Characterization of glutathione peroxidase in frog retina

Effect of muscle and post-mortem rate of pH and temperature fall on antioxidant enzyme activities in beef

The aim of this study was to investigate the effect of muscle, inner and outer Musculus biceps femoris (IBF and OBF respectively) and Musculus longissimus dorsi (LD), on the post-mortem rate of pH and temperature fall, and the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) during simulated retail display. At day 0 of display (2 days post-mortem), the CAT and GSH-Px activities were lower in IBF than in OBF and LD (P<0.001), and the SOD activity was lower in OBF compared to IBF and LD (P<0.001). At day 10 of display, SOD and CAT activities had decreased in all three muscles compared to day 0 (P<0.001), whereas the GSH-Px activity did increase with time of display. Across muscles, there were significant relationships between temperature fall, colour, lipid and colour stability and antioxidant enzyme activities.

Purification of phospholipid hydroperoxide glutathione peroxidase from bovine retina

A low molecular size peroxidase with a high affinity for phospholipid hydroperoxide was purified from bovine retina by sequential extraction with low and high ionic strength buffer, followed by ammonium sulfate fractionation, chromatography on an ultraspherogel column and Protein PAK-SP column. The purified enzyme has a low Km (0.011 mmol/L) for phospholipid hydroperoxide, and a high Km (1.37 mmol/L) for glutathione. Glutathione oxidation was competitively inhibited by vitamin E, Ki = 0.019 mmol/L. The retinal PHGPX is different from the PHGPX purified by others from heart and liver in molecular size. The molecular size estimated by gel filtration chromatography is below 6 kDa.

Lipid peroxidation and antioxidant enzymatic systems in rat retina as a function of age

In the present study, we have assayed the enzymatic activity of Cu,Zn-SOD, Mn-SOD, GSH-Px, GSH-Red, Cat, and G6PD in rat retina as a function of age. Conjugated diene levels and MDA formation were also determined. The conjugated diene levels in rat retina were found to increase significantly with age, accompanied by a marked decrease in GSH-Px and Cat activities. No age-related change in MDA levels and in GSH-Red and G6PD activity was found, whereas a significant increase in SOD activity was observed between 1 and 4 months. Decreased GSH-Px and Cat activity is related to increased lipid peroxidation with age.

Glutathione-dependent enzymes in intact rod outer segments

We have compared the specific activities of glutathione-dependent enzymes in rod outer segments (ROS) and in whole retina of rabbits and rats, using three different assays. In the first, glutathione peroxidase (GSH-Px) activity was measured as the combined activities of the Se-dependent and Se-independent forms using cumene hydroxide as a substrate. In the second, Se-dependent GSH-Px alone was measured using hydrogen peroxide (H2O2) as a substrate. In the third, the combined activities of several enzymes, collectively known as GSH-S-transferase, were measured. The latter includes the activity of the Se-independent GSH-Px. GSH-Px activity (Se-dependent and Se-independent combined) in ROS of rat and rabbit were found to be 47.7 +/- 8.2 and 72.9 +/- 11.9 nmol of GSH oxidized min-1 mg-1 soluble protein, respectively. From whole retina, values were 67.3 +/- 6.0 and 128.8 +/- 12.3, respectively. Se-dependent GSH-Px specific activities from the above tissues were 43.5 +/- 2.9 (rat ROS). 70.6 +/- 11.3 (rabbit ROS), 30.6 +/- 9.6 (rat whole retina), and 113.2 +/- 12.2 (rabbit whole retina). GSH-S-transferase activity was negligible in rabbit ROS, whereas, in rat ROS, it was 40.4 +/- 8.0, expressed as nmol of S-2,4-dinitrophenylglutathione produced min-1 mg-1 soluble protein. In contrast, the GSH-S-transferase specific activity in whole rabbit retinas was about eight times that found in the rat retina (101.5 +/- 12.3 for rat retina and 885.3 +/- 60.0 for rabbit retina). These results demonstrate that ROS contain glutathione enzymes which are important in protecting membranes from oxidative stresses by reducing hydrogen peroxide and lipid hydroperoxides at the site of their formation.

Effect of hyperoxia acclimation on catalase and glutathione peroxidase activities and in vivo peroxidation products in various tissues of the frog Rana ridibunda perezi

Among vertebrates, adult amphibians are known to be especially tolerant to exposure to high environmental oxygen tensions. To clarify the basis for this high O2 tolerance, adult Rana ridibunda perezi frogs were acclimated for 15 days to water-air phases with either 149 mm Hg O2 (normoxia) or 710 mm Hg O2 (hyperoxia). At the end of the acclimation, various morphometric and biochemical parameters related to oxidative stress were measured in seven organs and tissues. Hyperoxia acclimation did not change either the total weight of the animals or the total and relative wet weights of the organs studied, except for the brain, which showed weight increases in the hyperoxic group. In vivo tissue peroxidation increased in the kidney; decreased in the skeletal muscle and skin; and did not change in the liver, lung, brain, and heart after hyperoxic exposures. Whereas liver, lung, and skin showed glutathione peroxidase (GSH-Px) activities with both cumene hydroperoxide (cumene-OOH) and H2O2 as substrates, skeletal muscle only showed H2O2 GSH-Px activity. Hyperoxia acclimation did not change either catalase (CAT) or GSH-Px activities in any organ, except for the liver in which CAT activity was induced by hyperoxia. Thus hyperoxia tolerance in this species does not need the induction of H2O2-detoxifying enzymes in the majority of the organs. It is suggested that the high O2 tolerance of this amphibian species is related to its comparatively high constitutive GSH-Px activities.