INITIAL RATE ENZYME DATA REPORTING

The initial rate assumption is one of the most powerful and widely used assumptions in the kinetic characterization of enzyme action. The proper choice of reaction conditions that satisfy the initial rate assumption is itself a challenge, but once conditions are established for initial rate measurements, the kinetic treatment of an enzyme s rate behavior becomes much more tractablek In reporting initial rate data, investigators would be well advised to provide the following information ... 

Data of release rates for seven enzymes from baker s yeast with a high-pressure homogenizer revealed that differences in release rates agreed with reported locations in the cell but are not sufficient to fractionate the enzymes release rates did not seem to depend much on operating pressure, temperature, or initial cell concentration (Follows, 1971). Both the dependence of release rates on the location within the cell and the description of release by a first-order law has been confirmed in both yeast and E. coli with several disruption techniques such as sonica-tion, high-pressure homogenization, and hydrodynamic cavitation (Balasundaram, 2001). 

B. Ranby "I have not seen these data reported before. In the hydrolysis by acid we know that it is an initial phase which takes something like 10% away from the cellulose very quickly and then the rate of reaction is much slower. Therefore, the reaction is not first order throughout. Referring to Dr. Selby s report apparently the enzyme is... 

A Lineweaver-Burk plot ( ) indicates that with D-glucose as the substrate, the enzyme obeys Michaelis-Menten kinetics with a Km value of 3.2 + 0.08 mM and a Vmax of 126.0 + 0.02 micromol/mg protein/min (Figure 11). Similar results were obtained by the direct linear plot (88), Hanes and Woolf ( ) or Eadie-Hofstee plots (90). All the kinetic data reported here and subsequently, were based on the initial rates of hydrogen peroxide formation... 

The kinetic data below were reported for an enzyme catalyzed reaction of the type E + S ES E + P. Since the data pertain to initial reaction rates, the reverse reaction may be neglected. Use a graphical method to determine the Michaelis constant and Fmax for this system at the enzyme concentration employed. 

In both cases the initial substrate concentration was 0.14kmol/m. In cases (a) and (b) the Michaelis constants (K ) are reported to be 1.15 X 10" and 1.5 X 10" kmol/m, respectively. The rate constant is equal to 1.25 pmol/(m -s-unitof enzyme) in both cases. If the data are not consistent, provide plausible explanations for the discrepancy. 

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