A Renewed Interest in Immobilized Enzymes
"The years ago, immobilized enzymes were looked on as a panacea for industrial development,' says Lemuel Wingard of the University of Pittsburgh. "There was a lot of enthusiasm, but not much realism.' Realism sank in slowly as investigators learned that enzymes, bound or otherwise, simply could not compete economically with large-scale chemical processes. In specialty areas where enzymes might have been able to compete, as in the production of pharmaceuticals and more expensive chemicals, the desirable enzymes were generally too expensive or, more important, too scarce to be of commercial importance.
That situation is changing rapidly. "In the past couple of years,' says Wingard, "there has been a strong resurgence of interest in immobilized enzymes.' This renewed interest in biological catalysts results primarily from the development of genetic engineering techniques that promise to provide substantial quantities of virtually any desired enzyme at reasonable prices.*
* Modifications of enzymes are discussed in articles appearing in the issues of 13 January, p. 154, and 20 January, p. 269. Preceding articles in this series are cited in those issues. This is the last article of the series.
The technology for immobilizing enzymes is relatively mature (see box). There are, says Wayne Pitcher of Genencor Corporation, "literally hundreds of ways to immoblize enzymes, most of which have been available for some time.' Adds Howard Weetall of Corning Glass Works: "There haven't been any real breakthroughs recently, and there is nothing exciting coming along. The real interest now is in applications of immobilized enzymes.' The key thing now, says Oscar Zaborsky, a consultant who recently retired from the National Science Foundation, "is to come up with new uses and new enzymes that can fill specific needs. If you can find an enzyme that will help you, the chances are that it can be immobilized with some reasonable success.'
Among the number of reasons to immobilize enzymes, the most common is simply to facilitate recovery of the enzyme or separation of the product from the catalyst. Immobilization frequently also stabilized the enzymes. Proteases, for example, catalyze their own destruction; if they are attached to a support, that destruction becomes more difficult. Cross-linking reactions may also stabilize the three-dimensional structure of the protein, rendering it less susceptible to thermal degradation. Immobilization may also make the enzymes less susceptible to oxidation. Ephraim Katchalski of the Weizmann Institute in Israel has shown that the ionic strength of the microenvironment surrounding an enzyme on a highly charged support excludes dissolved oxygen.
The use of enzymes as catalysts seems poised for a remarkable growth. In 1983, enzyme sales worldwide were reported to be about $390 million, up nearly 25 percent from 1979. A 1982 report from the Office of Technology Assessment predicted that, within 20 years, enzymes would be used in the production of $15 billion worth of chemicals and pharmaceuticals. "We are on the verge of a second industrial revolution,' says William Amon, Jr., of Cetus Corporation.
On a dollar basis, about 80 percent of...