Whole-cell Michaelis-Menten

Figure 3. Schematic view of the substrate uptake rate versus concentration relationship as described by the whole-cell Michaelis-Menten kinetics. Q is the substrate uptake rate, <2max the biologically determined maximum uptake rate per biomass, c the substrate concentration, and Kj the whole-cell Michaelis constant, i.e. the concentration resulting in 2max/2 (mass of substrate per volume). At c

Because of its prominent appearance in the whole cell Michaelis-Menten equation, Kt is frequently mistaken as a measure of the substrate affinity. However, from equations (2) and (4), it becomes obvious that the activity versus concentration relationship is characterised by the two independent parameters, 2max, as a descriptor of the zero-order part at high substrate concentration, and a°A, as a descriptor of the slope of the first-order part of the curve. In his much-cited review paper, Button [9] has listed the specific affinities of various organisms for a range of carbon sources and other elements. Reported variations for the same substrates extend over up to four orders of magnitude. Table 1 updates... 

Bosma et al. [1] have proposed including the details of extracellular substrate transport in the calculation of whole-cell Michaelis-Menten kinetics. For the situation of a quasi-steady-state (i.e. when the transport flux and the rate of degradation of the substrate are equal) the consumption of substrate by a microorganism is represented as a function of the distant, and effectively unavailable, substrate concentration ca ... 

When whole cell containing plural enzymes with opposite selectivities and different (Michaelis-Menten constant) values are used, problems of low selectivities occur. If the substrate concentration is decreased, one of the enzymes with low Kra value catalyzes the reaction so that the selectivity can be improved. 

Table 3. Representative affinity constants for the binding of metal to transport sites or whole cells/organisms. Ionic strengths and pH values are given for the conditional constants. In the column Comments , information on the method of determination (Km = Michaelis-Menten constant WC = whole-cell titrations) the type of constant (CC = conditional constant IC = intrinsic constant) and special conditions (Cl = competitive inhibitors NICA = nonideal competitive adsorption) are given...

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