Enzyme metabolizes C-F bond 3-Fluoromuconic acid and 3-fluorocatechol are formed in the metabolism of 2-fluorobenzoic acid by a microorganism, Pseudomonas species. The conclusion results from research on carbon-fluorine bond metabolism by Dr. Peter Goldman of the National Institutes of Health, Bethesda, Md. There is increasing interest in the nature of the carbon-fluorine bond because of the frequent increased biological activity of fluorine analogs over naturally occurring compounds. A number of biochemical analogs— fluorocitrate and fluorouracil, for example—owe their action as specific enzyme inhibitors to a similarity in size between the hydrogen and fluorine atoms. These features make compounds containing the carbon-fluorine bond a potential source of new metabolic inhibitors and perhaps pharmacological agents. Dr. Goldman and his coworkers, G. W. A. Milne and Maria T. Pignataro, say their data suggest that the two possible metabolic reactions for 2-fluorobenzoic acid can be catalyzed by the same enzyme [Arch. Biochem. Biophys., 118, 178 (1967)]. The acid may undergo oxidative decarboxylation followed either by removal of fluoride to yield catechol or by retention of fluorine to yield 3-fluorocatechol. Before these experiments, Dr. Goldman had isolated an enzyme (from a pseudomonad in Potomac River mud) which is capable of carrying out the stoichiometric conversion of fluoroacetate to glycolate and fluoride. According to the NIH chemist, this conversion differs from previous carbon-fluoride bond breakages. With the new enzyme, the fluoride is released from an aliphatic carbon rather than from an aromatic ring, as in the action of phenylalanine-hydroxylating systems on pfluorophenylalanine. Also, the hydroxy! group of the glycolate is derived from water rather than from atmospheric oxygen. . Dr. Goldman believes the dehalogenation reaction is irreversible. The overall reaction seems to be irreversible because no significant oxygen-18 was found in glycolate after the incubation of glycolate and fluoride in H 2 1 8 0 . He proposes the name haloacetate haliodohydrolase for the enzyme catalyzing the reaction. In the reaction mechanism proposed by Dr. Goldman, a sulfhydryl group on the enzyme displaces the fluoride ion to form acetate in a thioether linkage to the enzyme. The second step can be envisaged as a hydroxyl group displacing the enzyme with the formation of glycolate. The first step in the mechanism is supported by the nonen28 C&EN FEB. 6, 1967
zymic removal of halides from iodo-, bromo-, and chloroacetic acids (at slightly alkaline pH) by glutathione to yield a thioether. Dr. Goldman performed another experiment to show that the dehalogenation is irreversible. If the reaction were reversible, the exchange of isotope between chlorine-36 and chloroacetate would be expected. There was no exchange, however, proving irreversibility of the first step.
Scrapie agent stirs debate A small viruslike agent that just might turn out to be solely a protein is stirring up a vigorous debate among virologists. It all revolves around the sheep disease known as scrapie and the chemical nature of the agent that transmits the disease to the nervous tissue of other animals. The implications are broad, and tangled. For finding the right answers could help clear up several questions about the human disease, multiple sclerosis. It could also sharpen perspective on some diseases that seem to have both genetic and infectious origins. The controversy distills to this: Americans think the agent is a virus; the British think it's a protein. Both qualify their claims in the conventional ways, but they do form two schools. The most recent development was a report in Veterinary Research for Jan. 7 by Iain H. Pattison and Katharine M. Jones of the Institute for Research in the Animal Diseases, Compton, England. What they did, essentially, was extract the scrapie factor from the brains of infected goats, rats, and mice, using methods common for protein separation. The technique involved chloroform-methanol, sodium chloride, and picric acid precipitation. Reextracted factor, washed several times with water, induced the disease in normal animals of the same species. These findings should send American investigators scurrying to their labs in attempts to repeat the work. Up to now, many have complained about the unrepeatability of previous British work and of the dubious interpretations based on impure extracts. The American argument runs generally along lines that the factor behaves, despite some anomalies, like a virus in the animal system. The confusion is sustained by a lack of serological techniques that could be used to follow the agent's course and by the failure of scientists to develop tissue cultures that will support the agent. Until these needs are filled, they say, really definitive studies are impossible. Doing a great deal of the American work in the field are William Hadlow
The late Georgette Kuru, others under attack
of the Public Health Service's Rocky Mountain Laboratory in Hamilton, Mont., Hilary Koprowski of the Wistar Institute in Philadelphia, and the National Institutes of Health group of Dr. Carleton Gajdusek, Clarence J. Gibbs, and Michael Alpers. Besides the U.K.'s Pattison and Jones, a team is working at the Moredun Institute in Edinburgh, Scotland. (The NIH group is working with the human disease, kuru, induced in a series of chimpanzees, starting with an animal, now deceased, by the name of Georgette.) All of these scientists see the scrapie work in terms of a model for detailed studies of multiple sclerosis and other so-called slow-acting viral diseases that affect animals and humans. Whatever their differences, both sides do agree that the scrapie factor is peculiar. It resists inactivation by boiling. Scrapie brain tissue preserved several months in formalin, normally an inactivator, yields an active agent. The factor elicits no antibody response in infected animals. Neither ribonuclease, which tears down virus nucleic acid, nor trypsin, which disassembles protein, affects it, the British say. Ultraviolet radiation, say the British, doesn't hurt the factor as it does most viruses. Attempts to view it under the electron microscope have failed. The British have used the UV and ribonuclease data as evidence for the agent's protein nature, but the U.S. school says many factors could account for the results and not rule out the virus theory. The results of the next round are anybody's guess. But the fascination remains. Scrapie, multiple sclerosis, and kuru, a New Guinea disease similar to multiple sclerosis and under study at NIH, are under growing attack. And the gut answers seem on the verge of coming in. It may be that the mechanism is so tied up with protein and nucleic acid synthesis that both sides are right.
