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Two isoforms of a protease inhibitor were isolated by ion-exchange chromatography of tepary bean (Phaseolus acutifolius G.) seed proteins. The main isoform was used to determine the amino acid sequence of the protein. It is an 80 amino acid residue protein with a molecular mass of 8765 Da, showing sequence homology with the Bowman-Birk family of protease inhibitors. Several regions with amino acid microheterogeneity were found, corroborating the possible presence of isoforms. Mass spectrometry analysis was carried out to confirm isoforms. The presence of dimer and trimer forms of the inhibitor was shown through electrophoresis and mass spectrometry. Another unusual characteristic for this inhibitor was its ability to bind metals. The presence of four sequential histidines at the N-terminal end of the protein could account for this binding. Mass spectrometry and atomic absorption spectroscopy support the presence of calcium in the native inhibitor.  相似文献
2.
A high-affinity Zn(II)-binding protein has been purified to homogeneity (880-fold) from the plasma of lactating women by a single affinity adsorption step on columns of tris(carboxymethyl)ethylenediamine (TED)-agarose loaded with Zn(II) ions. Purity was evaluated by high-performance reverse-phase (phenyl) chromatography and by silver staining after SDS-polyacrylamide gradient gel electrophoresis. The mass of denatured Zn(II)-binding protein was estimated by SDS-polyacrylamide gradient gel electrophoresis to be 75 kDa under both reducing and nonreducing conditions; by matrix-assisted uv laser desorption time-of-flight mass spectrometry the purified protein mass was determined to be 66 kDa. The amino acid composition revealed a high content of His (13 mol%) and Pro (12 mol%). N-terminal amino acid sequence analysis (50 residues) identified the purified protein as histidine-rich glycoprotein (HRG). Immunoblots demonstrated the absence of fragments in the purified product. An enzyme-linked immunosorbent assay was developed; a 75% recovery of intact HRG from the immobilized Zn(II) ion affinity column was documented. The circular dichroism spectra for the purified human HRG in the far uv (260-178 nm) were similar to those published for human and rabbit serum HRG. These results demonstrate that TED-immobilized Zn(II) ions can be used as a new and efficient method for the isolation of structurally intact human plasma HRG.  相似文献
3.
Summary Enterocytes of the small intestine in 1-day-old suckling piglets contain numerous vesicles in the apical cytoplasm and a large granule located beneath the nucleus. Within the next 3 days, these granules transform into electron-dense crystalloid inclusions. These membrane-bound inclusions are up to 10 m in length and 1–2 m in diameter, and they are composed of electron-dense lamellae 3.9 nm apart. Postembedding immunocytochemistry, using rabbit anti-porcine IgG and goat anti-rabbit IgG conjugated to 10 nm colloidal gold, revealed that both the granules and the crystalloid inclusions contained a high concentration of maternal IgG. Although the IgG content of the crystalloid inclusions was detected on epoxy-embedded sections, the use of LR White resin resulted in a much higher density of labelling. Quantification of the labelling density showed that the concentration of IgG in the crystalloid inclusions was approximately ten times higher than that in the lumenal colostrum and approximately three times higher than that in the granules. These observations showed that there are at least three compartments involved in the accretion of IgG in the small intestine of neonatal piglets: smaller apical endocytotic vesicles, large subnuclear granules and crystalloid inclusions. The role of these compartments in maternal immunoglobulin absorption and in the acquisition of passive immunity has yet to be explored.  相似文献
4.
This article describes the technique of immobilized metal ion affinity chromatography (1MAC). The IMAC stationary phases are designed to chelate certain metal ions that have selectivity for specific groups in peptides and on protein surfaces. The number of stationary phases that can be synthesized for efficient chclation of metal ions is unlimited, but the critical consideration is that there is enough exposure of the metal ion to interact with the proteins, preferably in a biospecific manner. The versatility of IMAC is one of its greatest assets. An important contribution to the correct use of IMAC for protein purification is a simplified presentation of the various sample elution procedures.  相似文献
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