and amino, share the common ability to donate electrons to appropriate acceptors. This is in accordance with the observation made by Dr. A. SzentGyorgyi and co-workers at the Institute for Muscle Research, The Marine Biological Laboratory, Woods Hole, Mass., in 1960, that carcinogenicity of aromatic hydrocarbons is correlated with their ability to form charge -transfer complexes with local acceptors. But charge transfer is not the only criterion for cancer-inducing properties of compounds, Dr. Huggins says. For example, a number of hydrocarbons that can donate electrons— indole and phenanthroline, for example—are noncarcinogenic. Geometry. The molecular similarity of carcinogens and steroids was pointed out previously by Harvard's Dr. Louis F. Fieser, Dr. Huggins notes. However, the Chicago scientists have extended a study of this geometric similarity to include the purine and pyrimidine base pairs—for example, guanine/cytosine and adenine/thymine—of nucleic acids. They made a molecular model of the base pairs guanine/cytosine' and constructed a frame around it. Models of all the known aromatic carcinogens as well as models of steroids such as testosterone and progesterone can be inserted within this frame. They thus show the similarity in geometric pattern among the three classes of compounds—carcinogenic aromatics, steroids, and base pairs of nucleic acids. This geometric similarity underlies Dr. Huggins' and Dr. Yang's theory. It is already known that nucleic acids consist of two helical, intertwined polynucleotide strands. Hydrogen bonding occurs between pyrimidine and purine bases on opposite strands. If the helix were unraveled, it would resemble a ladder, the linked base pairs resembling the rungs. Carcinogenic aromatics—like the base p a i r s are planar and have identical thickness (3.6 A.); they could fit perfectly within the ladderlike frame. Steroids, being thicker (5 to 6 A.), could not. This may explain why steroids are not carcinogenic, the Chicago scientists believe. To induce cancer, therefore, it seems that hydrocarbons must not only be electron donors, but must also closely resemble the base pairs of nucleic acids in solid geometry, Dr. Huggins says. The recipient of the charge transfer isn't known; but very probably it's a nucleic acid, he adds.
Trypsin Can Function in Anhydrous Medium Evidence shows trypsin acts as a catalyst in pure dimethyl sulfoxide, indicates reaction path Trypsin shows catalytic activity in pure dimethyl sulfoxide, according to chemists at Adelphi College, Garden City, N.Y. The Adelphi workers find that crystalline trypsin reacts with p-nitrophenyl acetate in pure dimethyl sulfoxide, and have followed the reaction spectrophotometrically. They have also found that trypsin exhibits proteolytic activity in mixtures containing 95% dimethyl sulfoxide and 5% water. The reaction between trypsin and p-nitrophenyl acetate in dimethyl sulfoxide may throw some light on the reactive site of the protein, say Adelphi's Dr. Frederick A. Bettelheim, Kenneth Smith, and Dr. Aaron Lukton (now at Brooklyn College). Their spectrophotometric data give evidence of a two-step reaction between trypsin and the nitrophenyl acetate in dimethyl sulfoxide. First, there is a shift of the enzyme peak from 280 m/x to longer wave lengths. This shift is very rapid, indicating a fast first step in the reaction. Then peaks at 320 and 432 m^ gradually appear; these indicate that
a much slower second step takes place. The peaks at 320 and 432 m^ correspond to the liberation of p-nitrophenol. In experiments using equimolar concentrations of enzyme and substrate, the amount of p-nitrophenol liberated shows that the reaction is complete. The shift in the 280 m{x peak indicates that a rapid intermediate formation may occur between the enzyme and the substrate, p-nitrophehyl acetate. This probably involves the tyrosine group of trypsin, Dr. Bettelheim says. Not only does the enzyme peak shift toward longer wave lengths, but its intensity also decreases. Since the absorption coefficient of the intermediate is not known, it's not certain that the absorption decrease is caused by a decrease in concentration of the intermediate complex, he adds. The Adelphi chemists have tried to isolate the intermediate by precipitating it from dimethyl sulfoxide with an excess of ether, but were not successful as both the precipitate and filtrate
ENZYME. Dr. F. A. Bettelheim uses a spectrophotometer to study the reaction between trypsin and p-nitrophenyl acetate in dimethyl sulfoxide. The data obtained from the Adelphi College work give evidence of a two-step reaction path, and aid in determining the reactive site of the enzyme MAY
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gave UV peaks at only 280 and 320 m/x. It's possible that in the dif ferent solvent the equilibrium shifts, and the complex which shows the en zyme peak shift is not stable, Dr. Bettelheim says. On long standing (24 hours or more), the shifted en zyme peak returns to its original 280 τημ position—more evidence for the intermediate's instability. Evidence that the reaction involves transacetylation was provided by label ing the acetate group of p-nitrophenyl acetate with carbon-14 and observing the activity in the isolated enzyme after precipitation from the reaction mixture. To get a clue to the surface site involved in the p-nitrophenyl acetate-trypsin reaction, the Adelphi group also used acetylated trypsin. It showed the same reaction pattern as the nonacetylated one, implying that the transacetylation is not on trypsins' secondary amino groups. Intermediate. Dr. Bettelheim be lieves that the interaction between pnitrophenyl acetate and trypsin in di methyl sulfoxide proceeds through the formation of an intermediate, possibly near the tyrosine of the enzyme sur face. In recent work, Dr. J. F. Wootton and Dr. G. P. Hess of Cornell Uni versity [JACS, 84, 440 (1962)] give spectroscopic evidence that the inter action of α-chymotrypsin with sub strate in water causes structural changes of the enzyme resulting in perturbation of the tryptophane spectrum of chymotrypsin. The nature of the actual bond forma tion in the trypsin-p-nitrophenyl ace tate reaction is unknown. The inter mediate slowly transfers the acetyl group to a more permanent position on the enzyme surface group with the simultaneous evolution of p-nitrophenol. Thus the primary site acts as a catalyst, as is apparent by the dis appearance of spectral evidence of the intermediate at the end of the reac tion. Partial acetylation of the second ary amino groups on the trypsin sur face does not influence the catalytic potential, Dr. Bettelheim says. Other workers have shown that trypsin has esterase activity in dioxane-water mixtures containing 88% dioxane. Experiments by the Adelphi group show that trypsin exhibits ac tivity as a proteolytic enzyme in di methyl sulfoxide-water mixtures con taining as high as 9 5 % dimethyl sulf oxide. These studies aid in determin ing the reactive site of the enzyme, Dr. Bettelheim says.
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How to select the best BENTONE® gellant for any organic system Use this " F a n " to simplify the job . . • help you m a k e the most efficient m a t c h ! There are three Bentone gellants. All three offer outstanding advantages in performance and economy. But, for any particular application, only one provides most efficiency, most economy. The Bentone Gellant Selection Fan helps you choose that one. The fan is simple to use and is largely self-explanatory where individual organic liquids are concerned. Where a system contains a mixture of or-
ganic liquids, a "weighed average" polarity for the whole system will have to be estimated. The fan will then help you choose the right Bentone gellant for the job. The fan is arranged with highest polarity liquids on the left and lowest polarity liquids on the right. The liquids nearer the fan on each vertical line are generally more readily and efficiently gelled than those higher up.
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For a complete listing of these and other products, see Pages 360A through 360L of the 1962 Chemical Materials Catalog.
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BRIEFS The behavior of explosives between 300° and 1000° C. can now be measured by a technique developed in the U.S. Naval Ordnance Laboratory's organic chemistry division at White Oak, Md. The new method determines decomposition rate of an explosive by noting the time that it takes for a tube filled with explosive to explode when heated to a specific temperature. The NOL scientists use the thin, stainless-steel tubing of a hypodermic syringe, which can be heated almost instantaneously. Temperature at time of explosion can be calculated from its significant temperature coefficient of resistance. Data gleaned from the "hot tube'"' tests are helping NOL scientists to learn how to control the sensitivity of explosives.
Rifamicine SV, an antibiotic developed in Italy, is now being sold there. Trade-named Rifocin by Lepetit, S.p.A., the antibiotic was isolated from a strain of Streptomyces mediterranei in 1957. It's active against a wide range of gram-positive cocci, including some staphylococci resistant to other antibiotics, Lepetit says.
Removal of thin surface layers of metal crystals improves the metal's strength significantly, according to Dr. Irvin R. Kramer, principal scientist at Martin Co.'s space systems division, Baltimore, Md. Aluminum crystals— 99.997% pure, 4 inches long, and 1 / 8 inch thick on each side—were slowly etched electrolytically while being stretched in a device to determine tensile strength. Dr. Kramer says that imperfections collect in a very thin layer at the metal's surface. Removing this layer changes strength, plasticity, and fatigue life of the metal.
A crystal chemistry section has been set up at the National Bureau of Standards, Washington, D.C. The new section is directed by Herbert Steffen Peiser. The section will b e involved in studying methods of crystal structure determination. Research will also be done on correlating known crystal structures, developing new theories, formation and transformation mechanisms of crystalline order, and disorder phenomena.
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