urry discussed how new observatories sensitive to X-rays and infrared radiation revealed black holes at the centers of galaxies formed two billion to five billion years after the Big Bang. |
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