Science Concentrates

Estrogen-like chemicals cause prostate defects in mice

Male mice exposed in the womb to very low levels of estrogen-like chemicals found in oral contraceptives and food containers develop deformities in the prostate and urethra (Proc. Natl. Acad. Sci. USA 2005, 102, 7014).

Researchers at the University of South Dakota School of Medicine and the University of Missouri exposed pregnant female mice either to doses of bisphenol A (shown, left) below levels usually found in pregnant women or to low doses of ethynylestradiol (right). The exposed male fetuses developed more ducts in their prostates and a narrowing of the urethra. If human fetuses respond similarly to these chemicals--and many studies indicate that they do--this research may explain the rapid rise in prostate cancer and bladder problems, the authors say.

Bisphenol A, first shown to mimic estrogen in the 1930s, is the monomer used to manufacture polycarbonate food containers and the linings of almost all metal food and beverage cans. It leaches from polycarbonate, especially in microwave ovens, says study author Frederick S. vom Saal of the University of Missouri. When women become pregnant while on birth control pills, their fetuses are exposed to higher doses of ethynylestradiol than were used in this research, he says.

Calculations point to more stable enzymes

Researchers have devised a computational approach to stabilizing enzymes at higher temperatures while preserving catalytic efficiency (Science 2005, 308, 857). The goal is a longer "shelf life" for enzyme reagents that doesn't sacrifice activity at ambient temperature, says team leader Barry L. Stoddard of the Fred Hutchinson Cancer Research Center, Seattle. In the calculations, residues known to participate in substrate binding and catalysis, as well as their immediate structural neighbors, are held constant, but all other amino acids are fair game for change. In the case of yeast cytosine deaminase, by changing three amino acids, Stoddard and coworkers achieved a 30-fold increase in the half-life of the enzyme at 50 °C without decreasing catalytic efficiency at lower temperatures. The computational strategy for designing more thermally stable enzymes should work for any enzyme with a high-resolution crystal structure and well-known active site, Stoddard says.

HOOO radical characterized

The HOOO radical, which has been implicated in atmospheric processes, has been structurally characterized (Science, published online May 5, dx.doi.org/10.1126/science.1112233). HOOO is thought to form in the atmosphere via the reaction of an OH radical and O₂. But atmospheric HOOO has proven difficult to detect, in part because the radical has been poorly characterized experimentally. In the hopes of collecting experimental data on HOOO that could be used for atmospheric detection, Yasuki Endo, Kohsuke Suma, and Yoshihiro Sumiyoshi at the University of Tokyo used a Fourier transform microwave spectrometer to record rotational spectra of the HOOO radical. From these spectra, they conclude that HOOO has a trans planar structure and that the central HO-OO bond is fairly long (1.688 Å). The authors say these data will allow them to calculate wave transitions that could be used to search for the radical and probe its potential role in the atmosphere--as a sink of atmospheric OH radicals, for example.

Healthy oils turn toxic in the fryer

When it comes to deep frying, highly unsaturated vegetable oils, such as soybean, sunflower, and corn oils, may soon lose their reputation as healthy alternatives to saturated animal fats and partially hydrogenated oils. Unlike their saturated counterparts, these vegetable oils haven't been shown to increase levels of bad cholesterol, and they've been considered heart-healthy because they contain high levels of linoleic acid. Now, food chemists A. Saari Csallany and Christine Seppanen report that when these oils are heated at frying temperatures (365 °F) for 30 minutes or longer, the healthy linoleic acid oxidizes to the highly toxic compound (2E)-4-hydroxy-2-nonenal (HNE, shown). This toxic aldehyde has been linked to a number of diseases, including Parkinson's and Alzheimer's. The University of Minnesota researchers also found that the concentration of HNE in fried food is directly proportional to its concentration in the cooking oil. The toxin accumulates with each heating cycle, underscoring the importance of not reusing these oils for frying. The work was presented on May 4 at the American Oil Chemists' Society meeting in Salt Lake City.

Cadmium at enzyme's center

The first metalloenzyme containing cadmium has been purified from the marine diatom Thalassiosira weissflogii (Nature 2005, 435, 42). Mak A. Saito of Woods Hole Oceanographic Institution, Todd W. Lane of Sandia National Laboratories, and colleagues purified and sequenced the novel cadmium-containing carbonic anhydrase (an enzyme involved in CO₂ fixation during photosynthesis) from T. weissflogii grown in seawater. X-ray absorption near-edge spectroscopy of the purified enzyme confirms the presence of a cadmium-binding site. Comparison of the enzyme's spectra to those of model cadmium compounds suggests that, in the enzyme, cadmium has a roughly tetrahedral geometry and is bound by two or more thiolates. Another recently sequenced diatom also carries a gene for a similar enzyme, suggesting that cadmium carbonic anhydrases might be widely distributed in oceanic microbes, Saito says. Such a biological requirement for cadmium metalloenzymes may explain why the distribution of cadmium in the ocean closely resembles that of major nutrients such as phosphate, he notes.