Conformational analysis of CCK-B agonists using 1H-nmr and restrained molecular dynamics: Comparison of biologically active Boc-Trp-(N-Me)Nle-Asp-Phe-NH2 and inactive Boc-Trp-(N-Me)Phe-Asp-Phe-NH2

The tetrapeptide Boc-Trp-(N-Me)Nle-Asp-Phe-NH₂ is a potent CCK-B agonist. Replacement in this analogue of the norleucine residue by a phenylalanine, to yield Boc-Trp-(N-Me)Phe-Asp-Phe-NH₂, led to a 740-fold decrease in affinity whereas the same decrease in affinity was not observed in their nonmethylated counterparts. In order to ascertain the conformational preferences of these two N-methylated tetrapeptides, a study by two-dimensional (2D) nmr spectroscopy and molecular modeling was undertaken. The solution conformation of the two peptides was examined by ¹H-nmr in a d₆-DMSO/H₂O (80 : 20) mixture. A cis-trans equilibrium, induced by N-methylation, was observed for both analogues, and the proton spectra of the two retamers were fully characterized in each case. ¹H-¹H distance constraints, derived from 2D nuclear Overhauser effect spectroscopy and rotating frame nuclear Overhauser effect spectroscopy experiments, were used as inputs for subsequent restrained molecular dynamics simulations. Comparisons of the nmr and molecular modeling data point toward distinct conformational preferences for these two peptides with an opposite spatial orientation of the Trp residue, and could explain the large difference in their biological activities. Furthermore, the tridimensional structure of Boc-Trp-(N-Me)Nle-Asp-Phe-NH₂ could serve as a model for the design of nonpeptide CCK-B agonists. © 1994 John Wiley & Sons, Inc.     

中国九个人群耵聍的遗传多态性

报道了九个人群的耵聍位点基因。计算表明中国各族人群在耵聍位点上的遗传分化程度非常大,固定指数F_(ST)=0.22。本文根据耵聍基因频率在我国和邻近地区的分布趋势,认为亚洲东北地区应是干型基因的起源地,目前世界上耵聍位点基因频率分布格局主要是基因扩散的结果,而非选择作用造成的。     

The kinetics of the first wave of spermatogenesis in the newborn male mouse

A combination of autoradiography and air-dried techniques was used to calculate the duration of the major meiotic stages in the first wave of spermatogenesis in the newborn mouse. The data indicated that the entry into meiosis occurred asynchronously over 2 days, and the time required for each stage and the total cycle was constant. These time intervals were nearly identical with those estimated for adult animals in the present study and by other authors.     

DETERMINATION OF GUSTATORY SUCROSE THRESHOLD IN WATER BY USE OF A LINEAR SUCROSE GRADIENT

A novel experimental method was developed which allows the determination of the threshold concentration of sucrose by use of a linear sucrose gradient in water. With this method a continuous tasting of the test-liquid is possible. A panel of 15 persons experienced in taste-testing was used. Three gradients of different steepness were applied: 0 to 1.5% (w/w) sucrose in 2 min (I), 3 min (II) and 4 min (III). The results of the new method were compared with those of the standard method (DIN). With gradients I and II we found values which were significantly higher than those of the standard method (I: 0.49% (w/w); II: 0.46% (w/w); DIN: 0.31% (w/w)), whereas with gradient III the same threshold value was found as with the DIN-Method (III: 0.32% (w/w)).     

Development and validation of a high-performance liquid chromatographic method for the determination of methocarbamol in human plasma

An isocratic HPLC method was developed and validated for the quantitation of methocarbamol in human plasma. Methocarbamol and internal standard in 200 μl of human plasma were extracted with ethyl acetate, evaporated to dryness and reconstituted in water. Separation was achieved on a reversed-phase C₁₈ column with a mobile phase of methanol—0.1 M potassium phosphate monobasic—water (35:10:55, v/v/v). The detection was by ultraviolet at 272 nm. Linearity was established at 1–100 μg/ml (r > 0.999). The limit of quantitation was designed as 1 μg/ml to suit pharmacokinetic studies. Inter-day precision and accuracy of the calibration standards were 1.0 to 3.6% coefficients of variance (C.V.) and −2.0 to +1.6% relative error (R.E.). Quality controls of 3, 20 and 70 μg/ml showed inter-day precision and accuracy of 2.5 to 3.6% C.V. and −0.9 to −0.4% R.E. Recovery of methocarbamol was 91.4–100.3% in five different lots of plasma. The method was shown to be applicable on different brands of C₁₈ columns.     

Crystal structure of human annexin I at 2.5 A resolution.

cDNA coding for N-terminally truncated human annexin I, a member of the family of Ca(2+)-dependent phospholipid binding proteins, has been cloned and expressed in Escherichia coli. The expressed protein is biologically active, and has been purified and crystallized in space group P2(1)2(1)2(1) with cell dimensions a = 139.36 A, b = 67.50 A, and c = 42.11 A. The crystal structure has been determined by molecular replacement at 3.0 A resolution using the annexin V core structure as the search model. The average backbone deviation between these two structures is 2.34 A. The structure has been refined to an R-factor of 17.7% at 2.5 A resolution. Six calcium sites have been identified in the annexin I structure. Each is located in the loop region of the helix-loop-helix motif. Two of the six calcium sites in annexin I are not occupied in the annexin V structure. The superpositions of the corresponding loop regions in the four domains show that the calcium binding loops in annexin I can be divided into two classes: type II and type III. Both classes are different from the well-known EF-hand motif (type I).     

正常人各年龄组染色体着丝粒点(Cd)研究

本文运用本室改良的Cd-NOR银染技术对80例4个年龄组的正常中国人的Cd变化进行了较系统的研究, 结果表明:(1)正常人随年龄增加,Cd消失的频率、Cd变异及Cd-NOR融合频率也相应增加,特别是Ⅲ、Ⅳ组(中、老年组)增加的频率尤为显著;(2)首次对Cd消失的过程提出了独特的观点,即Cd消失首先表现为Cd变小, 随着变小程度的加大,最终导致Cd消失;(3)在本研究中首次观察到单个Cd的现象,作者认为是细胞分裂中期染色体着丝一分为二的延迟现象。各年龄组间单Cd出现频率无统计学差异,同一年龄组中,2号染色体和1号染色体上单Cd出现频率显著高于理论值;(4)随年龄增高,Cd各项观察值的增高在男性与女性间未见明显的差异。 Abstract:The Cd variation of human chromosome in four groups of different age has been investigated.The result shows that the frequencies of Cd disappearing,size variation and Cd-NOR fusion increased with the age rising,especially in the group of aged people.We suggest that the variation of Cd shows the size changes first,and then disappears completely.We also observed some cells in which a few chromosomes shows only a single Cd in centromeric region.Cd variation in different age groups has no significant difference between the male and the female.     

Preparation of enteric-coated microspheres of Mycoplasma hyopneumoniae vaccine with cellulose acetate phthalate: The effect of swine serum on micromeritic properties

Summary Cellulose acetate phthalate was used to prepare the Mycoplasma hyopneumoniae vaccine (MHV) microspheres using a solvent evaporation method. Swine serum was used as an additive in the antigen to form the core materials. The addition of serum had a significant effect on surface topography of the MHV microspheres. By using this modified solvent evaporation method, the recoveries of antigens in the MHV microspheres were generally over 90% of the weight and antigenicity of antigens originally added in the formulation.