染色体辐射效应的微机检测 Ⅱ断片率 微核率与细胞畸变率间的相关性检测

本文继前文后,按照设计的线性回归程序在“IBM—PC/XT”微型计算机上,进一步检测了断片率、微核率与细胞畸变率之间的相关性,肯定了微核测定法,断片测定法可以替代染色体畸变分析法。     

广东汉族健康人载脂蛋白AⅠ-CⅢl-AⅣ基因簇DNA多态性及其单倍型分布

本文研究了中国广东汉族健康人群apoAI-CⅢ-AIV基因簇DNA限制性内切酶PstI、SstI和EcoRI片段长度多态性。其中等位基因P_1,P_2,S_1,S_2,R_1和R_2的频率分别为0.98,0.02,0.96,0.04,0.90和0.10。经卡方检验符合Hardy-Weinbery氏遗传平衡,与其他种族比较,本文结果显示中国广东汉族人P_2等位基因频率低于日本人、亚洲印第安人和高加索人,S_2等位基因频率低于日本人、菲律宾人、沙特阿拉伯人和亚洲印第安人,而与高加索人相近,R_2等位基因频率稍高于高加索人。不同种族间apoAI-CⅢ-AIV基因簇DNA多态频率无疑存在差异,这种差异可能是由于遗传漂变和自然选择单独或联合作用所致。对P_1、P_2,S_1、S_2和R_1、R_2构成的单倍型和连锁平衡程度进行了分析,结果显示这些单倍型处于连锁不平衡状态。     

Sugars fermented byBifidobacterium infantis ATCC 27920 in relation to growth and α-galactosidase activity

Summary The ability of Bifidobacterium infantis ATCC 27 920 to ferment glucose, galactose, lactose, melibiose and raffinose was investigated with respect to -galactosidase (-d-galactoside galactohydrolase, E.C. 3.2.1.22). The sugars were tested at three concentrations: 0.5, 1.0 and 2.0%. The growth of B. infantis was slower on glucose compared with the other sugars. The highest specific growth rate was observed on melibiose followed by lactose. High cell numbers could be rapidly obtained on galactose-containing sugars. For each carbohydrate, enzyme activity was maximal at the end of the exponential phase and the highest specific -galactosidase activities were recorded on the two -1,6 galactosaccharides (melibiose and raffinose: 3.0 and 4.5 nkat · 10⁹ colony-forming units, respectively).Contribution no. 186 from the Food Research and Development Centre Offprint requests to: D. Roy     

Effects of medium composition on extracellular proteinase stability and yield in batch cultures of a Thermus sp.

Summary Thermus sp. Rt41A produces an extracellular proteinase that is produced concomitant with growth and l-glutamate catabolism. Calcium-chelating medium components were shown to decrease the half-life of the proteinase in growing cultures. Medium modifications avoiding these components resulted in an increase in the half-life and in the peak level of proteinase. By adding the inorganic phosphate requirement for growth in anabolic amounts to pH-controlled batch cultures, stability of the proteinase in the medium was greatly enhanced and there was consequent improvement in the total proteinase yield. This approach also allowed a balanced increase in substrate and phosphate concentrations to increase the cell and proteinase yield in batch culture in an almost stoichiometric manner.Offprint requests to: H. W. Morgan     

Aldimine to ketoamine isomerization (Amadori rearrangement) potential at the individual nonenzymic glycation sites of hemoglobin a: Preferential inhibition of glycation by nucleophiles at sites of low isomerization potential

The relative roles of the two structural aspects of nonenzymic glycation sites of hemoglobin A, namely the ease with which the amino groups could form the aldimine adducts and the propensity of the microenvironments of the respective aldimines to facilitate the Amadori rearrangement, in dictating the site selectivity of nonenzymic glycation with aldotriose has been investigated. The chemical reactivity of the amino groups of hemoglobin A forin vitro reductive glycation with aldotriose is distinct from that in the nonreductive mode. The reactivity of amino groups of hemoglobin A toward reductive glycation (i.e., propensity for aldimine formation) decreases in the order Val-1(), Val-1(), Lys-66(), Lys-61(), and Lys-16(). The overall reactivity of hemoglobin A toward nonreductive glycation decreased in the order Lys-16(), Val-1(), Lys-66(), Lys-82(), Lys-61(), and Val-1(). Since the aldimine is the common intermediate for both the reductive and nonreductive modification, the differential selectivity of protein for the two modes of glycation is clearly a reflection of the propensity of the microenvironments of nonenzymic glycation sites to facilitate the isomerization reaction (i.e., Amadori rearrangement). A semiquantitative estimate of this propensity of the microenvironment of the nonenzymic glycation sites has been obtained by comparing the nonreductive (nonenzymic) and reductive modification at individual glycation sites. The microenvironment of Lys-16() is very efficient in facilitating the rearrangement and the relative efficiency decreases in the order Lys-16(), Lys-82(), Lys-66(), Lys-61(), Val-1(), and Val-1(). The propensity of the microenvironment of Lys-16() to facilitate the Amadori rearrangement of the aldimine is about three orders of magnitude higher than that of Val-1() and is about 50 times higher than that of Val-1(). The extent of nonenzymic glycation at the individual sites is modulated by various factors, such as thepH, concentration of aldotriose, and the concentration of the protein. The nucleophiles—such as tris, glycine ethyl ester, and amino guanidine—inhibit the glycation by trapping the aldotriose. The nonenzymic glycation inhibitory power of nucleophile is directly related to its propensity to form aldimine. Thus, the extent of inhibition of nonenzymic glycation at a given site by a nucleophile directly reflects the relative role ofpK _a of the site in dictating the glycation at that site. The nonenzymic glycation of an amino group of a protein is an additive/synergestic consequence of the propensity of the site to form aldimine adducts on one hand, and the propensity of its microenvironment to facilitate the isomerization of the aldimines to ketoamines on the other. The isomerization potential of microenvironment plays the dominant role in dictating the site specificity of the nonenzymic glycation of proteins.     

Expedient syntheses of neoglycoproteins using phase transfer catalysis and reductive amination as key reactions

Starting from peracetylated chloro- or bromo-glycosyl donors ofN-acetylneurmainic acid,N-acetylglucosamine, glucose and lactose, the correspondingp-formylphenyl glycosides were synthesized stereospecifically under phase transfer catalysed conditions at room temperature in yields of 38–67%. After Zemplén de-O-acetylation, the formyl groups were directly and chemoselectively coupled to the lysine residues of bovine serum albumin by reductive amination using sodium cyanoborohydride. The conjugation reactions were followed as a function of time and under a series of different molar ratios of the reactants to provide glycoconjugates of varying degree of antigenicities. Thus, carbohydrate protein conjugates were made readily available using essentially two key reactions.Presented in part at the 15th International Carbohydrate Symposium, Yokohama, Japan, August 12–17, 1990.     

Maize chloroplast RNA polymerase: the 78-kilodalton polypeptide is encoded by the plastid rpoC1 gene.

The 180-, 120- and 38-kDa polypeptides found in highly purified maize plastid RNA polymerase preparations are encoded by the maize plastid genes rpoC2, rpoB, and rpoA, respectively [Hu, J. and Bogorad, L. (1990) Proc. Natl. Acad. Sci. USA. 87, pp. 1531-1535]. These genes have segments that specify amino acid sequences homologous to those of E. coli RNA polymerase subunits. The plastid gene products are designated b", b and a, respectively. We report here that the amino-terminal amino acid sequence of a 78-kDa polypeptide also found in highly purified maize plastid RNA polymerase preparations matches precisely the sequence deduced from the maize plastid rpoC1 gene which has segments homologous to the 5' end of the E. coli rpoC gene. Thus, the 78-kDa polypeptide is likely to be a functional component of maize plastid DNA-dependent RNA polymerase. This polypeptide is designated subunit b'. Three polypeptides unrelated to RNA polymerase have also been identified in this preparation.     

A novel translation initiation region from Mycoplasma genitalium that functions in Escherichia coli.

The tuf gene of Mycoplasma genitalium uses a signal other than a Shine-Dalgarno sequence to promote translation initiation. We have inserted the translation initiation region of this gene in front of the Escherichia coli lacZ gene and shown that it is recognized by the translational machinery of E. coli; the signal operates in vivo at roughly the same efficiency as a synthetic Shine-Dalgarno sequence. The M. genitalium sequence was also used to replace the native translation initiation region of the cat gene. When assayed in E. coli, the M. genitalium sequence is equivalent to a Shine-Dalgarno sequence in stimulating translation of this mRNA also. Site-directed mutagenesis enabled us to identify some of the bases that comprise the functional sequence. We propose that the sequence UUAACAACAU functions as a ribosome binding site by annealing to nucleotides 1082-1093 of the E. coli 16S rRNA. The activity of this sequence is enhanced when it is present in the loop of a stem-and-loop structure. Additional sequences both upstream and downstream of the initiation codon are also involved, but their role has not been elucidated.     

Antibodies to ovine adipocyte plasma membranes recognize tissue and species specific plasma membrane components

1. Ovine adipocyte plasma membrane (PM) contains three unique proteins that have relative molecular mass of 70, 106, and 110 kD which are lacking in PM from liver, kidney, heart, and red blood cells. 2. Two major proteins on ovine adipocyte PM having molecular mass of 44 and 46 kD which were also present on porcine adipocyte PM. 3. These ovine proteins could not be detected on either rat or chicken adipocyte PM.