Relay Stations Placed Inside Proteins Can Carry An Electric Current

The body contains several thousand different enzymes that are catalysts for specific bioreactions. Without them, biochemical pathways in the body would not function.

Diabetics have a need for a glucose meter that would show the glucose concentration in the blood at any moment without having to take a sample. If the glucose builds up too much, the meter would send out a signal telling the wearer of the need for insulin.

Glucose gets oxidized with the cooperation of an enzyme called glucose oxidase, which has a molecular diameter of 86 A. Suppose we could immobilize glucose oxidase on an organic semiconductor such as polypyrrole, and the electrons produced when glucose in the blood is oxidized could be brought out through the glucose oxidase to work a meter on the wrist: our aim would be achieved, and diabetics could monitor their condition at any time by a glance at the wrist.10

One could carry this idea further. Since enzymes are so specific in reacting to only certain molecules, one could imagine a future "general diagnoser," a plaque with a series of enzymes adsorbed on microelectrodes that are exposed to the blood, with each able to pick out the molecules that indicate the presence of specific diseases. Oxidation reactions would provide electrons and an electrical signal would indicate the disease through the circuitry, which would identify the enzyme from which the current originated. For such an idea to work, one must have electronic conductivity of

10A wrist glucose meter? Not yet, but several are in development.

the enzyme because eventually the electrons from the reaction on its surface (in contact with the blood) must get through the 10 nm of enzyme to the metallic circuitry of the wrist meter.

Now, most enzymes are centered on a specific redox atom (e.g., Fe) and in order to be oxidized or reduced, the electron, the effector of the act, must travel through the enzyme to the so-called heme group, the vital Fe-containing group, as in hemoglobin, for example.

Enzymes are complex organic substances and are not expected to be good electron conductors at all. If an electron is going to get to and from the heme group to an outside contact, the best hope is quantum mechanical tunneling. However, there is a limit to the jump length in tunneling; it is about 2 nm. Supposing the heme group is in the middle of the enzyme glucose oxidase; then, as it is ~9 nm across, the electron would have to jump ~4 nm, which is not possible.

Adam Heller in 1986 devised and achieved the solution to this, which is illustrated in Fig. 1.12. With his associate, Y. Degani, Heller introduced extra redox centers into

An OR Pt All OR Pt

ELECTRODE ELECTRODE

An OR Pt All OR Pt

ELECTRODE ELECTRODE

Fig. 1.12. Schematic drawing of the glucose oxidase molecule, showing the electron-

transfer distances involved in the various steps of moving an electron from Its two flavin adenine dinucleotide/reduced flavin adenine dinucleotide (FAD/FADH2) centers to a metal electrode. Left: The enzyme before modification. Right: The modified enzyme, after chemical attachment of an array of electron transfer relays ("R"). (Reprinted from Y. Degani and A. Heller, J Phys. Chem. 91: 1286, 1987.)

Fig. 1.12. Schematic drawing of the glucose oxidase molecule, showing the electron-

transfer distances involved in the various steps of moving an electron from Its two flavin adenine dinucleotide/reduced flavin adenine dinucleotide (FAD/FADH2) centers to a metal electrode. Left: The enzyme before modification. Right: The modified enzyme, after chemical attachment of an array of electron transfer relays ("R"). (Reprinted from Y. Degani and A. Heller, J Phys. Chem. 91: 1286, 1987.)

glucose oxidase. The result was duly electrifying—the enzyme became radically more conducting than before.

Supplements For Diabetics

Supplements For Diabetics

All you need is a proper diet of fresh fruits and vegetables and get plenty of exercise and you'll be fine. Ever heard those words from your doctor? If that's all heshe recommends then you're missing out an important ingredient for health that he's not telling you. Fact is that you can adhere to the strictest diet, watch everything you eat and get the exercise of amarathon runner and still come down with diabetic complications. Diet, exercise and standard drug treatments simply aren't enough to help keep your diabetes under control.

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