Glucose oxidation, measuring

Figure 3. Glucose oxidation measured by means of U- C-glucose in hospitalized patients receiving total parenteral nutrition.

The first enzyme biosensor was a glucose sensor reported by Clark in 1962 [194], This biosensor measured the product of glucose oxidation by GOD using an electrode which was a remarkable achievement even though the enzyme was not immobilized on the electrode. Updark and Hicks have developed an improved enzyme sensor using enzyme immobilization [194], The sensor combined the membrane-immobilized GOD with an oxygen electrode, and oxygen measurements were carried out before and after the enzyme reaction. Their report showed the importance of biomaterial immobilization to enhance the stability of a biosensor. 

It has also been shown that LDL oxidation is increased in diabetes. In this connection, Mowri et al. [179] studied the effect of glucose on metal ion-dependent and -independent LDL oxidation. They found that pathophysiological glucose concentrations enhanced copper- and iron-induced LDL oxidation measured via the formation of conjugated dienes. In contrast, glucose had no effect on metal-independent free radical LDL oxidation. Correspondingly,... 

Destruction of nitric oxide by superoxide in the buffers is more likely to account for the short half-life of nitric oxide in vitro. Superoxide dismutase (15-100 U/ml) substantially increased the apparent half-life of EDRF, strongly suggesting that superoxide contributes to the short biological half-life of nitric oxide. In the perfusion cascade bioassay system, the buffers are bubbled with 95% oxygen, contain 11 mM glucose as well as trace iron plus copper contamination and are incubated under the weak ultraviolet (UV) radiation of fluorescent lights. These are prime conditions for the autoxidation of glucose to form small amounts of superoxide in sufficient amounts to account for the short half-life of nitric oxide in nanomolar concentrations. The rate of reaction between superoxide and nitric oxide is 6.7 X 10 M sec L The shortest half-life of nitric oxide measured is approximately 6 sec. To achieve a half-life of 6 sec, the steady state concentration of superoxide would only need to be 17 pM, calculated as ln(2)/ (6 sec X 6.7 X 10 M" sec )-... 

Early glucose monitors measured H202 from Reaction 17-10 by oxidation at a single working electrode, which was held at +0.6 V versus Ag AgCl ... 

Novello F, Me Lean P. The pentose phosphate pathway of glucose metabolism measurement of the non-oxidative reactions of the cycle. Biochem. J. 1968 107 775-791. 

An analogous glucose sensor has been developed by Umana and Waller (1986). Glucose measurement was carried out by reduction of iodine formed from iodide in a molybdate-catalyzed reaction. The current did not reach a stationary value but increased linearly with time. Obviously the main part of glucose oxidation was catalyzed by GOD leached out into the measuring solution. Therefore the sensitivity dropped to 25% of the initial value after 5 measurements and after 10 days the enzyme was completely exhausted. 

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