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31.
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转铁蛋白结构与功能的研究——骆驼血清转铁蛋自的分离纯化及其含单一铁结合部位的结构域的制备和鉴定 总被引:1,自引:0,他引:1
分离纯化获得的骆驼血清转铁蛋白由分子量为73,000和63,000两个组分组成。两者至少N-端五肽顺序相同(Met-Pro-Asp-Lys-Thr)。骆驼血清转铁蛋白在生理pH下不能与人胎盘转铁蛋白受体结合。用胰蛋白酶酶解骆驼转铁蛋白可以同时得到两个合单一铁结合部位的结构域,分别来自转铁蛋白分子的N-端称N-端结构域(分子量34,700和40,700)和C-端称C-端结构域(分子量35,100)。在上述结果的基础上指出并讨论了反刍动物转铁蛋白在结构和功能上存在更多的共同性,而与其它哺乳动物的转铁蛋白有着明显的区别。 相似文献
33.
The effect of high supercoil densities on the melting characteristics of a supercoiled DNA has been studied. It is found that although the melting temperature increases abruptly on converting a linear DNA merely into the relaxed circular form, it falls back substantially at high supercoil densities. It is further predicted, in such cases, that the number of melted base pairs should be significantly enhanced even at the physiological temperature, which may facilitate the binding of other molecules to the highly supercoiled DNA. 相似文献
34.
Bhabesh Sen Franklin A. Graybill Naitee Ting 《Biometrical journal. Biometrische Zeitschrift》1992,34(3):259-274
The model considered in this article is the two-factor nested unbalanced variance component model: for p = 1, 2, …, P; q = 1, 2, …, Qp; and r = 1, 2, …, Rpq. The random variables Ypqr are observable. The constant μ is an unknown parameter, and Ap, Bpq and Cpqr are (unobservable) normal and independently distributed random variables with zero means and finite variances σ2A, σ2B, and σ2C, respectively. Approximate confidence intervals on ?A and ?B using unweighted means are derived, where The performance of these approximate confidence intervals are evaluated using computer simulation. The simulated results indicate that these proposed confidence intervals perform satisfactorily and can be used in applied problems. 相似文献
35.
An X-prolyl dipeptidyl aminopeptidase (X-PDAP; EC 3.4.14.5) was identified to be loosely bound on the inner cell membrane fraction of Lactococcus lactis subsp. cremoris nTR. The biosynthesis of X-PDAP was continuously increased before the late-log growth phase of the bacteria. Both Gly-Pro-pNA and Ala-Ala-pNA were hydrolyzed by X-PDAP; the kcat/Km value of the former was about 10-fold that of the latter. The Ki of X-Pro and Pro-X were more specific to X-PDAP than those of X-Ala. The enzyme splitting a dipeptide sequentially from beta-casomorphin as a model catalytic pattern was identified and some properties of the enzyme were further characterized. 相似文献
36.
In previous studies, we have demonstrated the differences in thermotolerance induced by heat and sodium arsenite (Lee et al., Radiat. Res. 121, 295-303, 1990). In this study, we investigated whether a 26-kDa protein might play an important role in evincing these differences. Chinese hamster ovary (CHO) cells treated for either 1 h with 100 microM sodium arsenite (ARS) or 10 min at 45.5 degrees C became thermotolerant to a test heat treatment at 43 degrees C administered 6 or 12 h later, respectively. After the test heating at 43 degrees C for 1.5 h, the level of 26-kDa protein in the nucleus was decreased by 92% in nonthermotolerant cells, 78% in ARS-induced thermotolerant cells, and 3% in heat-induced thermotolerant cells. Inhibiting protein synthesis with cycloheximide (CHM, 10 micrograms/ml) after ARS treatment eliminated thermotolerance to 43 degrees C and delayed restoration of the 26-kDa protein in the nucleus. In contrast, CHM neither prevented the development of thermotolerance nor inhibited the restoration of the 26-kDa protein in heat-induced thermotolerant cells. However, when cells were exposed to cold (4 degrees C), immediately after initial heating, restoration of the 26-kDa protein and development of thermotolerance did not occur. These results demonstrate a good correlation between the restoration and/or the presence of this 26-kDa protein and the development of protein synthesis-independent thermotolerance. 相似文献
37.
人肌肌酸激酶胍变性时的失活与构象变化的比较研究 总被引:1,自引:1,他引:0
应用二阶导数光谱、紫外差吸收光谱和荧光光谱等监测手段,研究了人肌肌酸激酶在盐酸胍溶液中的构象变化。二阶导数光谱结果表明,若以6M盐酸胍中肌酸激酶酪氨酸残基的暴露程度为100%,则天然酶酪氨酸残基的暴露程度只有2%。而紫外差吸收光谱和荧光光谱的变化与兔肌肌酸激酶的结果相似。比较不同胍浓度下人肌肌酸激酶的失活与构象变化,表明酶的失活先于构象变化。同时还测定了不同浓度胍溶液中人肌酶的失活与构象变化的速度常数。结果表明以几种方法测定的构象变化均为单相的一级过程,而酶的失活却呈现了由快慢两相组成的一级反应过程。比较同浓度胍溶液中的失活速度与构象变化速度,发现酶失活的快相反应速度常数比构象变化的速度常数大1—2个数量级,慢相速度常数与构象变化速度常数相近。上述结果进一步支持了酶的活性部位构象柔性的观点。 相似文献
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将去除信号肽的人肿瘤坏死因子-α(Tumor necrosis factor-α,TNF-α)cDNA插入到带有原核增强子样序列Px的新型表达载体pBV320中,使TNF cDNA 5′端直接置于大肠杆菌trp启动子下游,采用37℃恒温培养,使TNF在大肠杆菌中获得了高效表达,表达活性达1.35(±0.17)×10~6U/L菌液。表达的TNF-α对L929细胞的毒性作用可被抗人肿瘤坏死因子-α的单克隆抗体所中和。表达菌裂解液作SDS-聚丙烯酰胺凝胶电泳,显示有一条分子量与TNF分子量吻合、约为17000道尔顿的蛋白带。利用DEAE-Sepharose阴离子交换层析及Sephacryl S-200凝胶过滤对上述重组人TNF-α进行纯化,获得电泳纯产品,比活性为1.48×10~6U/mg。 相似文献