SCIENCE/TECHNOLOGY
Related enzymes catalyze different reactions Two enzymes—mandelate racemase (MR) and muconate lactonizing enzyme (MLE)—that catalyze mechanistically distinct reactions have been shown to be structurally homologous, and thus very likely evol u t i o n a r y related [Nature, 347, 692 (1990)]. This is the first clear example of two enzymes that appear to have evolved from a common ancestor's catalyzing different chemical reactions, according to the chemists who carried out the research. MR and MLE are both part of a biochemical pathway that allows Pseudomonas putida to metabolize aromatic carboxylic acids. MR catalyzes the interconversion of two enantiomers. MLE catalyzes the cycloisomerization of ds,ds-muconic acid to muconolactone by syn addition to a double bond. The research was carried out by Gregory A. Petsko and David J. Neidhart of Massachusetts Institute of Technology, Cambridge; George L. Kenyon of the University of California, San Francisco; and John A. Gerlt of the University of Maryland, College Park. (Petsko has since moved
to Brandeis University, Waltham, Mass.; Neidhart currently is at Abbott Laboratories, Abbott Park, 111.) John Kozarich of the University of Maryland, is also a collaborator on the project. Determination of the crystal structure of MR was facilitated by the discovery of a crystal form of the enzyme in which a single polypeptide chain is the basic repeating unit of the crystal. The crystal structure shows MR is an octamer of identical subunits possessing a symmetry observed previously for MLE. The researchers suggest that this common quaternary structure "reflects the striking similarity of tertiary structure between the subunits of the two enzymes." An analysis of the structural homology between MR and MLE reveals that, of the 358 amino acid residues in a single subunit of MR, 214 (60%) are structurally equivalent to residues in MLE. By comparison, 60% of the residues in the different, but closely related, heme-binding proteins hemoglobin and myoglobin also are structurally equivalent.
Mandelate racemase catalyzes interconversion of two enantiomers... MRN
MR-H
C02~
C02~
C02~
. . . and muconate lactonizing enzyme catalyzes a cycloisomerization reaction
H
H
MR = Mandelate racemase MLE = Muconate lactonizing enzyme
30
November 12, 1990 C&EN
H
H
H
H
Among the 214 structurally equivalent residues in MR and MLE, 64 pairs (30%) are chemically identical. The data strongly suggest that the two enzymes evolved from a common ancestor. The scientists point out that numerous cases are known in which enzymes that catalyze the same chemical reaction on different substrates have arisen from divergent evolution from an ancestral enzyme. This is the first time, however, that structural information has shown that divergent evolution appears to have reworked the catalytic apparatus of an enzyme while maintaining the basic structure of the enzyme. The chemists are working to understand the detailed mechanism of both reactions. Because MR is found only in a subset of the bacteria that produce MLE, it appears possible that MR evolved from MLE. Using site-directed and random mutagenesis, the researchers are attempting to generate MR activity from MLE so as to retrace the evolutionary steps that led from one to the other. Rudy Baum
High-tech microscopes on loan to 15 colleges Two inexpensive scanning tunneling microscopes have been developed and built by scientists from Rochester, N.Y. The scientists plan to loan them for one-month periods to 15 private colleges and universities participating in a chemical education improvement project sponsored by the Charles A. Dana Foundation. Scanning tunneling microscopy may give undergraduates the same concrete grasp of the atomic theory of matter that optical microscopy gave the general public of the germ theory of disease in the 19th century. The STMs were built by physical chemistry professor R. J. Dwayne Miller and graduate student KongGay Loh at the University of Rochester, physicist Howard Mizes of Xerox Corp., and Miller's graduate student Andrew Weissman at Rochester Institute of Technology. Though the cost was only $2000 each, Miller says a combination of innovative electronic filtering and computer pro-
Science/Technology
Novel Materials in Heterogeneous Catalysis EDITED BT
R. Terry K. Baker and Larry L. Mnrrell ACS Syapoetaa Swtoi 437
Novel Materials in
Heterogeneous Catalysis
I
n recent years researchers have begun ex ploring the benefits derived from the use of catalysts prepared in unconventional forms. This new volume reviews this research and highlights the use and availability of new materials in catalysis. It replaces the stereo typed approach to catalysis with one that ex ploits the opportunity afforded from produc ing metal particles by novel routes or by supporting them in unusual locations on a car rier material. Among the topics covered in its 30 chapters are • • • • • •
zeolite materials layered structures clusters ceramic membranes metal oxide catalysts catalysts used in fuel production
A valuable reference for academic and in dustrial scientists in heterogeneous catalysis, including chemical engineers, petroleum re searchers, materials scientists, spectroscopists, ceramicists, and solid-state chemists and physicists. R. Terry K. Baker, Editor, Auburn University Larry L. Murrell, Editor, Engelhard Corporation Developed from a symposium sponsored by the Divi sions of Colloid and Surface Chemistry; Fuel Chemistry; Industrial and Engineering Chemistry. Inc.. and Petro leum Chemistry, Inc. of the American Chemical Society ACS Symposium Series No. 4 3 7 3 7 6 pages (1990) Clothbound ISBN 0 - 8 4 1 2 - 1 8 6 3 - 3 LC 9 0 - 1 2 0 9 $89.95 0 · R · D · Ε · R
F · R · 0 · M
graming produces images of quality equal to those of commercial instru ments costing much more. Along with the STMs, the Roches ter team will loan prepared samples of deoxyribonucleic acid, graphite, tin(IV) sulfide, and liquid crystals. These materials provide good STM images and have significance in cur rent technology. Future plans include a search for funding to pay for STMs for each of the 15 participating schools. The participants in the project are Allegheny College (Meadville, Pa.), Bucknell University (Lewisburg, Pa.), Canisius College (Buffalo, N.Y.), Col gate University (Hamilton, N.Y.), DePauw University (Greencastle, Ind.), Earlham College (Richmond, Ind.), Hobart and William Smith College (Geneva, N.Y.), Ithaca College (N.Y.), Lafayette College (Easton, Pa.), Mt. Holyoke College (South Hadley, Mass.), St. John Fisher College (Roch ester, N.Y.), Swarthmore College (Pa.), Union College (Schenectady,
Physical chemist Miller uses magnifying eyepiece to adjust STM N.Y.), University of Rochester (N.Y.), and Wabash College (Crawfordsville, Ind.). The Dana Foundation funds educational R&D projects at private schools. Stephen Stinson
PFANSTIEHL The Start Of Something Big: Ribonolactone D-Ribono-1. 4-lactone and its 2.3-O-isopropylidene derivative have been the starting points for the synthesis of a wide vari ety of natural products. C-glycosides and carbocycles. We now offer both of these important chiral starting materials, in addition to our wide selection of other sugar lactones. All are available in quantities to meet your needs; research through scale-up. Write or call for a technical brochure and price list and see how Ribonolactone can be the start of something big for you.
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November 12, 1990 C&EN
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