Enzyme loading factor

Laval etal. (1984) bound LDH covalently to electrochemically pretreated carbon. The enzyme was fixed by carbodiimide coupling simultaneously with anodic oxidation of the electrode surface. The total amount of immobilized LDH was determined fluorimetrically after removal from the electrode and hydrolysis. The authors found that at a maximal enzyme loading of 13 pmol/cm2 six enzyme layers are formed. The immobilization yield was about 15%. The kinetic constants, pmax and. Km, were not affected by the immobilization. The obtained enzyme loading factor of 10-3 indicates that diffusion in the enzyme layer was of minor influence on the response of the sensor. The layer behaved like a kinetically controlled enzyme membrane, i.e., the NADH oxidation current was proportional to the substrate concentration only far below Km- With increasing enzyme loading the sensitivity for NADH decreased due to masking of the electrode surface. 

ADP AFP ab as ALAT AP ASAT ATP BQ BSA CEH CK CME COD con A CV d D E E EC ECME EDTA EIA /e FAD FET FIA G GOD G6P-DH HBg HCG adenosine diphosphate a-fetoprotein antibody antigen alanine aminotranferase alkaline phosphatase aspartate aminotransferase adenosine triphosphate benzoquinone bovine serum albumin cholesterol ester hydrolase creatine kinase chemically modified electrode cholesterol oxidase concanavalin A coefficient of variation (relative standard deviation) layer thickness diffusion coefficient enzyme potential Enzyme Classification enzyme-chemically modified electrode ethylene diamine tetraacetic acid enzyme immunoassay enzyme loading factor flavin adenine dinucleotide field effect transistor flow injection analysis amplification factor glucose oxidase glucose-6-phosphate dehydrogenase hepatitis B surface antigen human chorionic gonadotropin... 

Under these conditions the sensor response is directly proportional to analyte concentration. Further, if the term in brackets (called the enzyme loading factor by Carr and Bowers [24]) is greater than unity, this equation reduces to... 

Provided that external diffusion is not limiting, P depends linearly on S and the ratio of the substrate and product diffusion coefficients (/> and Dp), and nonlinearly on a square-root expression, the so-called Thiele modulus (the square of which is the enzyme loading factor, 4). 

Practically, the enzyme reaction can be considered first order when the concentration of the detected species is below mie-fifth of Km, i.e., 5o < 0.2Km, [9]. This case is rather typical for biosensors with high enzyme loading factor. 

Figure 4.3 Variation in the concentration // / of the detected product with the substrate concentration [S]o as a function cf the enzyme loading factor a.

The stability of enzyme sensors is thus related to the enzyme loading factor a of the active membrane. When the membrane contains more active enzyme, the biosensor is more stable and has a longer lifetime. We will see, however, that it is not always possible to satisfy this... 

Enzymatic hydrolysis is affected by numerous process factors including pH, temperature, reaction time, and enzyme loading. These factors often interact with one another. In the current study the main and interactive effects of four factors (reaction time, enzyme to... 

This study employed conventional diffusion-reaction theory, showing that with diffusion-limited reactions the internal effectiveness factor of a heterogeneous catalyst is inversely related to the Thiele modulus. Using a standard definition of the Thiele modulus [100], the observed reaction rate of an immobilized-enzyme reaction will vary with the square root of the immobilized-enzyme concentration in a diffusion-limited system. In this case, a plot of the reaction rate versus the enzyme loading in the catalyst formulation will be nonlinear. 

EC e.e. ELF EMEA EPC EPO Es Enzyme commission Enantiomeric excess Effluent load factor European medicines evaluation agency European Patent Convention European Patent Office Taft steric parameter... 

Theoretically, t is independent of the enzyme loading. As shown in Table 14, the calculated values of t have a maximum scattering factor of 5. If one takes account of uncontrollable changes in the membrane thickness resulting from sensor preparation, this is quite a good agreement. 

Ihble 14-10. Amplification factor and characteristic diffusion time in the lactate recycling system as a function of the enzyme loading. 

Enzyme immobilisation on mesoporous silica has also proved attractive for biocatalysis applications, particularly in nonaqueous solvents, since immobilisation of enzymes results in increased mechanical stability and potential for catalyst recyclingMany factors, such as relative size of nanopore/enzyme, nanopore volume, surface characteristics of support/enzyme influence enzyme loading and activity Enzymes... 

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