Evidence for tissue-specific electromorphs of Cu/Zn SOD unrelated to genetic control

cDNA cloning, high-level expression, purification, and characterization of an avian Cu,Zn superoxide dismutase from Peking duck

As a special species of avian, Peking duck is often used as a model for exploring effective factors against cardio-cerebrovascular diseases, and therefore investigations of antioxidant enzymes including superoxide dismutase are intriguing. By using 3(')-RACE with a gene-specific primer, a cDNA encoding duck Cu,Zn SOD was amplified from the total RNA extracted from Peking duck liver. Three free cysteine residues are found in the deduced amino acid sequence of duck SOD, among which Cys153 at the carbonyl-terminal is a distinctive feature. Production with a high yield of recombinant duck Cu,Zn SOD was achieved in Escherichia coli after the reconstituted expression vector pET-3a-dSOD was transformed into the bacterial strain BL21(DE3)pLysS. After two steps of anion exchange chromatography, a great quantity of the purified enzyme (100mg/L fermented culture) with an enzymatic activity comparable to that of native duck and bovine SOD was finally obtained. Duck SOD is a homodimer with 153 residues for each subunit. The molecular mass of the recombinant enzyme is 15,540.0Da measured by mass spectrum, which well coincides with the estimated size of the sequence but significantly differs from that of the native counterpart. Five charge isomers were observed on isoelectricfocusing (IEF). The most interesting observation is that the thermal stability of duck SOD is much lower than that of the bovine enzyme as revealed by irreversible heat inactivation at 70 degrees C. These properties are discussed in relation to the distinctive free Cys residues in duck Cu,Zn SOD.

Purification of Cu, Zn-superoxide dismutase isoenzymes from fish liver: appearance of new isoforms as a consequence of pollution

Liver cell-free extracts of fish (Mugil sp.) from polluted environments show new Cu,Zn-SOD isoenzymes when analyzed by polyacrylamide gel electrophoresis or isoelectrofocusing followed by in situ staining for SOD activity. The most active isoenzymes, with pI 6.1 and 5.1, were present both in control and problem samples while the isoenzymes of intermediate pI value showed significant differences. Fish from control areas showed three intermediate isoenzymes with pI 5.7, 5.5 and 5.4 (the last one quite faint) while polluted animals showed three bands of pI 5.9, 5.45 and 5.35, this last very intense. To further characterize their utility as biomarkers, Cu,Zn-SOD isoenzymes from polluted fish livers were purified to homogeneity. Five superoxide dismutase peaks were purified, named thereafter I (pI 6.1) to V (pI 5.1) respectively. Isoenzymes I and V displayed the highest specific activity. Upon incubation with moderate H2O2 concentrations, pure isoenzyme I yielded more acidic bands with pI 5.5, 5.45 and 5.35, this last being predominant. The pure isoenzyme V generated only a new band of pI 5.0. Concomitant with oxidation, the activity of peaks I and V was lost in a H2O2 concentration-dependent manner. The pattern of the new acidic bands generated upon the oxidixing treatment of isoenzyme I closely resembles that observed in crude extracts from polluted animals.

Multiple isoelectric variants of copper, zinc-superoxide dismutase from rat liver

Isoelectric variants of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) have been reported to exist in various organs including rat liver. To elucidate the biochemical characteristics of the variants, rat liver Cu,Zn-SOD was purified and isolated into eight variants, i.e., pI 5.15, 4.88, 4.80, 4.75, 4.70, 4.65, 4.60, and 4.50. The pI 4.88 variant had the highest specific activity (4245 U/mg protein) and the highest yield (45% of original activity). The descending order of specific activity for the other variants was pI 4.80, 4.75, 5.15, 4.70, 4.65, 4.60, and 4.50. The specific activity correlated well with metal content. The specific activity for most variants was 5-9 times greater when determined at pH 10.0 than at pH 7.8. However, three preparations of pI 4.80 and 4.70 variants had 13.9-16.3 times greater specific activity at pH 10.0 versus 7.8, while one of the pI 4.60 variants was only 3.5 times greater. The rate of Coomasie brilliant blue G-250 binding was lowest with pI 4.88 followed by pIs 4.80 and 4.75. To evaluate the mechanisms which might produce these variants, the pI 4.88 variant was incubated with xanthine-xanthine oxidase or a mixture of rat liver microsome, NADPH, and sodium azide, and a shift to variants pI 4.80 and pI 4.75 was found. The shift was greatly inhibited by the presence of mannitol or by the omitting of azide, respectively. The existence of these variants was also confirmed by other methods: (i) direct application of rat liver 105,000g supernatant to an isoelectric focusing, and (ii) extraction of SOD from acetone powder prepared from rat liver homogenate. Results indicate that several variants most likely arise in tissue as a result of activated oxygen radical modification of variant pI 4.88.

Aspects of the structure, function, and applications of superoxide dismutase

The current status of superoxide dismutase (SOD) is that it is an enzyme with diverse ramifications. This review attempts an understanding of SOD as a structural, functional, and biological entity. Accordingly, the review is in three parts. The first part discusses SOD in terms of protein structure, proceeding from primary to secondary and three-dimensional structure for the three forms of SOD: copper/zinc SOD, manganese SOD, and iron SOD. This is the order of structural knowledge of the enzyme. Iron SOD is an enzyme of prokaryotes and some higher plants. Manganese SOD is an enzyme of prokaryotes and eukaryotes. Copper/zinc SOD is an enzyme of eukaryotes and certain prokaryotes. The evolutionary relationships of the three forms of SOD, the status of the copper/zinc SOD gene in prokaryotes, and the cloning and sequencing of SOD genes are discussed. The second part of the review deals with the catalytic mechanism of SOD in the three forms of the enzyme. Structural and mechanistic conclusions from various spectroscopic studies are critically considered. A detailed picture is given of the active site of copper/zinc SOD. The third part is a review of SOD in the general context of oxygen toxicity. After consideration of the question of superoxide toxicity and superoxide pathology, several areas in which SOD has been investigated or used as a tool in a biochemical, pharmacological, or clinical context are discussed, including population genetics; trisomy 21; development and senescence; the nutritional copper, zinc, and manganese status; hemolysis and anemia; oxygen toxicity in the lung and nervous system; inflammation, autoimmune disease and chromosome breakage, ischemia and degenerative changes; radiation damage; and malignancy. A comprehensive picture is given of measurements of SOD activity in disease states, and the question of superoxide-related disease is considered at several points.

Aging of the erythrocyte--XVII. Changes in the properties of superoxide dismutase

1. An increase in the sensitivity of superoxide dismutase (SOD) to the action of diethyldithio-carbamate and cyanide was observed in red cell fractions of greater age. 2. It suggests that SOD inactivation during erythrocyte aging is not an "all or none" process but involves transition(s) between enzyme forms of different properties. 3. An increase in the ratio of less mobile to the more mobile SOD bands was observed by polyacrylamide-gel-electrophoresis in older erythrocytes.