. Biophysical science. Biophysics. 18 : 1/ Enzymes: Kinetics of Oxidations 335 presence of an excess of hydrogen peroxide, an entirely different absorp- tion spectrum is developed. In contrast to the first complex, the second one appears red. It is enzymatically inactive. Both types of complexes are easier to study with either methyl hydrogen peroxide, CH3OOH, or ethyl hydrogen peroxide, C2H5OOH. Catalase reacts with these two alkyl peroxides to form both the green and the red complexes, but it does not decompose the alkyl peroxides. Spectra for the complexes with methyl hydrogen peroxide are
. Biophysical science. Biophysics. 18 : 1/ Enzymes: Kinetics of Oxidations 335 presence of an excess of hydrogen peroxide, an entirely different absorp- tion spectrum is developed. In contrast to the first complex, the second one appears red. It is enzymatically inactive. Both types of complexes are easier to study with either methyl hydrogen peroxide, CH3OOH, or ethyl hydrogen peroxide, C2H5OOH. Catalase reacts with these two alkyl peroxides to form both the green and the red complexes, but it does not decompose the alkyl peroxides. Spectra for the complexes with methyl hydrogen peroxide are shown in Figure 3. Catalase reactions are convenient to study spectrophotometrically for another reason. Besides the possibility for rapid observations afforded ^ <§• Reduced Oxidized 200. 600 Figure 2. Spectra of the oxidized and reduced forms of an algal cytochrome, Porphyra tenera, cytochrome 553. Spectra from solutions of crystalized enzyme. After S. Katoh, "Crystallization of an Algal Cytochrome," Nature 186: 138 (1960). by the spectral absorption changes of the enzyme, the peroxide concen- trations can also be observed by measuring the absorption in the ultra- violet region. The spectra of peroxides do not show sharp bands, but rather a curve which rises steadily as the wavelength is decreased from 300 m^ to less than 200 m/x. Because many proteins have a minimum in their absorption around 250-230 m/x, this wavelength band has been used to measure the peroxide concentration. Finally, in the peroxidatic reactions, it is often possible to observe the oxidation of AH2 to A in terms of spectrophotometry changes. Such studies have shown that the peroxidatic reaction can be repre- sented by the stoichiometric equations e — p x kx p E + S^E-S fca p a k, E-S + AH2- E + A + Products. 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
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