Lactate 2-monooxygenase, reaction

Two enzymes are commonly used for amperometric biosensors, namely lactate oxidase (LOD) and lactate dehydrogenase (LDH). It should be noted that, in this instance, LOD refers to the enzyme which catalyses the reaction shown in Fig. 23.4, in which the products are pyruvate and H202. This type of enzyme was formerly assigned the E.C. number 1.1.3.2, but this was confused with lactate monooxygenase (E.C. 1.13.12.4), which is also commonly referred to as type I lactate oxidase [55] or simply lactate oxidase [56] whose products are acetate, C02 and H202. The LOD which catalyses the reaction shown in Fig. 23.4 has also been referred to as type II lactate oxidase [55] following clarification of this point in a published letter [57], current publications refer to this enzyme as E.C. 1.1.3.x. 

With a constant of K = 2.7640-5 mol/1 (pH 7.0, 25°C) the equilibrium of the LDH-catalyzed reaction lies far to the lactate side. This means that whereas for lactate sensors based on LDH the forward reaction has to be forced by alkaline buffer and pyruvate- or NADH-trapping agents, the reduction of pyruvate proceeds spontaneously under normal conditions. This direction of the reaction has been used in a sequence electrode for pyruvate assay (Weigelt et al., 1987b). In the presence of lactate monooxygenase (LMO) lactate formed from pyruvate by LDH is oxidized by molecular oxygen, the consumption of which was indicated at a Clark-type electrode. The enzymes were immobilized in a gelatin membrane. Of course such a sensor measures the concentration of lactate in the sample, too. Therefore it is suited to the determination of the lactate/pyruvate ratio, which is a clinically important parameter. Pro-... 

During this coupled reaction in the membrane large amounts of lactate and oxalate are formed which can be indicated by coupled lactate monooxygenase or oxalate oxidase. Using lactate monooxygenase an amplification factor for NADH of 220 was obtained. 

L-lactate monooxygenase (LMO) catalyzes the reaction of L-lactate with O2, producing acetate, CO2, and H2O (Equation (7)). 

The determination of lactate is important in medicine, because certain disorders are related to lactic acidosis, and in industry, for the control of milk and other food products. A lactate sensor can be constructed by coupling amperometric transducers with various enzymes, such as lactate dehydrogenase, cytochrome b2, lactate oxidase and lactate monooxygenase. Lactate dehydrogenase requires NAD as a cofactor, whereas cytochrome b2 uses potassium ferricyanide, which is much cheaper [173]. Cytochrome b2 catalyses the following reaction ... 

---