Formation and photolability of low-spin ferrous cytochrome c peroxidase at alkaline pH.

The ferrous form of native cytochrome c peroxidase (CCP) is known to undergo a reversible transition when titrated over the pH range of 7.00-9.70. This transition produces a conversion from a pentacoordinate high-spin to a hexacoordinate low-spin heme active site and is clearly apparent in the heme optical absorption spectra. Here, we report the characterization of this transition and its effect upon the local heme environment using various optical spectroscopies. The formation of hexacoordinate low-spin heme is interpreted to involve the binding of His-52 at the distal site after the perturbation of the extensive H-bonded network within and around the heme pocket of CCP(II) at alkaline pH. Interestingly, CD investigations of CCP(II) in the far-UV and Soret regions indicate the dissappearance of a single high-spin species and the existence of at least two low-spin species of CCP(II) as the pH is raised above 7.90. Furthermore, transient resonance Raman experiments demonstrate that the hexacoordinate low-spin species can be photolyzed within 10-ns laser pulses, producing a species similar to the low-pH (high-spin) form of CCP(II) at alkaline pH. However, the extent of photolysis is quite pH dependent, with a maximum photodissociation yield at pH = 8.50.     

Proton nuclear Overhauser effect study of the heme active site structure of chloroperoxidase.

Chloroperoxidase, a glycoprotein from the mold Caldariomyces fumago, has been investigated in its ferric low-spin cyanide-ligated form through use of nuclear Overhauser effect (NOE) spectroscopy to provide information on the heme pocket electronic/molecular structure. Spin-lattice relaxation times for the hyperfine-shifted heme resonances were found to be three times less than those in horseradish peroxidase. This must reflect a slower electronic relaxation rate for chloroperoxidase than for horseradish peroxidase as a consequence of axial ligation of cysteine in the former versus histidine in the latter enzyme. Isoenzymes A1 and A2 of chloroperoxidase show the largest chemical shift differences near the heme propionate on the basis of NOE measurements. This suggests that the primary structure differences for the two isoenzymes are communicated to the heme group through the ring propionate substituents. A downfield peak has been detected in chloroperoxidase with chemical shift, T1, and line width characteristics similar to those of the C epsilon-H proton of the distal histidine residue. The NOE pattern and T1's of the peaks in the 0.0 to -5.0 ppm upfield region are consistent with the presence of an arginine amino acid residue in the heme pocket near either the 1-CH3 or 3-CH3 group. Existence of catalytically important distal histidine and arginine amino acid residues in chloroperoxidase shows it to be structurally similar to peroxidases rather than to the often compared monooxygenase, cytochrome P-450. This result supports the earlier conclusions of Sono et al. [Sono, M., Dawson, J.H., Hall, K., & Hager, L.P. (1986) Biochemistry 25, 347-356].     

Guanine residues in d(T2AG3) and d(T2G4) form parallel-stranded potassium cation stabilized G-quadruplexes with anti glycosidic torsion angles in solution.

We report below on proton NMR studies of the G-quadruplex structure formed by the human telomere sequence d(T2AG3) and the tetrahymena telomere sequence d(T2G4) in K cation containing solution. We observe well-resolved proton NMR spectra corresponding to a G-quadruplex monomer conformation predominant at 50 mM K cation concentration and a G-quadruplex dimer conformation predominant at 300 mM K cation concentration. By contrast, d(T2AG3T) and d(T2G4T) form only the G-quadruplex monomer structures independent of K cation concentration as reported previously [Sen, D., & Gilbert, W. (1992) Biochemistry 31, 65-70]. We detect well-resolved resonances for the exchangeable guanine imino and amino protons involved in G-tetrad formation with the hydrogen-bonded and exposed amino protons separated by up to 3.5 ppm. The observed NOEs between the amino and H8 protons on adjacent guanines within individual G-tetrads support the Hoogsteen pairing alignment around the tetrad. The imino protons of the internal G-tetrads exchange very slowly with solvent H2O in the d(T2AG3) and d(T2G4) quadruplexes. The nature and intensity of the observed NOE patterns establish formation of parallel-stranded right-handed G-quadruplexes with all anti guanine glycosidic torsion angles. A model for the parallel-stranded G-quadruplex is proposed which is consistent with the experimental NOE data on the d(T2AG3) and d(T2G4) quadruplexes in solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification and characterization of delta helicase from fetal calf thymus.

A DNA helicase (delta helicase) which partially copurifies with DNA polymerase delta has been highly purified from fetal calf thymus. delta helicase differs in physical and enzymatic properties from other eukaryotic DNA helicases described thus far. The enzyme has an apparent mass of 57 kDa by gel filtration and is associated with polypeptides of 56 and 52 kDa by SDS-polyacrylamide gel electrophoresis. Photo-cross-linking of the purified enzyme with [alpha-32P]ATP resulted in labeling of a polypeptide of approximately 58 kDa, suggesting that the active site is present on the larger polypeptide. Unwinding of a partial duplex requires a nucleoside triphosphate which can be either ATP or dATP but not a nonhydrolyzable analogue of ATP. Other ribo- and deoxyribonucleoside triphosphates have little or no activity as cofactors. delta helicase also has DNA-dependent ATPase activity which has a relatively low Km for ATP (40 microM). delta helicase binds to single-stranded DNA but has little or no affinity for double-stranded DNA or single-stranded RNA. Similar to replicative DNA helicases from prokaryotes and the herpes simplex virus type 1 helicase-primase, delta helicase translocates in the 5'-3' direction along the strand to which it is bound and preferentially unwinds DNA substrates with a forklike structure.     

Cloning of two adult hamster globin cDNAs (alpha and beta major).

A cDNA library was prepared from poly(A) mRNA extracted from adult anemic hamster spleen erythroid cells. cDNA clones containing inserts coding for adult alpha and beta major globin chains were isolated. Their identity was confirmed by (a) translation of hybrid selected mRNA and (b) nucleotide sequence analysis of the inserts and comparison to the adult globin cDNAs of mouse, rabbit and human. Availability of sequences for embryonic (Li et al. (1992) Biochim. Biophys. Acta 1130, 218-220) and adult globin cDNAs (this report) will aid in investigations of the molecular mechanisms involved in the globin ontogeny of hamsters.     

Intervention trial with selenium for the prevention of lung cancer among tin miners in Yunnan,China

This pilot study evaluated the feasibility and effectiveness of conducting a double-blind clinical trial for the prevention of lung cancer with selenium (Se) in Yunnan Tin Corporation, the People's Republic of China, where the incidence rates of lung cancer are extraordinarily high among the miners. Forty healthy miners were randomized to either 300 μg of Se in high Se malt cakes or an identical placebo of malt cakes daily for one year. Subjects consumed their usual daily diet. The low Se concentrations in plasma (0.05±0.008 μg/mL) and hair (0.442±0.085 μg/g) reflected their low dietary Se intake in the control subjects. In Se-supplemented group, the Se status was increased by 178% for serum and 194.8% for hair. The serum GSHpx activity was increased by 155.7%, whereas the lipid peroxide level was reduced by 74.5% compared to the placebo. The results of UDS assay indicated that the lymphocyte DNA damage induced by ultraviolet irradiation and carcinogen 3,4-benzpyrene could be protected by Se supplementation. Se-supplementation did not affect the liver function test (SGPT), as well as the concentrations of hemoglobin, albumin, and cholesterol. Thus, daily intake of 300 μg Se in form of Se-malt as a chemopreventive measure is safe and effective to humans with low Se status.     

Fractal analysis of protein chain conformation

This paper presents a simple practical method for characterizing conformation of protein chains. A single number Df, as the fractal dimension, is assigned to each chain. Df = Ln(N)/Ln(N.d/L), where N is the number of the amino acid residues in the chain, L and d are the total length and the planar diameter of the chain, respectively. In general, 1 less than Df less than or equal to 2, which is related to the shape of the protein chain. These values are different from those of Stapleton's group, but in agreement with computer simulations.     

Cloning and expression of a lignin peroxidase gene from Streptomyces viridosporus in Streptomyces lividans.

A lignin peroxidase gene was cloned from Streptomyces viridosporus T7A into Streptomyces lividans TK64 in plasmid pIJ702. BglII-digested genomic DNA (4-10 kb) of S. viridosporus was shotgun-cloned into S. lividans after insertion into the melanin (mel+) gene of pIJ702. Transformants expressing pIJ702 with insert DNA were selected based upon the appearance of thiostrepton resistant (tsrr)/mel-colonies on regeneration medium. Lignin peroxidase-expressing clones were isolated from this population by screening of transformants on a tsr-poly B-411 dye agar medium. In the presence of H2O2 excreted by S. lividans, colonies of lignin peroxidase-expressing clones decolorized the dye. Among 1000 transformants screened, 2 dye-decolorizing clones were found. One, pIJ702/TK64.1 (TK64.1), was further characterized. TK64.1 expressed significant extracellular 2,4-dichlorophenol (2.4-DCP) peroxidase activity (= assay for S. viridosporus lignin peroxidase). Under the cultural conditions employed, plasmidless S. lividans TK64 had a low background level of 2.4-DCP oxidizing activity. TK64.1 excreted an extracellular peroxidase not observed in S. lividans TK64, but similar to S. viridosporus lignin peroxidase ALip-P3, as shown by activity stain assays on nondenaturing polyacrylamide gels. The gene was located on a 4 kb fragment of S. viridosporus genomic DNA. When peroxidase-encoding plasmid, pIJ702.LP, was purified and used to transform three different S. lividans strains (TK64, TK23, TK24), all transformants tested decolorized poly B-411. When grown on lignocellulose in solid state processes, genetically engineered S. lividans TK64.1 degraded the lignocellulose slightly better than did S. lividans TK64. This is the first report of the cloning of a bacterial gene coding for a lignin-degrading enzyme.     

Preliminary study of the distribution of the toxic elements As,Cd, and Hg in human hair and tissues by RNAA

In order to study the relationships between trace element concentrations of hair and internal body burdens, a radiochemical NAA technique has been used for determination of the elements As, Cd, and Hg in autopsy samples of liver, kidney-cortex, lung, and hair from 24 male persons who died by accident. High significant positive correlations were observed between the As concentration in hair and in kidney-cortex, and between Cd and Zn concentrations in kidney-cortex. The contents of Cd, both for lung and kidney-cortex, were related to the smoking habits of the subjects.