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MID MATTHEY BISHOP, INC. CHEMICALS DIVISION Malvern, Pennsylvania 19355 A Johnson Matthey Affiliate Phone: 215-644-3100
22
C&EN Sept. 5, 1977
the transformed liver cells lack the ability to convert N(OH)AcAF to mutagen; as the ratio of transformed to normal cells increases, enzyme activity diminishes. Again, the most dramatic decreases were found in animals fed corn oil and AcAF. The Texas Tech study shows, Yang says, that enzyme activity that converts a proximate mutagen to ultimate muta The type and amount of dietary fat has gens and probably to ultimate carcinogens a significant effect upon the potency of is responsive to level and quality of di the chemical carcinogen 2-acetylamino- etary fat. Because of the possible effects fluorene (AcAF) in rats, Dr. S. P. Yang, of dietary fats on human carcinogenesis, professor of food and nutrition at Texas he adds, further studies are warranted. Tech University said at a session of the "In particular, a probable correlation Division of Agricultural & Food Chemis between cancer incidence and some try. Generally, rats fed a diet high in corn physical and chemical properties of fats oil, which is relatively unsaturated, were such as the degree of unsaturation, per more susceptible to the carcinogen than oxide number, fatty acid chain length and rats fed a diet high in tallow, which is distribution, position isomerisms of tri more highly saturated. glycerides, and nature of chemical addi Those results, Yang notes, confirm tives should be explored." D various studies—made over the past 30 years—that have shown that rats and mice fed certain vegetable oils were more prone to develop tumors than animals fed Bright future seen for comparable diets containing animal or synchrotron radiation hydrogenated vegetable fats. Yang and his coworkers, pathologist Harry Sproat, biologist Cecil Felkner, and graduate student Carmen Castro, were more con cerned with the relationships between dietary fat and a specific chemical car cinogen. AcAF is a potent hepatocarci- Long the bane of accelerator designers, nogen, Yang says, as is one of its metabo synchrotron radiation—the light emitted lites, ΛΓ-hydroxyacetylaminofluorene. by electrically charged particles whirling AcAF and N(OH)AcAF also are muta at relativistic speeds in the magnetic field gens. Accordingly, a bacterial tester sys of a cyclotron—has begun to transform tem, similar to the Ames test for deter the way work is done infieldsas diverse as mining mutagenicity, was used to quan protein crystallography, mass spectrostify the effects of type and level of dietary copy, and the surface structure of catafats on the metabolism of AcAF in rats. lysts. "Within four years there's going to be In the course of an experiment ex tending over about eight months, groups a large increase in the availability of synof rats received diets containing, var chrotron radiation," says Dr. M. L. Perliously, 5% corn oil, 20% corn oil, 5% tallow, man of Brookhaven National Laboratory, and 20% tallow. Rats were "challenged" organizer of the Division of Nuclear with AcAF, both by intraperitoneal in Chemistry & Technology's symposium on jection and by addition to the diet. Urine the topic. "So we're spreading the word samples were tested for levels of AcAF right now about what scientists can do metabolite. Also, microsome-free frac with it." tions of liver, lung, and kidney tissues The prime sources of this increase, he were examined for enzyme activity, par explains, will be Brookhaven's National ticularly for their ability to form mutagen Synchrotron Light Source, due for comfrom N(OH)AcAF added in vitro. pletion by 1981, and the proposed TanOne finding was that rats fed corn oil talus II machines at the University of diets excreted more N(OH)AcAF in their Wisconsin, Madison. Not only will these urine than did rats receiving comparable facilities contain some of the most powtallow diets. Treatment of rats with AcAF erful synchrotron sources in the world, caused increased enzyme activity, with yielding useful levels of radiation well into the greatest activity found in the group the hard x-ray region, but they will be among the very few sources dedicated receiving 20% corn oil. During the first four months of the ex solely to that purpose. Much of the work with the radiation to periment, there was evidence of changes in the liver cells of all groups, but no pal date has been done in the parasite mode, pable tumors were detected. But after five in which the light is extracted from acmonths, "tumorigenesis was well estab celerators used by elementary particle lished," Yang says, and by the end of the physicists. To the particle physicists the eighth month "the histological impression radiation is a nuisance, the major factor of liver cells in all groups was neoplasia." limiting the energy to which electrons can Consistently, however, the livers of ani be accelerated. (An electron radiates enmals fed corn oil and AcAF were more ergy at a rate proportional to the fourth necrotic and more severely damaged by power of its energy and inversely proportional to the radius of its orbit.) neoplasms. But to scientists tired of the vagaries of As the tumors grew, enzyme activity decreased, Yang observes. Presumably conventional light sources, especially
Dietary fat affects tumor growth in rats
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those for the ultraviolet and x-ray regions, synchrotron radiation is just the thing. Its intensity is stable. It is bright, several orders of magnitude brighter in the x-ray. region than are conventional sources. Its spectrum is broad and smooth, unmarred by the local peaks seen in gas discharges. It is concentrated: Electrons emit radiation as if they had headlamps aimed tangentially to their orbits, and each observer sees the light coming from a point source about 1 cu mm in volume. Andfinally,the light is strongly polarized. Farrel W. Lytle of Boeing Co., Seattle, told the symposium how synchrotron radiation could be combined with the new technique of Extended X-ray Absorption Fine Structure (EXAFS) in studies of the structure of supported metal catalysts. Synchrotron radiation is so bright, he says, that an EXAFS spectrum that took a week to obtain with conventional sources now could be obtained in 10 minutes. To describe the method, Lytle gives the example of a platinum catalyst, highly dispersed through a silica powder and occupying only a fraction of a per cent of the grains' total surface area. How are these platinum atoms arranged, he asks. Are they isolated atoms, thin rafts, or spherical clumps? To find out, he says, measure the absorption of x-rays passing through the material as a function of energy. At the K-edge of platinum—the energy at which the x-ray photon can knock an electron out of the atom's tightly bound inner shell—absorptivity shows a sharp increase. And just above the K-edge the absorptivity exhibits a wiggly fine structure, the EXAFS. In 1971, Lytle and two of his colleagues realized that this phenomenon—known since 1929—was caused by the back-scattering of ejected photoelectrons from nearby atoms. Thus, EXAFS is like a familiar electron diffraction pattern. Mathematical analysis of the fine structure thus reveals the atom's surroundings out to about 5 to 10 A, Lytle continues. In the example of platinum, the atoms are revealed to lie in rafts one or two layers thick on the silica surface. Other experiments performed by Lytle and his colleagues Grayson Via and John Sinfelt of Exxon Research & Engineering, Linden, N.J., include studies of the way gas atoms pack themselves among catalyst atoms, which reveals the symmetry of the chemiabsorption sites, and studies of the geometry of reactants as they interact on the catalytic surface. In another talk, J. P. Smith told the symposium of the work being done at Lawrence Berkeley Laboratory using synchrotron radiation and EXAFS to study metals in biological molecules. Since the energy of each element's K-edge is unique, he says, the signal can't be masked by temperature effects, oxidation states, or signals from other elements. Candidates for study by this method are molybdenum in the enzyme nitrogenase, for which no other probe is adequate, and magnesium in chlorophyll. D
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