水稻高脯氨酸愈伤组织变异体盐胁迫下氨基酸和蛋白质组分的变化

游离氨基酸组分分析表明,水稻培养细胞中谷氨酸和丙氨酸含量很高,占氨基酸总量的４０％。高脯氨酸愈伤组织变异体总游离氨基酸含量比原型高４５．５％,其中脯氨酸增加最多,其次是雨氨酸和谷氨酸。当ＮａＣｌ１００ｍｍｏｌ／Ｌ处理时变异体和原型的总氨基酸都增加,而变异体的增量约为原型增量的３倍。蛋白水解氨基酸组分中变异体和原型各氨基酸的相对含量无大差异。蛋白质双向电泳表明,高脯氨酸变异体的蛋白组分发生变化,明显比原型多４个蛋白点。在ＮａＣｌ１００ｍｍｏｌ／Ｌ处理下原型亦产生５３．３ｋＤ蛋白,变异体中该蛋白的含量变得更多。盐胁迫下变异体和原型的蛋白质组分变化的差异十分显著,主要表现在蛋白质等电点的变化不同。     

Salt tolerance of pigeon pea (Cajanus cajan (L.) Millsp.) at three growth stages

Salt tolerance of pigeon pea (Cajanus cajan (L.) Millsp.) was determined at three growth stages following observations by a number of workers that degree of salt tolerance of different crops varies with their ontogeny. The salt tolerance of three accessions, Local arhar, ICPL-151 and ICPL-850014 of pigeon pea was assessed at the germination, seedling and adult stages. There was no positive correlation between tolerance at the early growth stages and at the adult stage since no clear difference in salt tolerance of the three accessions was observed at the germination and the seedling stages, whereas accessions differed considerably at the adult stage. Although increasing salt concentrations adversely affected the growth of all three accessions, ICPL-151 was superior to the other two accessions in fresh and dry biomass, yield and yield components when tested at the adult stage. The tolerant accession, ICPL 151, accumulated significantly lower Na⁺and CI in shoots. By contrast it was higher in shoot and root K⁺, K/Na ratios, K vs Na selectivity, soluble sugars, free amino acids and proline compared with the other two accessions.     

Consequences of a tidal reduction for the salt-marsh vegetation in the Oosterschelde estuary (The Netherlands)

A storm-surge barrier was constructed in the mouth of the Oosterschelde, a euhaline mesotidal estuary in the SW Netherlands (mean tidal range 3.6 m). As a consequence, the tidal range and the Mean High Water in the estuary have been reduced to about 88% of their original values.During the final construction stage of this barrier (1986–87) both were reduced to a maximum of 65% for more than 18 months. During this period, large-scale die-back of the vegetation occurred in vast areas on the salt marshes; locally, a complete die-back of the vegetation took place. Glycophytes and disturbance indicating species appeared on a large scale and grew abundantly. After the new tidal regime had been established, the vegetation recovered. The species characteristic of disturbance, are gradually being replaced by perennial salt marsh species. In addition, most species are shifting into zones of lower elevation, which correspond (in 1990/1991) more or less with the original flooding frequencies. Moreover, in many basins the levee-species Halimione portulacoides and Elymus pycnanthus are far more prominent than before, probably as a result of the strong ripening of the soil that has occurred in these basins during the extra tidal reduction. In 1991, four years after the establishment of the new tidal regime, the salt marsh vegetation had still not been stabilized.     

Side reactions in the synthesis of phosphotyrosine-containing peptides

Summary A series of phosphopeptides Tyr(PO₃H₂)-Val-Pro-Xxx-Leu (Xxx=Met, Met(O), Nle, Dab or Cys), derived from the native platelet-derived growth factor- receptor (PDGF-) sequence, has been prepared to study their interaction with the src-homology 2 (SH2) domains of the p85 subunit of PI3 kinase. The phosphopeptides were synthesized using Fmoc methodology incorporating N-Boc dibenzyl-protected phosphotyrosine (Boc-Tyr[PO₃(Bzl)₂]) as the N-terminal amino acid, since the benzyl groups can be removed during resin cleavage with TFA. Only peptides containing methionine were found to exist partially as S-benzyl sulfonium salts after TFA cleavage from the resin. The desired peptide could be obtained from the S-benzyl sulfonium salt by hydrogenolysis.     

Peptide crystal growth via sulfonate salt formation: The structure of bis-glycylglycine-1,5-naphthalenedisulfonate hydrate

Summary Continuing a line of investigations on methods for formation and growth of high-quality crystals of peptides, the glycylglycine sequence has been crystallized by evaporation methods as a salt with 1,5-naphthalenedisulfonic acid. The structure of the peptide is highly extended, and is conformationally quite similar to the structures which have been characterized for other zwitterionic and salt forms of this sequence. Thus, crystallization as a salt with this sulfonic acid has imposed no undue influence upon the molecular conformation. These results offer further indication that the preparation of peptide sulfonate salts, particularly with arene templates, may have broad general utility for crystallization of interesting sequences which until now have not been approachable in their zwitterionic forms.     

Chirospecific synthesis of D and Lp-chlorohomophenylalanine N-t-BOC DCHA salts

Summary The chirospecific conversions of D-glucosamine hydrochloride and D-mannosamine hydrochloride to the configurationally stable L and D isomers of N-t-butyloxycarbonylserinal were carried out byt-butylcarbonylation followed by sodium borohydride reduction and sodium meta-periodate oxidation. Reaction of the L and D aldehydes with the Wittig reagent prepared from 4-chlorobenzyltriphenylphosphonium chloride and butyl lithium followed by catalytic hydrogenation, Jones oxidation and salt formation with dicyclohexylamine gave the DCHA salts of the D and L isomers ofp-chlorohomophenylalanine N-t-Boc in high enatiomeric excess. The optical purity of the title compounds was established by hydrolysis to the respective free amino acids, followed by chiral derivatization and HPLC analysis.This was presented at the Fifth International Kyoto Conference on new Aspects of Organic Chemistry, Kyoto, Japan, November 11–15, 1991. Abstract #GO-13.     

Do salt bridges stabilize proteins? A continuum electrostatic analysis

The electrostatic contribution to the free energy of folding was calculated for 21 salt bridges in 9 protein X-ray crystal structures using a continuum electrostatic approach with the DELPHI computer-program package. The majority (17) were found to be electrostatically destabilizing; the average free energy change, which is analogous to mutation of salt bridging side chains to hydrophobic isosteres, was calculated to be 3.5 kcal/mol. This is fundamentally different from stability measurements using pKa shifts, which effectively measure the strength of a salt bridge relative to 1 or more charged hydrogen bonds. The calculated effect was due to a large, unfavorable desolvation contribution that was not fully compensated by favorable interactions within the salt bridge and between salt-bridge partners and other polar and charged groups in the folded protein. Some of the salt bridges were studied in further detail to determine the effect of the choice of values for atomic radii, internal protein dielectric constant, and ionic strength used in the calculations. Increased ionic strength resulted in little or no change in calculated stability for 3 of 4 salt bridges over a range of 0.1-0.9 M. The results suggest that mutation of salt bridges, particularly those that are buried, to "hydrophobic bridges" (that pack at least as well as wild type) can result in proteins with increased stability. Due to the large penalty for burying uncompensated ionizable groups, salt bridges could help to limit the number of low free energy conformations of a molecule or complex and thus play a role in determining specificity (i.e., the uniqueness of a protein fold or protein-ligand binding geometry).     

Latency of cathepsin B secreted by human colon carcinoma cells is not linked to secretion of cystacin C and is relieved by neutrophil elastase

The lysosomal cystein proteinase cathepsin B is shown to be secreted by ten human colon carcinoma cell lines and to accumulate in culture media as a latent enzyme. The cell lines also secrete a physiological inhibitor of cathepsin B, cystatin C. A significant correlation was found between secretion of the latent enzyme and the inhibitor (r = 0.755, P < 0.01). The aim of the present study was to modulate the respective secretion of the two antagonists to test whether or not latency of cathepsin B was due to the concomitant secretion of the inhibitor. SW480 colon carcinoma cells were treated with the acidotropic agent ammonium chloride, phorbol 12-myristate 13-acetate, and the inflammatory cytokines TGF-β, TNF-α, and IL-1β. Ammonium chloride significantly increased latent cathepsin B levels without affecting the constitutive secretion of cystatin C. Phorbol 12-myristate 13-acetate induced a 4- to 5-fold increase in secreted latent cathepsin B, but did not alter significantly the accumulation of cystatin C in media. The cytokines, TGF-β, TNF-α, and IL-1β, had no major effect on the expression of these two antagonists. Latent cathepsin B released from human carcinoma cells could be efficiently activated by neutrophil elastate at neutral pH. It is concluded that latent cathepsin B is a true proenzyme rather than an enzyme-inhibitor comples. In addition, our data from neutrophil elastate activation experiments indicate that a proteolytic system for activation of the tumor cell-secreted latent enzyme may exist in vivo.     

两价盐对C_8－卵磷脂微团溶液液－液相分离的影响

采用激光散射等方法测定了在添加不同的两价无机盐情况下,Ｃ８－卵磷脂微团溶液的液－液相分离曲线,及上变临界温度随盐类型和盐离子强度的变化,并从理论上分析两价盐对Ｃ８－卵磷脂微团溶液吉布斯自由能的影响,推导出－关于盐对该微团溶液相变临界温度影响的半经验半理论公式,可满意地描述该微团溶液的液－液相分离受盐调控的规律。     

Gene disruption in Lactobacillus plantarum strain 80 by site-specific recombination: isolation of a mutant strain deficient in conjugated bile salt hydrolase activity

A chloramphenicol-resistance gene (cml) was introduced into the Lactobacillus plantarum gene encoding conjugated bile acid hydrolasc (cbh) on a ColEl replicon. This plasmid which is nonreplicative in Lactobacillus was used to transform L. plantarum strain 80. A homologous double cross-over recombination event resulted in replacement of the chromosomal cbh gene by the cml-containing cbh gene. The transformants obtained were unable to synthesize active conjugated bile acid hydrolase (Cbh). The Cbh-Cml^R phenotype was stably maintained for more than 100 generations under nonselective conditions.This paper is dedicated with great appreciation to Dr. Frits Berends on the occasion of his retirement as Head of the Biochemistry Department of the TNO Medical Biological Laboratory