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Graham S. Baldwin Alphonse Galdes H.Allen O. Hill Stephen G. Waley Edward P. Abraham 《Journal of inorganic biochemistry》1980,13(3):189-204
β-Lactamase II has two metal-binding sites. The electronic spectra of Cd(II)- and Co(II)-substituted β-lactamase II have been investigated. It is suggested that a thiol ligand is involved in metal binding at the first site. The stoichiometric dissociation constants for Co(II) binding to β-lactamase II were estimated to be 0.13 and 2.66 mM (pH 6.0, 4°C, 1 M NaCl) by equilibrium dialysis. Competition between Zn(II) and Co(II) for the first metal binding site suggests a value of 0.7 μM (pH 6.0, 30°C, 1 M NaCl) for the dissociation constant o Zn(II).The electronic spectra of the Co(II) enzyme lead to the suggestion that the coordination geometries around the metal ions in the first and second sites are related to those of a distorted tetrahedron and octahedron, respectively. 相似文献
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The “Hill” equation for co-operative binding-systems has been extended to describe the effect of substrate-analogue on the binding of substrate to an oligomeric protein. It is demonstrated that the more negatively co-operative the binding-system, the more sensitive is the binding of substrate to inhibition by increases in the relative concentration of substrate-analogue. It is proposed that the physiological significance of negative co-operativity for enzymes may be complementary to the physiological significance of positive co-operativity. The effect of negative co-operativity is to make substrate binding more sensitive to inhibition by relative increases in the concentration of substrate-analogue (e.g. for many enzymes product of the reaction) at the expense of decreased sensitivity of substrate binding to relative changes in substrate concentration compared to a system with equivalent, independent substrate binding sites. In contrast, the effect of positive co-operativity is to make the enzyme more sensitive to relative changes in substrate concentration at the expense of decreased sensitivity to inhibition by relative increases in product concentration, compared to an enzyme without co-operative binding. 相似文献
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Abstract A total of 1599 stoats were collected from 14 study areas (including all 10 National Parks) from 1972 to 1976. Samples were larger in summer, and contained more females. Young stoats are born in September-October, and females reach adult weight by the following March, though males not until after August. There was significant geographic variation in the body size of adult stoats sampled: males from lowland podocarp/broadleaved forests averaged 3% smaller than males from upland beech forests in skull length, and 4% smaller in head-and-body length. This pattern was repeated, less clearly, in females and in young (approximately 2–5 months old). In contrast with stoats in Britain, assumed to be still the same size as the colonising stock introduced into New Zealand in 1884 and subsequently, males from lowland podocarp forests were unchanged or possibly smaller, and males from upland beech forests were larger; females were larger in all habitats. In males, the extent of geographic variation is almost as great in New Zealand as in the whole of continental Europe. Possible explanations of this pattern are discussed. 相似文献
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Spencer E. Taylor Erwin Buncel Albert R. Norris 《Journal of inorganic biochemistry》1981,15(2):131-141
Proton nmr spectroscopic evidence is presented for methylmercury(II) binding to the deprotonated amino groups in adenosine, 9-methyladenine, guanosine, 1-methylguanosine, and cytidine under basic conditions. Except for the guanosine case, 1H nmr spectra of the products from aqueous or ethanolic 1:1 mixtures of substrate and MeHgOH are consistent with methylmercuration of the deprotonated amino groups. Guanosine undergoes initial binding of MeHg to N1, and a second equivalent of MeHgOH is necessary to effect amino binding. The nmr spectra of the complexed adenine derivatives suggest that different geometrical isomers exist in (CD3)2SO solution, reflecting the partial double bond character of the C6N bond in these systems. Using a correlation relating the magnitude of the 199Hg-1H coupling constant (J) for MeHg-ligand complexes with the ligand pKa (J = ?3.88 pKa + 248.5, extending over 13 pK units, based on a variety of N and O donor ligands), estimates (± 0.3 pK unit) of the pKas of the amino groups of the above substrates have been made. In this way, pKa values of 15.5 (cytidine), 17.0 (adenosine and 9-methyladenine), 15.1 (guanosine), and 14.9 (1-methylguanosine) are obtained. In the cases where comparisons with literature pKa data can be made, good agreement is found. 相似文献
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G. Venturella M. L. Gargano R. Compagno A. La Rosa E. Polemis G. I. Zervakis 《Plant biosystems》2016,150(5):1030-1037
An investigation on the macrofungal diversity of the National Park “Appennino Lucano, Val D'Agri, Lagonegrese” (Basilicata, southern Italy) was carried out, together with an evaluation of wild edible mushrooms in agro-forest ecosystems and their possible exploitation as a new source of food and revenue in rural and under-developed areas of this region. An unpublished list of 249 mushroom taxa (229 Basidiomycota and 20 Ascomycota), mostly belonging to the genera Tricholoma, Tuber, Russula, Amanita, Boletus, Lactarius, Mycena, Agaricus, Clitocybe and Hygrophorus, growing in this important natural area is provided together with ecological characterization of the recorded specimens. Inonotus obliquus is a new record for Basilicata, while Mycena bresadolana is reported for the first time from southern Italy. The presence of Amaurodon mustialaënsis, an extremely rare species of the northern hemisphere reported for the first time on white fir, is noteworthy. Among the previous findings, 116 species of edible mushrooms are presented and discussed in view of their relative abundance and edibility. 相似文献
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Nuclear magnetic resonance studies of the phenylalanine residues of eukaryotic cytochrome c 总被引:3,自引:0,他引:3
A P Boswell G R Moore R J Williams J C Chien L C Dickinson 《Journal of inorganic biochemistry》1980,13(4):347-352
The resonances of Phe 82 and Phe 10 in the nuclear magnetic resonance spectra of horse cytochrome c are reassigned using nuclear Overhauser enhancements. The reassignments provide new information about the oxidation state linked conformation change of cytochrome c. The region of the protein now known to be affected by the change extends to the part of the protein close to Phe 10. 相似文献
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The binding of[Co(CN)6]3?, and that of[Fe(CN)6]3? and [Ru(CN)6]4? using a competitive method, to horse cytochrome c has been studied by 59 Co NMR spectroscopy. At I = 0.07 M, without added salt and in 2H2O at ph* 7.3 (measured in 2H2O) and 25°C, there are at least two binding sites on ferricytochrome c and ferrocytochrome c for [Co(CN)6]3?. Association constants were determined to be 2.0 ± 0.6 × 103M?1 and 1.5 ± 0.5 × 102M?1 respectively. with no effect of the oxidation state of the cytochrome. At higher ionic strength (I = 0.12 M adjusted with KCl the binding markedly decreased, and, although it was not possible to determine the precise binding stoichiometry and magnitude of association constants, it is clear that the association constants are ≤ 1.5 × 10tM?1 The binding of [Ru(CN)6]4? at I = 0.07, without added salt and in 2H2O at pH 1.3 and 23°C, was not precisely defined, but its binding strength relative to that of [Fe(CN)6]3? was determined. Extrapolating this to I = 0.12 (KCl) suggests that under these conditions the association constant for [Ru(CN)6]4? binding to ferricytochrome c is ≤ 3 × 102M?1. 相似文献
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Strengthening the Natural and National Park system of Iberia to conserve vascular plants 总被引:3,自引:0,他引:3
ISABEL CASTRO PARGA JUAN CARLOS MORENO SAIZ CHRISTOPHER J. HUMPHRIES PAUL H. WILLIAMS 《Botanical journal of the Linnean Society. Linnean Society of London》1996,121(3):189-206
The diversity of the Iberian vascular flora has been investigated using WORLDMAP versions 3.08 and 3.18. Two data sets scoring plant distributions as presences within the Iberian Peninsula were compiled; one for 2133 species at 50 × 50 km grid and the other for 801 species at 10 × 10 km map grids. Patterns of biodiversity were determined using the diversity measures of species richness, range-size rarity and character richness diversity. Using the diversity measures, combined with an area selection method, maps of priority areas were calculated using iterative procedures. Near minimum sets (NMSs) for both scales were calculated. Comparison of the NMS for the 10 × 10 km grid with the near minimum set for existing reserves (NMSER) showed that at least 2% more of the land surface would be required above and beyond the existing protected area network, currently comprising 6% of the area, to ensure representation of all species at least once as listed within the present data-base. It is demonstrated that reserve systems selected on a variety of different criteria are suboptimal when compared to particular groups of target organisms with a definite goal of representation for conservation. Calculating efficiency of existing reserve systems and accounting for all taxa identifies precisely the extra required areas for the protected area system to satisfy particular goals of representation. 相似文献