Superoxide dismutase: an evolutionary puzzle

We have obtained the complete amino acid sequence of copper/zinc-containing superoxide dismutase (SOD, superoxide:superoxide oxidoreductase, EC 1.15.1.1) from Drosophila melanogaster. The sequence of this enzyme is also known for man, horse, cow, and the yeast Saccharomyces cerevisiae. The rate of evolution of this enzyme is far from constant. The number of amino acid substitutions per 100 residues per 100 million years is 30.9 when the three mammals are compared to each other, 10.6 when Drosophila is compared to the three mammals, and 5.8 when the yeast is compared to the four animals. The first value represents one of the fastest evolutionary rates for any protein, the second is similar to the globin rate, and the third is similar to some cytochromes and other slowly evolving proteins. Hence, SOD is not an acceptable evolutionary clock. Another peculiarity of this enzyme is that a two-amino-acid deletion must have occurred independently in the lineages going to the cow and to Drosophila. We conclude that using the primary structure of a single gene or protein to time evolutionary events or to reconstruct phylogenetic relationships is potentially fraught with error.

Primary seminoma of the mediastinum. Cancer Control Agency of British Columbia experience

Six patients with primary seminoma of the mediastinum were treated at the Cancer Control Agency of British Columbia during the period from 1970 to 1982. Primary treatment used was external beam radiotherapy. Only one patient received both radiotherapy and chemotherapy. Tumor dose ranged from 3000 cGy in 16 daily fractions in 3 weeks to 3500 cGy in 20 daily fractions in 4 weeks using parallel opposed fields on megavoltage machines. Two patients received additional small-volume boost to the superior mediastinum, delivering 500 cGy and 1000 cGy, respectively. All patients had complete resolution of the mediastinal mass after treatment and are alive and free of disease. One patient developed a metastasis to the fifth lumbar vertebra 1 year after treatment. This metastatic lesion was treated with radiotherapy and the patient is alive and free of clinical disease. Mediastinal seminoma is radiosensitive and radiocurable.

Superoxide dismutase in Drosophila melanogaster. Mutation site difference between two electromorphs

Two electrophoretically distinguishable variants of superoxide dismutase (SOD) are common in natural populations of Drosophila melanogaster. We have earlier comparatively characterized these two electromorphs, SODF and SODS. By peptide mapping in high-performance liquid chromatography (HPLC), we now show that the difference between the two electromorphs is due to the replacement of Asn-96 (SODF) by Lys-96 (SODS). It is far from clear how this replacement causes the biochemical differences (in thermostability, specific activity, and others) observed between these two forms of the enzyme.

Interactions of heme proteins with hydrogen peroxide: protein crosslinking and covalent binding of benzo[a]pyrene and 17 beta-estradiol

This work reveals two biochemical effects of hydrogen peroxide treatment on hemoglobin, myoglobin, and cytochrome c. First, these heme proteins rapidly formed covalently crosslinked dimers and polymers detectable by detergent gel electrophoresis. Second, when treated in the presence of radioactive benzo[a]pyrene or 17 beta-estradiol, the heme proteins became covalently labeled. Nonheme proteins exhibited both cross-linking and radioactive labeling upon peroxide treatment in the presence but not the absence of heme protein or free hemin. Benzoyl peroxide or glucose and glucose oxidase effectively replaced direct addition of hydrogen peroxide. These results indicate that adventitious peroxidase activity expressed by oxygen carrying and electron transport proteins yields active oxygen species that can damage these heme proteins and nearby macromolecules, a possible biochemical mechanism for the lethal and other deleterious intracellular effects of peroxide.

Superoxide dismutase in Drosophila melanogaster: biochemical and structural characterization of allozyme variants

Superoxide dismutase (SOD; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is known to be polymorphic in many organisms; in Drosophila, the degree of polymorphism has a wide range of variation from locality to locality within a given species. We have thoroughly purified from D. melanogaster the two common electromorphs, SODS and SODF. These differ in properties such as isoelectric point, specific activity, rate constant, thermostability, and amino acid composition. The specific activity is three times greater in SODS than in SODF, but the latter is more thermostable. In strains from California, SODS differs from SODF by at least one amino acid substitution: lysine in SODS is replaced by either aspartic acid or asparagine in SODF. This difference is consistent with the electrophoretic mobility and isoelectric points of the two electromorphs. In strains from Africa, SODS and SODF differ by two amino acid substitutions (histidine and proline in SODS vs. serine and either glutamic acid or glutamine in SODF) in addition to the one distinguishing the California strains. Thus the SODF electromorphs from California and from Tunisia, in spite of their identical electrophoretic mobility, differ by at least two amino acid substitutions.

Purification and properties of superoxide dismutase from Drosophila melanogaster

The major superoxide dismutase ("slow" electromorph) of the fruit fly, Drosophila melanogaster, has been purified to homogeneity. This enzyme contains 2 Cu2+ and 2 Zn2+/molecule. The ultraviolet absorption spectrum indicates a lack of tryptophan. This enzyme has a molecular weight of 32,000 and is composed of two subunits of equal size, which are joined by noncovalent interactions. Cyanide at 1 and 3 mM inhibits the activity of superoxide dismutase 92 and 100%, but 5 and 10 mM azide caused 15 and 30% inhibition. The isoelectric point, assessed by isoelectric focusing, is 5.3. Amino acid analyses, as well as the spectral and catalytic properties, are reported. The D. melanogaster superoxide dismutase does not cross-react with antibodies to bovine erythrocyte Cu-Zn-containing superoxide dismutase nor to Escherichia coli manganese- and iron-containing superoxide dismutases.

Inactivation of phosphorylase b by potassium ferrate. Identification of a tyrosine residue involved in the binding of adenosine 5'-monophosphate

The site of reaction of potassium ferrate (K2FeO4) with rabbit muscle phosphorylase b has been further characterized in an extension of previously published studies (Lee, Y. M., and Benisek, W. F. (1976) J. Biol, Chem. 251, 1553-1560) reporting inactivation of the enzyme by this reagent. The tryptic peptide composed of residues 70 to 80 of the enzyme's polypeptide chain was shown to contain a tyrosine residue which is chemically modified by ferrate and which is protected by 5'-AMP. The sequence of this peptide obtained from both untreated and ferrate-treated phosphorylase b was determined, and the results showed that tyrosine-75 was the residue with which ferrate reacts.

Inactivation of phosphorylase b by potassium ferrate, a new reactive analogue of the phosphate group

Rabbit muscle phosphorylase b reacts with the phosphate-like reagent potassium ferrate, K2FeO4, a potent oxidizing agent. The reaction results in inactivation of the enzyme and abolition of the ability of the enzyme to bind 5'-AMP. Activating and nonactivating nucleotides which bind at the 5'-AMP binding site such as 5'-AMP, 2'-AMP, 3'-AMP, and 5'-IMP substantially protect the enzyme from inactivation by ferrate. One to two residues of tyrosine and approximately 1 residue of cysteine are modified by ferrate under the conditions employed. Tyrosine is protected by 5-AMP, whereas cysteine is not. The tyrosine modification is suggested as the inactivating chemical reaction. The location of the inactivating reaction is suggested to be in or near the 5'-AMP binding site. The structural and chemical properties of ferrate ion are discussed and compared to those of phosphate. Ferrate ion may be a reagent useful for phosphate group binding site-directed modification of proteins.