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31.
Quantum yields (φ) for the aerobic photolysis of 5′-deoxyadenosylcobalamin (dAB12), methylcobalamin (MeB12), propylcobalamin (PrB12), and ethylcobalamin (EtB12) were determined as a function of the irradiation wavelength. φ Determinations were made for both the base-on and base-off forms of each compound (except base-off dAB12) at incident wavelengths from 250 nm to 570 nm. As a rule, the φs were high (0.1–0.5) and they varied significantly with respect to the irradiation wavelength. In general, each alkylcobalamin at pH 7.0 displayed a quantum yield spectrum distinct from its base-off form at pH 1.0. Across most of the spectrum, the φs of the base-off form were appreciably smaller than the base-on φs of the same compound. An exception to this generality was MeB12 for which the φs at pH 1.0 were about the same as, or slightly greater above 450 nm than those at pH 7.0. At pH 7.0 and in the visible region the trend of the φs was dAB12 < MeB12 < PrB12 < EtB12. Under neutral conditions each compound showed a broad quantum yield peak in the 450–470 nm region.From the quantum yield and absorption spectra, photolysis spectra were calculated for 5.0 × 10?5m solutions of each compound. The light-action spectra accurately give the relative rates/μ Einstein that these solutions photolyze at each wavelength. Thus, for example, MeB12 photolyzed faster at pH 7.0 versus pH 1.0 in 510 nm light, but it photolyzed slower at pH 7.0 versus pH 1.0 in 450 nm light. Solutions of each compound photolyzed faster in the ultraviolet region as opposed to the visible (e.g., 310 nm versus 510 nm).Our findings show that the previously reported photolysis rates estimated by others with tungsten lamps provide no valid information about the intrinsic photolability of various alkyl-cobalt bonds. This also applies to the relative white-light photolysis rates reported for the base-on versus the base-off form of MeB12. All such relative rates are artifacts which represent only the extent of overlap between the true action spectrum and the light emission spectrum of an incandescent lamp. 相似文献
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C P Taylor 《Biochimica et biophysica acta》1977,491(1):137-148
A simple method is presented for calculating the parameters of the hole model for distorted octahedral, low spin (t2g)5 complexes. In the case of negligible covalent bonding explicit formulas for the coefficients of the Kramer's doublet, (formula: see text). The two numerically largest g values define the plane and orientation of the orbital with the largest coefficient, which in turn indicates the directions of maximal unpaired spin density. The energy of eta with respect to xi (in units of lambda, the spin-orbit coupling constant) is (formula: see text). The product gzgygx, independent of axes, and positive for free electrons, is shown to be positive for tetragonal and negative for nearly octahedral complexes. It is considered positive for hemes. In this method coefficients will only be normalized when there is no covalency. For the majority of published cases they are, to about 1%. Since this discrepancy is larger than can be caused by propagated errors, covalency must be the rule. For comparative purposes A and B, uncorrected for covalency, should still be useful. Examination of published complete g tensors for five hemes shows that the largest g value is nearly normal to the heme plane. If the g values are taken positive and labelled so that gz greater than gy greater than gx, then the proper tetragonal axis is roughly normal to plane of the ring in hemes, but not in chlorins. 相似文献
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Genes for serum amyloid A proteins map to Chromosome 7 in the mouse 总被引:10,自引:0,他引:10
Summary Several restriction fragment length variants have been detected among inbred strains using a mouse serum amyloid A cDNA clone. Five variants were shown to segregate as a single genetic unit and were mapped to Chromosome 7 between the glucose phosphate isomerase locus (Gpi-1) and the pink eye dilution locus (p) using recombinant inbred and congenic strains. The finding that no major MspI or BclI restriction fragments were shared between digests of DNAs from a Chromosome 7 congenic strain and its inbred partner, indicate that most, and probably all, sequences detected with the probe are clustered on Chromosome 7. Aneuploid mapping was used to show that the serum amyloid A gene complex (Saa) is proximal to the Chromosome 7 breakpoint in T(7;X)1Ct, a translocation in which the middle third of Chromosome 7 is inserted into the X-chromosome. A survey of inbred strains revealed a single common Saa haplotype and eight rare haplotypes. The complex distribution of 14 different variants suggests that recombination may have played a role in haplotype evolution.This work was supported by grants GM18684 and CA33093 from the National Institute of General Medical Sciences and the National Cancer Institute, respectively. 相似文献
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Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm−1 ). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required. 相似文献
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Vasant Chellappa Kendra N. Taylor Kathryn Pedrick Carlos Donado Ilka Arun Netravali Khaleda Haider Annaiah Cariappa Natasha F. Dalomba Shiv Pillai 《PloS one》2013,8(1)
Catalytically defective rare variants of Sialic acid Acetyl Esterase (SIAE) have previously been linked to autoimmunity. Studies presented here confirm that the M89V SIAE protein and all other products of common variant alleles of SIAE are catalytically normal. Although overexpressing transfected non-lymphoid cells secrete small amounts of SIAE that can associate with the cell surface, normal human lymphocytes do not exhibit cell surface SIAE, supporting genetic evidence in mice that indicates that this protein functions in a lymphocyte intrinsic manner. Analyses of the plasma proteome also indicate that SIAE is not secreted in vivo. A re-analysis exclusively of catalytically defective rare variant alleles of SIAE in subjects in which this gene was completely sequenced confirmed an association of SIAE with autoimmunity. A subset of catalytically defective rare variant SIAE alleles has previously been typed in a large genotyping study comparing a diverse group of disease subjects and controls; our re-analysis of this data shows that catalytically defective alleles are enriched in disease subjects. These data suggest that SIAE may be associated with autoimmunity and that further study of catalytically defective rare variant SIAE alleles in terms of autoimmune disease susceptibility is strongly warranted. 相似文献
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