Ozone enzyme inhibition

Phenolic compounds naturally occurring in plants have induced many physiological responses that duplicate those reported for ozone and/or peroxyacetylnitrate (PAN). Chlorogenic acid is a competitive inhibitor of lAA-oxidase (35) and plant growth is adversely affected by increased concentrations of auxins (36). Concentrations of chlorogenic acid are increased in tobacco tissue exposed to ozone ( ) Phenols inhibit ATP synthesis (37), oxidative phosphorylation ( ) and SH enzyme activity (27) they increase respiration (38), reduce CO2 fixation (22), modify both membrane permeability (40) and oxidation rate of reduced NADH... 

Several reports of the effects of ozone in vivo are presented in Table XII. It is impossible to decide whether the effects of ozone are primary reactions or the result of a series of reactions initiated by ozone. All results can be rationalized as enzyme inhibition of one sort or another. Effects on membrane structure are harder to observe, and in one case it was reported that the malonaldehyde which would be expected on fatty acid ozonolysis was only observed after symptoms were apparent (74). Results of electron microscope examination showed that the first observable damage was in the stroma of the chloroplasts (70). One can easily argue that earlier damage could not be detected by microscopic techniques. However, recent reports that the chloroplast polyribosomes are much more susceptible to degradation by ozone are important observations which are consistent with the microscopy experiments (76). Chloroplast polysomes are also more susceptible to sulfhydryl reagents than are cytoplasmic polysomes (77). This evidence indicates that ozone itself, or a toxic product from primary oxidation, can pass through the cytoplasm and have its effect in the chloroplast. 

As discussed in detail by Dillard et al. and by Mittman et al. the possible relationship of lysosomal proteases to chronic lung disease has been inferred from the finding of an increased incidence of emphysema in subjects deficient in serum ai>antitrypsin factor, an -globulin that can inhibit lysosomal proteases. (No effect of ozone on serum aj-antitrypsin inhibitor was noted in rabbits chronically exposed to ozone. ) Thus, an ozone-induced increase in concentrations of such enzymes in the lung might produce excess proteolysis and result in eventual chronic lung disease. However, the available evidence is inadequate to support the belief that such a process occurs in humans intermittently exposed to ozone. Further studies of this potential hazard would be of value. 

Estimation of the Binding Site. Tryptophan-108 shows a specific reaction with iodine, distinguishing it from other tryptophan residues of lysoz3mie. When try-108 is selectively oxidized by iodine, lysozyme completely loses its activity. Nevertheless, the lysozyme still shows the ability to form an enzyme-substrate complex with CM-chitin. This observation contributes to the conclusion that try-62 is an essential binding site for a complex formation (13). All ozonized lysozymes formed strong complexes with CM-chitin and could only be eluted by 0.2N HA (Fig. 6). This further confirms that two tryptophan residues (108 and 111) are indispensible for the hydrolytic action of lysozyme, and that inactivation by ozone cannot be attributed to inhibition of substrate binding capability. 

When soybean leaves and pine needles were exposed to ozone, there was an initial decrease in the levels of soluble sugars followed by a subsequent increase. Ozone exposure also caused a decrease in the activity of the glycolytic pathway and the decrease in the activity was reflected in a lowered rate of nitrate reduction. Amino acids and protein also accumulated in soybean leaves following exposure. Ozone increased the activities of enzymes involved in phenol metabolism (phenylalanine ammonia lyase and polyphenoloxidase). There was also an increase in the levels of total phenols. Leachates from fescue leaves exposed to ozone inhibited nodulation. 

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