Substrate consumption

Where yield coefficients are constant for a particular cell cultivation system, knowledge of how one variable changes can be used to determine changes in the other. Such stoichiometric relationships can be useful in monitoring fermentations. For example, some product concentrations, such as CO2 leaving an aerobic bioreactor, are often the most convenient to measure in practice and give information on substrate consumption rates, biomass formation rates and product formation rates. 

The relationships between spedfic rate of substrate consumption and dilution rate and between yield coeffidents and dilution rates are shown in Figure 32. 

Maintenance energy requirements can be defined in terms of rate of substrate consumption per unit of biomass for maintenance this is known as the maintenance coefficient (m). 

With glucose as substrate, substrate consumption is fast causing rapid growth and a... 

It was found that the substrate consumption rate followed first-order kinetics with respect to substrate concentration.21,22 The expression of substrate consumption with time is written in a first-order differential equation ... 

Finally, at steady-state condition, as has been stated above (5.6.1.3), the rate of substrate consumption is equal to the biomass generation, with the assumption of zero death rate ... 

To answer these questions, at first mass balance is required to determine conversion and how much air to supply into the fermentation broth. The substrate consumption or production rates must be set as a start. To demonstrate suitable answers to the above statements, we may approach the questions by reviewing a few biological processes and illustrating all the assumptions and process conditions. 

Substrate Consumption. Consumption of substrates and generation of products can be described using empirical yield coefficients. Yields are usually based on the amount of limiting substrate that has been consumed. Thus, Ypjs denotes the mass of product produced per mass of substrate consumed, and Yxts denotes... 

Equation (12.15) governs substrate consumption. For a batch reactor with all the substrate charged initially,... 

The effect of a particular cultivation environment on a system can be evaluated in terms of biomass (fresh/dry weight, cell number), secondary metabolite production [51,75,89,102,103,106,107] or substrate consumption (e.g. carbon source [57] or oxygen [53,108]). Using the Evan s Blue method to identify non-viable cells. Ho et al. [108] used viable cell density measurements to determine variations in specific growth rate attributable to hydrodynamic stress. 

Cathanthus roseus Nicotiana tabacum Cinchona robusta Tabernaemontana divaricata 3-1 STR (2 1 wv) D 4.5 cm batch and chemostat N 2.5 -16.7 s Q 0.33 wm t < 30 d biomass production total organic carbon extracellular protein membrane integrity substrate consumption [107]... 

Fathepure BZ, SA Boyd (1988) Dependence of tetrachloroethylene dechlorination on methanogenic substrate consumption by Methanosarcina sp. strain DCM. Appl Environ Microbiol 54 2976-2980. 

Therefore if the carbon substrate is present at sufficiently high concentration anywhere in the rhizosphere (i.e., p p, ax), the microbial biomass will increase exponentially. Most models have considered the microbes to be immobile and so Eq. (33) can be solved independently for each position in the rhizosphere provided the substrate concentration is known. This, in turn, is simulated by treating substrate-carbon as the diffusing solute in Eq. (32). The substrate consumption by microorganisms is considered as a sink term in the diffusion equation, Eq. (8). 

Add a calculation of the operating parameters substrate consumption rate to micro-organisms ratio (Load), solids residence time (0m) and sludge age ((),) to the program. Experiment with variations in the values of these parameters under various conditions of flow and feed concentration to test their value as process control parameters. 

In the no substrate consumption zone, one passes upon increasing Xe (i.e., increasing the rate constant and/or decreasing the scan rate) from a... 

When Xe/y —> 0, catalysis vanishes. In the converse situation, where Xe/y oo, an interesting extreme behavior is observed. Substrate consumption is so rapid that substrate diffusion from the bulk of the solution to the electrode substrate becomes rate limiting. The cyclic voltammetric response... 

Although the general case may readily be resolved as shown in Section 6.5.1, two limiting situations are of particular practical interest.9 One is when the system obeys pure kinetic conditions (Section 2.2.6), that is, when the diffusion of the cosubsrate and its involvement in a fast enzymatic reaction mutually compensate. Under these conditions, the current responses are governed by the kinetics of the enzymatic reaction. If at the same time, substrate consumption is moderate enough for its concentration to be considered as constant, the current responses are plateau-shaped and obey the following equation (see Section 6.5.1) ... 

The characteristics of these S-shaped waves obtained under enzyme steady-state conditions and no substrate consumption are exactly the same in RDEV and in cyclic voltammetry. 

To give rise to oscillatory behavior instead of a biochemical explosion, selfamplification must, however, be coupled to a limiting process. Such a limiting process can be viewed as a form of negative feedback because it occurs as a consequence of the positive feedback that precedes it. Thus, in the case of glycolytic oscillations, the activation of phosphofructokinase by a reaction product is followed by a counteracting fall in the rate of the enzymatic reaction, due to the enhanced substrate consumption associated with enzyme activation. In Ca + pulsatile signaling, the explosive rise in cytosolic Ca + due... 

A further advantage, as described by Thomas et al. [19], is the possibility of protein identification that follows the functional characterization of the enzyme. The activity of an enzyme is initially determined by following the substrate consumption and product formation in the first assay (Fig. 8.10). Since no matrix components are present in the sample spot, the immobilized enzyme is then directly... 

Fig. 8.10 Sequential functional characterization and structural identification of an enzyme. Initially, information about the activity is obtained by assessing substrate consumption and product formation. Afterwards, the enzyme is digested on the plate, and the formed peptide fragments (F1-F4) are determined by means of mass spectrometry.

The relationship between reaction velocity and enzyme concentration (in the absence of self-association of the enzyme) should also be adjusted such that reaction rate is linearly related to catalyst concentration, [Etotai]- Initial rates typically fail to obtain if [Etotai] = 0-01 [Ajmitiai where [Ajinitiai is the initial substrate concentration. As a general rule, the substrate concentration will not have changed more than 5-10% of its value over the initial rate phase of the reaction. This rule-of-thumb applies only to thermodynamically favorable reactions, and investigators are well advised to limit substrate consumption to well below 5%. 

A mechanism in which reductive activation of dioxygen precedes the C—H bond cleavage cannot explain such a tight coupling of oxygen and substrate consumption. (From Crespo et ah, 2006)... 

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