. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 100 HENRY T. YOST, JR., HOPE H. ROBSON AND I. M. SPIEGLEMAN II produced about as much inactivation as 4 minutes with Filter I; three hours with Filter II is equivalent to 10 minutes with Filter I. It seems that Filter II is only about %5 as effective as Filter I (about 6%}. Figure 2 presents the relation between the inactivation of cytochrome oxidase and the dosage of ultraviolet. The curve was obtained using Filter I. This curve is a composite and should be considered only as a rough indication of the course of inactivation
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 100 HENRY T. YOST, JR., HOPE H. ROBSON AND I. M. SPIEGLEMAN II produced about as much inactivation as 4 minutes with Filter I; three hours with Filter II is equivalent to 10 minutes with Filter I. It seems that Filter II is only about %5 as effective as Filter I (about 6%}. Figure 2 presents the relation between the inactivation of cytochrome oxidase and the dosage of ultraviolet. The curve was obtained using Filter I. This curve is a composite and should be considered only as a rough indication of the course of inactivation. All the points represent average values from several experiments. There is some variability expected in this case, since if one uses the same rat liver for all points on the curve, the controls are slowly losing activity with age, and if one uses different preparations for the different points, there is variation in the cytochrome oxidase concentration of the initial suspensions. However, it is clear that the initial inactivation of the enzyme is rapid, but the slope of the curve be- comes more gradual after 20 minutes, reaching a maximum inactivation at about c o U. 20 10 10 20 30 40 Dose: time in min. FIGURE 2. Inactivation of cytochrome oxidase by ultraviolet radiation. Radiation at high intensity; filter I; preparation diluted 1 in 5. Activity is expressed as per cent of the control activity. one hour. This curve is similar to the inactivation curves obtained with micro- organisms, and the shape is probably due to the gradual increase in protection against radiation by the inactivated enzyme. At the high intensity of radiation used in these experiments, it was not possible to determine the threshold value for the inactivation. Therefore the intensity was reduced by moving the flask away from the source. The data obtained with this lower intensity radiation are pre- sented in Figure 3. It is evident that there is a definite threshold value for the inactivation, and that th
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