Structural and Functional Changes in Catalase Induced by Near‐UV Radiation

Abstract

Part one of this study shows that exposure of purified beef liver catalase in buffered solutions to BL lamps that provide a mixture of 99% UVA and 1% UVB (to be labeled UVA) alters its chemistry and enzymatic activity. Thus, its spectral absorbance lost detail, it aggregated and exhibited a lower isoelectric point and its enzymatic activity was substantially reduced. These photochemically induced changes were increased by irradiation in phosphate buffer or in physiological medium (minimal essential medium) containing riboflavin and tryptophan. Neither alpha-tocopherol nor deferoxamine were protective against these UVA-induced changes in pure catalase. We further investigated the effect of UVA radiation on the activity of catalase in cultured lens epithelial cells and the protective effects of antioxidants. Cultured lens epithelial cells of rabbits and squirrels were exposed to near-UV radiation with representation in the UVA region of 99% and 1% UVB. Catalase assays were done on homogenate supernatants of cells kept dark or UV exposed. In some instances, cells were cultured in medium containing alpha-tocopherol or deferoxamine prior to UV radiation. Comparisons were made between UV-exposed lens cell catalase activity when exposure was done with or without the antioxidants. The UVA radiation was strongly inhibitory to both rabbit and squirrel lens epithelial cell catalase activities. The range of fluxes of near UV radiation was compatible with that which could reach the lens from the sunlit environment. Catalase inactivation was lessened in cells preincubated with alpha-tocopherol and deferoxamine. This suggests that both singlet oxygen and hydroxyl radical formation may be involved in near-UV damage to lens epithelial cell catalase. Such inhibition of catalase by near-UV would enhance H2O2 toxicity and stimulate SH oxidation so as to damage the lens.

Effects of N-acetylcysteine amide (NACA), a thiol antioxidant on radiation-induced cytotoxicity in Chinese hamster ovary cells

“…Catalase is one such enzyme found in peroxisomes that catalyzes the removal of hydrogen peroxide. According to our studies, radiation significantly decreased the activity of catalase, possibly due to oxidation of sulfhydryl groups of the enzyme active sites, or due to other structural and functional changes induced in the enzyme by ionizing radiation (Zigman et al, 1996). Both NAC and NACA were capable of returning catalase activity to control levels.…”

UVA Light In vivo Reaches the Nucleus of the Guinea Pig Lens and Produces Deleterious, Oxidative Effects

“…4). Catalase is highly susceptible to UVA-induced inhibition (Kramer and Ames, 1987;Zigman et al, 1996;Zigman et al, 2000), and because of its tightly bound heme and NADPH groups, it has been referred to as an endogenous cellular photosensitizer for UVA radiation (Kramer and Ames, 1987). Apparently, the remaining 40 % activity of catalase in the lenses of UVA-exposed animals was suf®cient to protect the lens epithelial cells against damage, since no morphological effects were observed in the anterior region of the lenses (Fig.…”

“…An investigation conducted with Chinese hamster ®broblasts (Banrud et al, 1999) found that while biologically-relevant uences of UVA were able to disintegrate actin ®laments in the cells, even lethal¯uences of UVB light had no effect on the proteins. Studies with cultured lenses have also indicated distinct damaging effects of UVA light on cytoskeletal proteins (Rafferty et al, 1993;Zigman et al, 1996;Weinreb et al, 2001); however, these studies investigated only damage to proteins present in the lens epithelium and cortex. The¯uences of UVA light used in the cultured lens work were at least 5±10 times higher than ours, which may be why the previous investigators were able to induce UVA damage in the epithelium and cortex, whereas we could not.…”

UVA Irradiation of Dysplastic Keratinocytes: Oxidative Damage versus Antioxidant Defense

“…It is commonly accepted that catalase photoinactivation occurs through an oxygen-dependent photooxidation of the heme groups that involve ROS [49–51]. In addition, UVA-mediated oxidative modification of the catalase apoprotein, leading to structural alterations and catalytic deactivation, were previously shown [52,53]. The initial decrease of the activity noted by us may be considered as a direct effect of UVA causing catalase photoinactivation, while the restoring increase registered after a 24 h post-irradiation culture of the UVA-exposed cells may be considered a protective response in the attempt to re-establish a basal level of catalase activity (Figure 6).…”