Wired GOx The study of direct electrical communication between reaction centers of enzymes and electrodes bridges fundamental work on electron transfer through proteins and practical work on biosensors. Itamar Willner and colleagues at The Hebrew University of Jerusalem (Israel), Gesellschaft fur Biotechnologische Forschung (Germany), and the University of Texas at Austin reported a method for assembling an enzyme electrode by reconstituting apo-glucose oxidase (apo-GOx) on a pyrroloquinoline quinone/flavin adenine dinucleotide (PQQ/FAD) monolayer associated with a gold electrode. The resulting enzyme layer efficiently made electrical contact with the electrode and stimulated the electrobiocatalyzed oxidation of glucose. The PQQ/FAD diadlayer exhibited redox waves characteristic of PQQ/ PQQH2 and FAD/FADH2 functions. Integration of the waves by voltammetry showed the presence of 5.5 x 10-10 mol/cm2 of PQQ/PQQH2 and FAD/FADH2, both in excess of the 1.7 x 10"12 mol/cm2 of GOx that can be maximally packed in a monolayer.
GOVERNMENT
First step to screening for endocrine disrupters With a Congressional mandate to proceed, researchers have begun working on a program for identifying endocrine-disrupting compounds that could be responsible for recent reports of physical and reproductive abnormalities in wildlife. On Oct. 31 and Nov. 1, the newly formed endocrine disrupter screening and testing advisory committee (EDSTAC) met in Washington, DC, to create a framework for identifying these hormone-mimicking compounds. EDSTAC is composed of scientists from industry, academia, environmental groups, federal agencies, and labor and water protection groups. The committee's mission is to advise EPA which is taking the lead on this issue, on how to proceed on toxicological testing. The goal is to have a strategy ready for peer review in one year, said Lynn Goldman, head of EPA's Office of Prevention, Pesticides,
Treatment of the the current densubmonolayer with sity was 290 ± apo-GOx produced 60uA/cm2. the reconstituted, The effective electrically conelectrical contact nected, and densely between the packed GOx monoPQQ/FAD-reconlayer. The reconstistituted GOx and tuted GOx monothe electrode suglayer was electrigested minor incally connected terference from with the electrode 0 2 on the amperoby the PQQ redox metric response, relay; and, in the and ascorbate was presence of glunot preferentially cose, electrobiocatelectrooxidized alyzed oxidation of over glucose. The the substrate took transduced curplace whereas the rent densities and PQQ/FAD monoselectivity suglayer alone did not gested that the stimulate oxidation system may be (A) Cyclic voltammograms of (a) GOx of glucose. The useful as an invareconstituted with the PQQ/FAD monoGOx monolayer sive miniaturized produced a current layer bound to the gold electrode and (b) reconstituted enafter adding glucose to a concentration of density correspond- 80 mM; (B) Dependence of the electrooxi- zyme electrode ing to the theoretifor continuous dation current on glucose concentration. cal limit for the monitoring of glumaximum possible turnover rate of 900 ± cose. (J. Am. Chem. Soc. 1996,118, 150 s"1 at 35 °C. The theoretical limit of 10321-22)
and Toxic Substances, the office that will conduct the screening. Calls for certain types of endocrine disrupter testing are contained in Lynn Goldman t h e rece ntly passed Safe Drinking Water Act and the Food Quality Protection Act (Anal. Chem. 1996, 68, 598 A). The Congressional legislation mandates testing for compounds with estrogenic effects on human health and calls for screening of all pesticide active ingredients and certain drinking water contaminants. The wording in the legislation, however, allows EDSTAC to use broader definitions of effects and identify wider classes of compounds. But how much more can be done is not clear, because Congress has set a tight time schedule for any efforts. The screening program must be finalized by 1998, implemented by 1999, and far enough along so that Congress can receive a report in the year 2000.
At the meeting, members of EDSTAC agreed to expand the definition of impact to include ecological as well as human health and seemed ready to also include compounds with androgenic and thyroid effects. Committee members also generally agreed that there would be no single inclusive screen or test but possibly a tiered approach. Goldman said that she also wanted the committee to set priorities on which compounds to screen first. "Our expectation is that the committee would give both science and policy advice [to EPA]," she told them. Goldman urged the diverse group to reach a consensus on a program, but warned, "The agency has the timelines, and we will move ahead without full consensus." EPA is also talking to European governments about endocrine disrupters through the Organization for Economic Cooperation and Development (OECD), a forum for the world's richest countries. The United Kingdom has taken the lead in preparing a paper for review by scientists in OECD countries. Alan Newman
Analytical Chemistry News & Features, January 1, 1997 15 A
