Catalase inactivation

Figure 2. Warming-rate dependence of catalase inactivation in various solutions after seeding and quenching in liquid nitrogen. Mean and SE are shown for 4-6 samples in each case. Rates were controlled from —20, —30, and —50°C or lower for solutions containing phosphate only, KCl, and NaCl, respectively...

Figure 6. Cooling-rate dependence of catalase inactivation in lOmM neutral KHPO solutions containing various concentrations of NaCl. All solutions were seeded, cooled at stated rates to —50°C or lower, and then warmed at 0.5°C/ min from —50°C. Mean and SE are shown for four to six samples in each case...

Figure 9. Progression of catalase inactivation on storage at —40° in various...

Table V. Effect of Various Buffers on Catalase Inactivation...

In 1975, the U.S. Department of Agriculture (7) recommended that, for the majority of vegetables, catalase inactivation was not a satisfactory predictor of storage stability and that inactivation of peroxidase was necessary to minimize deterioration of quality during frozen storage. Use of peroxidase as the indicator is not without problems as it can recover its activity under certain conditions (8, 9). With the exception of asparagus, there is no evidence that peroxidase is directly associated with quality deterioration in most plant materials. 

Even under these conditions, the value of k should increase linearly with the donor concentration and no maximum value of k exists as it does for the simpler mechanism of equations (3) and (4). Experimentally, maximal values of k are often quoted in various papers, but they may be attributed to insufficient substrate concentration (the inequality A)Xo kiOo is violated), or to enzyme inactivation due to the excess peroxide concentration. For example, catalase inactivation can be caused by the formation of the inactive catalase complex II. In these cases it is desirable to use a lower value of substrate concentration and a smaller enzyme turnover number in order to avoid the inactivation. 

In another method, hydrogen peroxide can be added to the Hquid egg white after it has been heated at 52°C for a holding time of 1 minute (18) to inactivate the natural catalase and to allow the hydrogen peroxide to react against bacteria. Hoi ding time after addition of the hydrogen peroxide is 2.5 min... 

The multilayer shells can also provide a protective barrier for the loaded enzyme in environments where enzyme-degrading substrates such as proteases may be present [67]. Dissolved catalase was inactivated immediately by protease, losing its entire activity within 60 min in solution. For catalase loaded in BMS spheres, inactivation is slower, with an activity loss of about 20 % in 60 min. Notably, a negligible decrease in... 

Catalase and glutathione peroxidase provide two important cellular systems for eliminating H202. Catalase, a 56kDa cytosolic hemoprotein homotetramer that can act without a cofactor, although it may bind NAD(P)H, functions as a peroxidase to convert H202 to water. It can be irreversibly inactivated by oxidation and demonstrates decreased activity after ischemia-reperfusion. Catalase is more abundant in astrocytes than in neurons and in white matter than in gray matter, but it can be induced in neurons by neurotrophins. There is substantially less catalase activity in brain than in other tissues, such as liver. 

Compound III, like compound II, is an inactive form of catalase with respect to the normal catalatic cycle, and thus may contribute to the inactivation of the enzyme at high peroxide levels (42). 

The role of NADPH as protective donor 58, 59) seems to correlate well with the tendency of the different categories of catalases to form the inactive compoimd II. Only those classical catalases that are vulnerable to the latter inactivation step show NADP+ and NADPH binding. The scheme shown in Fig. 3B summarizes the minimal revisions of the 1958 scheme (Fig. 3A) needed to accommodate the newer findings. 

Erythrocytes also have systems that can inactivate ROS (superoxide dismutase, catalase, GSH). They are also able to repair damage caused by ROS. This requires products that are supplied by the erythrocytes maintenance metaboiism, which basically only involves anaerobic glycolysis (see p. 150) and the pentose phosphate pathway (PPP see p. 152). 

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