强噪声对脑干听觉通路的影响

噪声暴露可造成听觉暂时性听阈偏移(TTS)和永久性听阈偏移。研究噪声对听觉中枢的影响对了解TTS的产生机制和防治噪声对听觉系统的损伤有重要意义。     

顶青霉D15木聚糖酶提纯及性质研究

经硫酸铵分级沉淀,BiO-gelP60凝胶过滤,和DEAE离子交换层析,从顶青霉D_15的麦麸培养物中提纯,得到4个具有凝胶电泳纯的木聚糖酶组分D_(x1)、D_(x2)、2_(x3)、D_(x4)、SDS—凝胶电泳法测得各个组分的分子量是:D_(x1),76000;D_(x2),4300;D_(x3),32500;D_(x4),29500。圆盘等电聚焦电泳法测得4个组分的等电点分别为4.50、5.70、5.30和5.20。热处理60分钟,D_(x1)、D_(x2),D_(x3)、D_(x4)的半失活温度分别为51.7℃、50.8℃、54.6℃和55.6℃。D_(x1)、D_(x4)在pH3.6—6.6稳定,D_(x2)和D_(x3)则在pH2.4—6.0稳定。各组分的A_(280)(1cm(?)mg/m1)分别是:D_(x1),0.97;D_(x2),1.46;D_(x3),0.98和D_(x4),1.07。     

刺皮属的二个新种

本文报道了银耳目银耳科刺皮属的二个新种——黄色囊状体刺皮(Heterochaete chryso-cystidiata Peng et X．W．Hu 和镰孢刺皮 (Heterochaete FALCATO-SPORIFERA Peng et X．W． Hu)。其形态特征,前者与中国刺皮 (Hererochaete sinensis Teng) 接近,但 H. chrysocysti- dtiara具有黄色囊状体(chrysocystidia)且担子和担孢子均较大;后者担子,担孢子的大小和形状及担子在子实层的排列方式颇接近 Bodman (1952)所描述的黑刺皮 H. nigerrima Viega-s.),但 H. falcato-sporifera 的子实体革质,白色,菌丝不具锁状联合．对这二个新种进行了汉文和拉丁文描述。所有新种的模式标本保藏于湖南师范大学真菌标本室(MHHNU)。     

种子的形成

种子是被子植物繁殖后代的器官,对人类来说是不可缺少的食物的重要来源。种子是由受精后的胚珠发育而来,它包含胚、胚乳(或缺少)及种皮。胚是幼小植物体的雏形,胚乳是作为胚生长的营养组织,而种皮是种子的保护结构。种子的这几部分是如何形成的呢?下面分别介绍。胚乳胚乳是胚囊中两个极核(或先融合     

小鼠小肠大剂量γ线照射的剂量-效应关系

三种不同种系的雄性、10周龄小白鼠于~(60)Co γ线照射10～100戈瑞(组距10戈瑞)72小时后活杀取出整个小肠,进行了小肠的长度、面积、重量的测量和全小肠纵切面切片中隐窝的计数。将上述指标的测量数据进行了统计学处理,并各配合了一条两项式的指数方程曲线。这些剂量一效应曲线都具有共同的双相性特点:即在饱和剂量(约为20戈瑞)以下时曲线较陡,而超过该剂量后曲线平直。在全小肠的纵切面切片中直接计数隐窝的方法,未见类似报道,文献中也无关于小肠面积在电离辐射作用后变化的观察。这两者都是对电离辐射的作用较为敏感的指标,操作简便,且均可进行较为精确的测量。     

柞蚕(Antherea pernyi)与桑蚕(Bombyx mori)丝心蛋白结构的研究

前言柞蚕与桑蚕丝心蛋白的结构在国外早已开始研究,但以研究丝心蛋白(Fibroin)与丝胶蛋白(Sericin)的氨基酸组成为多。近年来报道了桑蚕丝心蛋白结晶区多肽氨基酸组成,此种结晶区多肽含有组成该丝心蛋白的60%氨基酸,并主要为甘氨酸、丙氨酸、丝氨酸和酪氨酸等四种氨基酸重复排列形式。但未见报道柞蚕这方面     

Single amino-acid substitution in the N-terminal arm altered the tetramer stability of rat muscle lactate dehydrogenase A

Lactate dehydrogenase A (LDHA) is a well-characterized tetrameric enzyme. Its N-terminal arm, comprised of an α-helix and a β-strand, was suggested to be essential for subunit interactions. To examine the critical amino acid residues in the N-terminus involved in the subunit association, two single-point mutants, Leu3Pro (L3P) and Ile8Glu (I8E), have been constructed. We compared the stability of WT-LDHA (WT) and its variants by unfolding experiments. For WT, a dimeric but inactive intermediate was observed by size-exclusion chromatography at 0.6–0.8 mol/L GdmCl. Leu3Pro exists in an active tetrameric structure in aqueous solution as WT does, but it dissociates into dimers under lower concentration of GdmCl (0.2 mol/L). In aqueous solution, the Ile8Glu variant exists predominantly in the dimeric form with increased K_M and decreasedk _cat as compared with those of WT and L3P. However, the activity of Ile8Glu increases significantly in the presence of sodium sulfate. In conclusion, two mutants are less stable than WT in oligomer structure. Results also support the fact that some residues in the N-terminal arm, especially the Leu8 in the β-structure, contribute the important binding energies to the dimerization of dimers, which might affect the assembly of the enzyme as well as the catalytic function.