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排序方式: 共有159条查询结果,搜索用时 15 毫秒
1.
The predominant form of phosphorylase phosphatase activity in porcine renal cortical extracts was a polycation-stimulated protein phosphatase. This activity was present in extracts in a high-molecular-weight form which could be converted to a free catalytic subunit by treatment with ethanol, urea, or freezing and thawing in the presence of beta-mercaptoethanol. The catalytic subunit of the polycation-stimulated phosphatase was purified by chromatography on DEAE-Sephacel, heparin-Sepharose, and Sephadex G-75. The phosphatase appeared to be homogeneous on SDS-polyacrylamide gel electrophoresis. The enzyme had an apparent Mr of 35 000 on gel filtration and SDS-polyacrylamide gel electrophoresis. The purified phosphatase could be stimulated by histone H1, protamine, poly(D-lysine), poly(L-lysine) or polybrene utilizing phosphorylase a as the substrate. It preferentially dephosphorylated the alpha-subunit of phosphorylase kinase. The phosphatase was highly sensitive to inhibition by ATP. These results suggest that the renal polycation-stimulated phosphatase catalytic subunit is very similar to or identical with the skeletal muscle phosphatase form which has been previously designated phosphatase-2Ac. 相似文献
2.
A major rabbit skeletal muscle phosphorylase phosphatase activity which is markedly stimulated by histone H1 has been resolved from inhibitor-sensitive phosphorylase phosphatase (type-1 phosphatase), glycogen synthase kinase 3-activated phosphatase, phosphatase heat-stable inhibitor proteins, and alkaline phosphatase activity by various purification techniques. Evidence is presented that this phosphatase is a high-molecular weight form of a type-2 phosphatase. Our data suggest that this phosphatase may be regulated by histone H1, protamine or analogous polycationic compounds. 相似文献
3.
Little is known about the relative intracellular localizations of the calcium-dependent proteases, calpains, and their naturally occurring inhibitor, calpastatin. In the present study, the intracellular localization of mu-calpain, m-calpain, and calpastatin was studied at the light microscopic level in proliferating A431 cells. Highly specific antibodies against the three antigens revealed distinct staining patterns in interphase and mitotic cells. Most notably, calpastatin in interphase cells was localized near the nucleus in tube-like, or large granular structures, while the calpains were more uniformly distributed through the cytoplasm in either a fibrillar form (mu-calpain) or a diffuse or fine granular form (m-calpain). The distribution patterns of the two calpain isozymes were distinctly different during mitosis. m-Calpain was concentrated at the mitotic spindle poles and midbody, while mu-calpain appeared to accumulate at the cell membrane and the spindles. Four other human cell lines as well as normal human monocytes were examined to determine if the calpains-calpastatin segregation patterns are common to other cells or are unique to the A431 line. With the exception of abundant nuclear mu-calpain in the C-33A cervical carcinoma, the segregation of the proteins was similar to that of A431. These studies indicate that calpains may be localized at regions which are relatively poor in calpastatin content. Proteins at these sites may be susceptible to calpain-catalyzed cleavage. 相似文献
4.
Neil R Brandt Anthony H Caswell Tara Brandt Keith Brew Ronald L Mellgren 《The Journal of membrane biology》1992,127(1):35-47
Summary The Ca2+ activated neutral protease calpain II in a concentration-dependent manner sequentially degrades the Junctional foot protein (JFP) of rabbit skeletal muscle triad junctions in either the triad membrane or as the pure protein. This progression is inhibited by calmodulin. Calpain initially cleaves the 565 kDa JFP monomer into peptides of 160 and 410 kDa, which is subsequently cleaved to 70 and 340 kDa. The 340 kDa peptide is finally cleaved to 140 and 200 kDa or its further products. When the JFP was labeled in the triad membrane with the hydrophobic probe 3-(trifuoromethyl) 3-(m) [125I]iodophenyl diazirine and then isolated and proteolysed with calpain II, the [125I] was traced from the 565 kDa parent to M
r, 410 kDa and then to 340 kDa, implying that these large fragments contain the majority of the transmembrane segments. A 70-kDa frament was also labeled with the hydrophobic probe, although weakly suggesting an additional transmembrane segment in the middle of the molecule. These transmembrane segments have been predicted to be in the C-terminal region of the JFP. Using an ALOM program, we also predict that transmembrane segments may exist in the 70 kDa fragment. The JFP has eight PEDST sequences; this finding together with the calmodulin inhibition of calpain imply that the JFP is a PEDST-type calpain substrate. Calpain usually cleaves such substrates at or near calmodulin binding sites. Assuming such sites for proteolysis, we propose that the fragments of the JFP correspond to the monomer sequence in the following order from the N-terminus: 160, 70, 140 and 200 kDa. For this model, new calmodulin sequences are predicted to exist near 160 and 225 kDa from the N-terminus. When the intact JFP was labeled with azidoATP, label appeared in the 160 and 140 kDa fragments, which according to the above model contain the GXGXXG sequences postulated as ATP binding sites. This transmembrane segment was predicted by the ALOM program. In addition, calpain and calpastatin activities remained associated with triad component organelles throughout their isolation. These findings and the existence of PEDST sequences suggest that the JFP is normally degraded by calpain in vivo and that degradation is regulated by calpastatin and calmodulin 相似文献
5.
R L Mellgren 《Biochimica et biophysica acta》1990,1040(1):28-34
The multicatalytic proteinase from human erythrocytes (macropain, proteasome) is a large enzyme composed of at least six distinct subunits ranging in molecular masses from 20 to 30 kDa. As its name implies, this proteinase appears to contain multiple catalytic sites with differing specificities toward peptide substrates. Several polycationic substances, including polylysines, polyarginine, protamine and histone H1 markedly stimulated caseinolytic activity of the proteinase. Activation was instantaneous, and involved increasing the Vmax of the proteinase for casein. Prolonged preincubation with polylysine at 37 degrees C resulted in autolytic inactivation of the proteinase. The polylysine concentrations required for half-maximal activation or autolytic inactivation were the same. A 23 kDa subunit of the proteinase disappeared at the same rate as loss of catalytic activity, and with the same pH dependence and polylysine concentration dependence. These results suggest that polylysine perturbs the structure of the multicatalytic proteinase, resulting in increased catalytic activity toward substrates; and, with prolonged exposure, allowing autoproteolytic inactivation to occur. The 23 kDa subunit appeared to be required for expression of caseinolytic activity, and may therefore be a catalytic subunit of the complex having activity against casein. 相似文献
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9.
Marianne Hauglid Fl?geng Stian Knappskog Ben P. Haynes Per Eystein L?nning Gunnar Mellgren 《PloS one》2013,8(8)
Cross-talk between the estrogen and the EGFR/HER signalling pathways has been suggested as a potential cause of resistance to endocrine therapy in breast cancer. Here, we determined HER1-4 receptor and neuregulin-1 (NRG1) ligand mRNA expression levels in breast cancers and corresponding normal breast tissue from patients previously characterized for plasma and tissue estrogen levels. In tumours from postmenopausal women harbouring normal HER2 gene copy numbers, we found HER2 and HER4, but HER3 levels in particular, to be elevated (2.48, 1.30 and 22.27 –fold respectively; P<0.01 for each) compared to normal tissue. Interestingly, HER3 as well as HER4 were higher among ER+ as compared to ER- tumours (P=0.004 and P=0.024, respectively). HER2 and HER3 expression levels correlated positively with ER mRNA (ESR1) expression levels (r=0.525, P=0.044; r=0.707, P=0.003, respectively). In contrast, EGFR/HER1 was downregulated in tumour compared to normal tissue (0.13-fold, P<0.001). In addition, EGFR/HER1 correlated negatively to intra-tumour (r=-0.633, P=0.001) as well as normal tissue (r=-0.556, P=0.006) and plasma estradiol levels (r=-0.625, P=0.002), suggesting an inverse regulation between estradiol and EGFR/HER1 levels. In ER+ tumours from postmenopausal women, NRG1 levels correlated positively with EGFR/HER1 (r=0.606, P=0.002) and negatively to ESR1 (r=-0.769, P=0.003) and E2 levels (r=-0.542, P=0.020). Our results indicate influence of estradiol on the expression of multiple components of the HER system in tumours not amplified for HER2, adding further support to the hypothesis that cross-talk between these systems may be of importance to breast cancer growth in vivo. 相似文献
10.
Monika H. E. Christensen Ellen M. Apalset Yngve Nordb? Jan Erik Varhaug Gunnar Mellgren Ernst A. Lien 《PloS one》2013,8(2)