. Biophysics: concepts and mechanisms. Biophysics. ON CHEMICAL REACTION RATES; ENZYMES 205 that obtained by measuring rates at various concentrations of substrate and enzyme. The "catalyst law" (for enzymes, the Michaelis-Menten expression) rear- ranges to [S\ W£]„ - K eq from which it is seen that the slope of a plot ofv/[S]0 vs v gives K (= 1/A"m) directly as the negative of the slope. Figure 8-7 is such a plot for the hy- drolysis of a particular dipeptide for which the stomach enzyme, pepsin, is a specific catalyst. The value of Km obtained is moles liter-1. This resu
. Biophysics: concepts and mechanisms. Biophysics. ON CHEMICAL REACTION RATES; ENZYMES 205 that obtained by measuring rates at various concentrations of substrate and enzyme. The "catalyst law" (for enzymes, the Michaelis-Menten expression) rear- ranges to [S\ W£]„ - K eq from which it is seen that the slope of a plot ofv/[S]0 vs v gives K (= 1/A"m) directly as the negative of the slope. Figure 8-7 is such a plot for the hy- drolysis of a particular dipeptide for which the stomach enzyme, pepsin, is a specific catalyst. The value of Km obtained is moles liter-1. This result is typical. The inverse, the value of K at 25°, will usually be found to be between 100 and 600 liters/mole, which means that the substrate must be in excess 100- to 600-fold over the enzyme if the catalyst is to be more than 90 per cent complexed (, "worked hard") at all times. There are cases (certain chymotrypsin-catalyzed reactions, for example) in which the binding of the complex is much stronger. By contrast, the myosin-adenosine triphosphate complex, formed during muscle contraction is relatively a very weak The value of Km is numerically equal to that value of the substrate concentration at which one-half the enzyme molecules are tied up as complexes. Electrical attractions and repulsions as well as the geometry of the molecules E and S determine the extent of Keq = 700. Figure 8-7. Determination of the Binding Constant of the Intermediate Complex in a Catalyzed Reaction (pepsin-catalyzed hydrolysis of carbobenzoxy-glutamyl-tyrosine ethyl ester, a dipeptide). Values plotted are those of initial rates found experimentally for six different initial concentrations of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Casey, Edmund Jeremiah, 1924-. New York, Rein
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