Enzymes in Bioanalytical Chemistry

The enzymes D-amino acid oxidase and lactate dehydrogenase (Eqs. 2.2 and 2.6) have the numbers E.C. 1.4.3.3 and E.C. 1.1.1.28, respectively both are oxidoreduc-tases, and therefore fall into the first of the six main divisions. The enzyme cholesterol esterase catalyzes the hydrolysis of cholesterol esters into cholesterol and free fatty acids (Eq. 2.7), and has been assigned E.C. 3.1.1.13. 

In addition to the E.C. number, the source of a particular enzyme is usually given, listing the species and the organ or tissue from which it was isolated. 

Enzymes can be employed to measure substrate concentrations as well as the concentrations of species that affect the catalytic activity of the enzyme toward its substrate, such as activators and inhibitors. The first known enzymatic assay was reported by Osann in 1845 hydrogen peroxide (H202) was quantitated using the enzyme peroxidase. In 1851, Schonbein reported a detection limit of 1 part H202 in 2 x 106 [i.e., 500 parts per billion] using this method Enzymatic methods 

---

The first applications of enzymes in bioanalytical chemistry can be dated back to the middle of nineteenth century, and they were also used for design of first biosensors. These enzymes, which have proved particularly useful in development of biosensors, are able to stabilize the transition state between substrate and its products at the active sites. Enzymes are classified regarding their functions, and the classes of enzymes are relevant to different types of biosensors. The increase in reaction rate that occurs in enzyme-catalyzed reactions may range from several up to e.g. 13 orders of magnitude observed for hydrolysis of urea in the presence of urease. Kinetic properties of enzymes are most commonly expressed by Michaelis constant Ku that corresponds to concentration of substrate required to achieve half of the maximum rate of enzyme-catalyzed reaction. When enzyme is saturated, the reaction rate depends only on the turnover number, i.e., number of substrate molecules reacting per second. 

---