Notebook

MAD LEMURS A study of lemurs infected with bovine spongiform encephalopathy (BSE), clarifies the pathogenesis of the abnormal proteinase-resistant protein (PrP) or "prion" protein now thought to cause encephalopathic diseases. Also, more zoo animals could have the disease than previously thought (N. Bons et al., "Natural and experimental oral infection of nonhuman primates by bovine spongiform encephalopathy agents," Proceedings of the National Academy of Sciences, 96:4046-51, March 30, 1999). The study, which involved more than two dozen experimentally and spontaneously infected lemurs in France, confirms expectations from previous research about prion distribution and brain degeneration, explains National Institute of Neurological Disorders and Stroke (NINDS) researcher Paul Brown, senior author of the report. The 20 lemurs that were spontaneously infected came from three different French primate centers and were all fed beef protein dietary supplements made by a British company. Presumably, the researchers concluded, the beef used--cracklings or the "fifth quarter of beef" suitable for human consumption--was contaminated with BSE. However, Brown notes, the specifics of the ingredients have not been "exactly" verified. "We stated everything we could find out, and if that was accurate I guess that means that beef 'fit for human consumption' was still probably contaminated and that's not particularly good news," he says. It may mean, he adds, the precautions placed on beef by the British government a few years back following the "mad cow disease" outbreak "wasn't quite enough." Or, he muses, "it may mean that lemurs are far more susceptible to BSE than humans are. That is a possibility." --A.J.S. Rayl GOLGI DIGGERS The Golgi apparatus was discovered in 1873, when Italian histologist Camillo Golgi stumbled upon it while looking for a way to stain neurons. So unsure was he of the nearly transparent "internal reticular apparatus" that he didn't report it until 1898. Now researchers from the University of Chicago have used the jellyfish marker molecule green fluorescent protein (GFP) to illuminate the organelle's origin (O.W. Rossanese et al., "Golgi structure correlates with transitional endoplasmic reticulum organization in Pichia pastoris and Saccharomyces cerevisiae," The Journal of Cell Biology, 145:69-81, April 5, 1999). The Golgi adds sugars to proteins arriving from the endoplasmic reticulum (ER). The organelle forms from nearby ER, creating a continuous secretory network. Because of this association, the researchers hypothesized that species with strikingly different Golgi apparati would also show differences in their ER. Two types of yeast provided the answer--Pichia pastoris, which has distinct Golgi stacks next to the ER, and Saccharomyces cerevisiae, which has scattered Golgi membranes. "The difference in Golgi organization between Pichia and Saccharomyces gives us an experimental tool to understand how Golgi stacks are constructed," says Benjamin Glick, assistant professor of molecular genetics and cell biology. Hooking GFP to proteins normally found at the interface between the Golgi and ER revealed very different fluorescence patterns for the yeasts. The "transitional" ER in Pichia lit up in a few discrete sites, whereas Saccharomyces' ER showed up as 30 to 50 spots, throughout the cell. What does it all mean? No one knows. "Presumably, most eukaryotes take the trouble to organize their Golgi systems because this promotes efficiency. Yet, somehow, Saccharomyces manages to grow very happily," explains Glick. The researchers plan to disrupt the Golgi organization in Pichia to probe the importance of having neat stacks. --Ricki Lewis FOLIC ACID MECHANISM REVEALED The effects of vitamin deficiencies are often realized long before they are understood, and this has certainly been the case with folic acid, known to protect against neural tube defects (NTDs) and cardiovascular disease. The Food and Drug Administration recently upped requirements to 400 micrograms daily for adults and 600 for pregnant women, although the mechanism remained unknown. Now, a team from the University of Michigan in Ann Arbor and Montreal Children's Hospital has described the activity of the enzyme that a folic acid derivative activates, revealing the role of the vitamin (B.D. Buenther et al., "The structure and properties of methylenetetrahydrofolate reductase from Escherichia coli suggest how folate ameliorates human hyperhomocysteinemia," Nature Structural Biology, 6:359-65, April 1999.) The enzyme, MTHFR, catalyzes conversion of homocysteine to methionine. When folic acid is deficient, so is the enzyme, and homocysteine accumulates, adversely affecting health. The researchers obtained an X-ray structure of the E. coli version of the catalytic portion of MTHFR, because the human version is difficult to crystallize. The portrait revealed an area near the bottom of a barrel-like structure that binds FAD, a cofactor. Mutation, or lack of folic acid, destabilizes this crucial binding. Adding folic acid to E. coli MTHFR in vitro, or to crude extracts of human lymphocytes, stabilized FAD binding. "Having a notion about the mechanism helps to make sense of the empirical observations. Our results support and reinforce the FDA guidelines," says Martha Ludwig, a professor of biological chemistry at the University of Michigan. Particularly interesting is the fact that 10 percent of the population produces an inefficient enzyme, causing mild homocysteine excess. The prevalence suggests an associated benefit, which might be protection against chromosome breakage. --Ricki Lewis ISOFLAVONES ONLINE Researchers and the general public can turn to the World Wide Web for the lowdown on phytoestrogen content in the diet. Researchers at the U.S. Department of Agriculture and Iowa State University have posted the isoflavone content of 128 foods. The foods range from beans, chick peas, and lentils to tempeh and tofu. The foods also include brand names such as Green Giant Harvest Burgers. The database, assembled from about 30 research reports, gives information on three isoflavones: daidzen, genistein, and glyciten. These compounds have been linked in scientific and popular literature to protection against a variety of illnesses, including cancer, heart disease, and osteoporosis. The database is designed to help researchers get valuable answers on the role of isoflavones. It is a tool that can be used "to hopefully make some major steps forward in answering the question of whether isoflavones and their estrogen or antiestrogen activity is important in health," says Gary Beecher, a research chemist in the USDA's Food Composition Lab, and one of the database developers. The database can be found at www.nal.usda.gov/fnic/foodcomp/Data/isoflav/isoflav.html. A similar database on carotenoids (www.nal.usda.gov/fnic/foodcomp/Data/car98/car98.html) was established last fall. One on food flavonoids is projected. "One of the reasons we compile data and put them together in databases is to allow health professionals to associate the intake of specific components with the incidence or risk of disease. Without such databases the best that health professionals can do is associate food intake with risk of disease, says Beecher. By providing more specific and detailed information, the databases will offer higher quality scientific information on the link between diet and health, says Beecher. --Harvey Black GRAPEFRUIT POWER Washing down certain meds with grapefruit juice may not be such a great idea after all. A series of studies, starting with a 1991 paper in Lancet (D.G. Bailey et al., "Interaction of citrus juices with felodipine and nifedipine," Lancet, 337:268-9, 1991), found that drinking grapefruit juice helps the body absorb several orally administered drugs by decreasing the levels of a drug molecule-degrading intestinal enzyme known as cytochrome P45 3A (CYP3A). Only grapefruits and a few other known natural agents, such as black pepper, have been shown to affect the CYP3A enzyme via an as-yet unidentified compound. But a new study, done in vitro, suggests that this is only the case for certain medications (A. Soldner et al., "Grapefruit juice activates P-glycoprotein-mediated drug transport," Pharmaceutical Research, 16:478-85, April 1999) and that in the case of several other drugs, the juice may actually have the opposite effect. "It could definitely be a problem with certain drugs," says study director Leslie Benet, a professor of biopharmaceutical sciences at the University of California, San Francisco. Benet emphasizes that the effect is not minor: Grapefruit juice has been shown in previous studies to increase the magnitude of absorption of some drugs by as much as four or fivefold. The drugs that were inhibited include the cancer drug Vinblastine, the blood pressure drug Losartan, the allergy drug Fexofenadine, and Digoxin, which is used to treat congestive heart failure. Benet's group will try to confirm the in vitro findings in an upcoming clinical trial. --Eugene Russo MUSHROOM WASH Biotechnologists have coaxed bacteria to produce indigo to make blue jeans blue. A team from Novo Nordisk Biotech Inc., in Davis, Calif., borrowed a peroxidase from inkcap mushrooms, and unleashed it in the wash, where it removes stains. Peroxidases typically come from plants such as horseradish and soybean, but these don't stand up well to expression in other species. So the researchers turned to the fungal kingdom. "This was the only peroxidase that was expressed at sufficiently high levels for commercialization," says Joel R. Cherry, project leader for directed evolution at the company. Using information from the X-ray crystal structure of the peroxidase, the researchers identified key areas to alter by site-directed mutagenesis so that the enzyme could withstand the high heat, oxidation, and pH in a washing machine. To ease screening, they cloned the retooled mushroom genes in yeast, auditioning them in an environment mimicking the inside of a wash. Survivors won, the best 100 times more resistant to oxidation than the natural enzyme and 174 times more stable at high temperatures. But a launderer need not toss mushrooms and yeast into the washer. The peroxidase "is an additive, just like the proteases and lipases and cellulases that are currently added to detergents. It is supplied to the detergent makers as a granulate," concludes Cherry. --Ricki Lewis

Notebook

Interested in reading more?

Become a Member of