Michaelis-Menton analysis

As an example, the data from Ketchum (37) for the rate of phosphate absorption as a function of both phosphate and nitrate concentration can be satisfactorily fit with a product of two Michaelis-Menton expressions. The resulting fit, obtained by a multiple nonlinear regression analysis, is shown in Figure 5. The Michaelis constants that result are 28.4 p.g NOa-N/liter and 30.3 pg P04-P/liter, with a saturated absorption rate of 15.1 X 10 8 pg P04-P/cell-hr. This approximation to the growth rate behavior as a function of more than one nutrient must be regarded as only a first approximation, however, since the complex interaction reported between the nutrients is neglected. 

Finally, we end the chapter with a discussion of nature s catalysts enzymes. In fact, we allude to enzymes throughout the chapter. The general manner in which enzymes catalyze reactions is still a matter of debate, and so we present several theories. Our examination of enzymes is in preparation for a few specific enzymatic examples given in Chapters 10 and 11 as highlights for organic reaction mechanisms. Enzymes also provide an excellent setting in which to discuss Michaelis-Menton kinetics, the most common kinetic scenario used for catalysis. We also return to our analysis of the power of changing the thermodynamic reference state to examine reactivity, and show the manner in which an enzyme becomes "perfect". 

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