High-resolution nuclear magnetic resonance spectra of selectively deuterated staphylococcal nuclease

An analog of staphylococcal nuclease has been prepared in which all amino acids, except the six following, are fully deuterated: tryptophan; methionine; tyrosine, in ring positions 2 and 6; histidine, in ring position 2; aspartic acid and asparagine, beta-methylene; and glutamic acid and glutamine, gamma-methylene. The analog has a much simpler high-resolution nuclear magnetic resonance spectrum than the fully protonated enzyme. The effects of calcium ion and of the inhibitor 3', 5'-thymidine diphosphate on the spectrum of the analog were readily detected.     

Structural insight into the transglycosylation step of bacterial cell-wall biosynthesis

Peptidoglycan glycosyltransferases (GTs) catalyze the polymerization step of cell-wall biosynthesis, are membrane-bound, and are highly conserved across all bacteria. Long considered the "holy grail" of antibiotic research, they represent an essential and easily accessible drug target for antibiotic-resistant bacteria, including methicillin-resistant Staphylococcus aureus. We have determined the 2.8 angstrom structure of a bifunctional cell-wall cross-linking enzyme, including its transpeptidase and GT domains, both unliganded and complexed with the substrate analog moenomycin. The peptidoglycan GTs adopt a fold distinct from those of other GT classes. The structures give insight into critical features of the catalytic mechanism and key interactions required for enzyme inhibition.     

Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination

Chlorinated natural products include vancomycin and cryptophycin A. Their biosynthesis involves regioselective chlorination by flavin-dependent halogenases. We report the structural characterization of tryptophan 7-halogenase (PrnA), which regioselectively chlorinates tryptophan. Tryptophan and flavin adenine dinucleotide (FAD) are separated by a 10 angstrom-long tunnel and bound by distinct enzyme modules. The FAD module is conserved in halogenases and is related to flavin-dependent monooxygenases. On the basis of biochemical studies, crystal structures, and by analogy with monooxygenases, we predict that FADH2 reacts with O2 to make peroxyflavin, which is decomposed by Cl-. The resulting HOCl is guided through the tunnel to tryptophan, where it is activated to participate in electrophilic aromatic substitution.     

Correlation between location and time of expression for genes in a single operon

When the histidine Operon in Salmonella typhimurium becomes derepressed in the presence of 4-amino-5-imidazole carboxamide ribonucleoside, derepression of the enzymes for histidine biosynthesis Occurs in a temporal sequence which corresponds with the positional sequence of the genes in the histidine Operon, approximately 20 minutes intervening between the derepression of the first and that of the last enzyme studied. In the case of the deletion mutant, hisH,B22, the interval between the derepression of the first and that of the last enzyme was reduced from 20 minutes to 10 minutes. This reduction was due exclusively to the fact that the interval between the derepressions of the two enzymes, the structural genes for which are located on either side of the deletion, was almost completely eliminated. The results support the genetic evidence for the physical absence of genetic material situated between these two genes.     

Tryptophan deficiency in rabbit reticulocytes: polyribosomes during interrupted growth of hemoglobin chains

Of several amino acids essential for optimum hemoglobin synthesis by the rabbit reticulocyte, only omission of tryptophan results in polyribosome disaggregation. This disaggregation is prevented by the omission of both tryptophan and an amino acid that is relatively more essential than tryptophan for hemoglobin synthesis. Since tryptophan is located only near the amino-terminal ends of both chains of rabbit globin, the results indicate that single ribosomes and those in polyribosomes are in a dynamic state in the intact cell.     

不同氨基酸对At.f菌生长情况的影响

通过在不同pH条件下培养At.f菌,并监测其生长情况,以确定At.f菌生长的最适pH,再向所确定的最适pH的9K培养基中添加不同氨基酸,研究不同氨基酸对At.f菌生长情况的影响。结果表明：pH为2.0的培养基中菌种的生长情况最好;另外丙氨酸、缬氨酸、亮氨酸、异亮氨酸、甲硫氨酸、苯丙氨酸、色氨酸、脯氨酸、酪氨酸、甘氨酸、半胱氨酸对Fe^2＋的利用率较高,而丝氨酸、天冬酰胺、谷氨酰胺、组氨酸作用结果则相反。从而得出结论：At.f菌生长的最适pH为2.0;非极性氨基酸、成环氨基酸对At.f菌生长有促进作用,丝氨酸、天冬酰胺、谷氨酰胺、组氨酸对At.f菌生长有抑制作用。     

Melanocyte-stimulating hormone: activity in thermal polymers of alpha-amino acids

Thermal polymers of arginine, glutamic acid, glycine, histidine, phenylalanine, and tryptophan have melanocyte-stimulating activity. The fact that similar polymers lack such activity indicates that the effect is related to the specific amino acid residues. The active polymers are discussed as a model of an evolutionary precursor of contemporary melanocyte-stimulating hormone.     

菏泽鸡皮山药中氨基酸含量的测定

[目的]测定菏泽鸡皮山药中的氨基酸含量,为菏泽鸡皮山药的资源开发提供科学数据。[方法]鸡皮山药采自山东省菏泽市城郊农村,长根状,直径1.6~2.9 cm,样品经酸解处理后用氨基酸分析仪测定其氨基酸组成。[结果]菏泽鸡皮山药中含有19种氨基酸,种类齐全,总量达19225.1 mg/kg;其中含有8种人体必需氨基酸,分别为苯丙氨酸、蛋氨酸、赖氨酸、亮氨酸、色氨酸、苏氨酸、缬氨酸和异亮氨酸,总量为6763.0 mg,占总氨基酸含量的35.18%;还含有婴儿必需氨基酸精氨酸与组氨酸,含量为3688.5 mg,占氨基酸总量的19.19%。[结论]菏泽鸡皮山药中必需氨基酸总量所占比例较高,在医学和营养学上具有很高的研究价值。     

Tryptophan operon of Escherichia coli: regulatory behavior in Salmonella typhimurium cytoplasm

Hybrids hemizygous for the tryptophan genes were prepared by episomal transfer of an Escherichia coli element into Salmonella typhimurium. Regulation of enzyme production by hybrids carrying wild-type E. coli genes in response to changes in the growth medium occurs in precisely the same manner as in haploid E. coli wild type. Mutant alleles of the anthranilate synhetase gene of E. coli which prevent derepression in E. coli function identically in S. typhimurium. At least one Salmonella tryptophan regulatory gene unlinked to the structural genes is known. Any dijferences which may exist between the tryptophan regulatory genes of E. coli and Salmonella have little effect on the regulation of enzyme formation in hybrids.     

色氨酸对拟南芥酪氨酸降解途径缺陷突变体sscd1细胞死亡的影响

为了解色氨酸处理是否影响sscd1的细胞死亡,以拟南芥野生型Columbia(Col–0)和sscd1突变体为试验材料,用色氨酸处理,观察并统计幼苗的死亡情况,检测叶绿素含量,分析酪氨酸降解途径基因HGO、MAAI和SSCD1以及活性氧诱导基因BAP1、OXI1、ZP的表达。结果表明：色氨酸处理能明显抑制sscd1突变体幼苗死亡,增加叶绿素的合成,抑制sscd1突变体中酪氨酸降解途径基因HGO和MAAI以及活性氧诱导基因BAP1、OXI1、ZP的上调。推测色氨酸可能通过增加叶绿素的生物合成,减少活性氧的产生来抑制酪氨酸降解途径突变体sscd1的细胞死亡。     

Erythropoietin: hypothesis of action tested by analog computer

The action of erythropoietin on the pool of undifferentiated bone marrow cells has been examined with the aid of a model tested with an analog computer. The model is consistent with reported experimental results. The essential aspects of the action are (i) the effect is exerted during the S phase of the cell's cycle; (ii) " effective " erythropoietin is present in the cell only during G(1) and part of S; and, (iii) hormone molecules survive in the cell for only a limited time in effective form and require a certain time to assume this form.     

Circadian rhythm for tryptophan pyrrolase activity and its circulating substrate

Hepatic tryptophan pyrrolase and its circulating substrate, whole blood tryptophan, have a circadian rhythmicity in mice. Intact adrenocortical function is required for the normal rhythmicity of both enzyme and substrate although an altered but less apparent rhythm persists in the adrenalectomized state.     

Synthetic polypeptide antagonists of the hypothalamic luteinizing hormone releasing factor

Two analogs of the hypothalamic luteinizing hormone releasing factor modified at the histidine-2 position were tested for biological activity (secretion of luteinizing hormone) in cultures of dispersed rat anterior pituitary cells. The analog in which glycine was substituted for histidine at position 2, [Gly(2)]LRF, behaves as a partial agonist releasing less than 50 percent of the luteinizing hormone secreted at maximum concentrations of the releasing factor, while the analog in which histidine at position 2 is deleted has no significant agonist activity at any of the doses tested. When added to the cultured cells at molar ratios 10(3) to 10(4) times that of the luteinizing hormone releasing factor, both analogs decrease the amount of luteinizing hormone secreted in response to the releasing factor.     

Genetic and pharmacological suppression of oncogenic mutations in ras genes of yeast and humans

The activity of an oncoprotein and the secretion of a pheromone can be affected by an unusual protein modification. Specifically, posttranslational modification of yeast a-factor and Ras protein requires an intermediate of the cholesterol biosynthetic pathway. This modification is apparently essential for biological activity. Studies of yeast mutants blocked in sterol biosynthesis demonstrated that the membrane association and biological activation of the yeast Ras2 protein require mevalonate, a precursor of sterols and other isoprenes such as farnesyl pyrophosphate. Furthermore, drugs that inhibit mevalonate biosynthesis blocked the in vivo action of oncogenic derivatives of human Ras protein in the Xenopus oocyte assay. The same drugs and mutations also prevented the posttranslational processing and secretion of yeast a-factor, a peptide that is farnesylated. Thus, the mevalonate requirement for Ras activation may indicate that attachment of a mevalonate-derived (isoprenoid) moiety to Ras proteins is necessary for membrane association and biological function. These observations establish a connection between the cholesterol biosynthetic pathway and transformation by the ras oncogene and offer a novel pharmacological approach to investigating, and possibly controlling, ras-mediated malignant transformations.     

离体条件下辽细辛精油对灰葡萄孢菌细胞壁降解酶活性的影响

以辽细辛精油为材料,以黄瓜灰霉病致病菌灰葡萄孢菌为靶标,利用紫外可见分光光度计,采用比色法在离体条件下测定了辽细辛精油对灰葡萄孢菌细胞壁降解酶活性的影响.结果表明:辽细辛精油对果胶甲基半乳糖醛酸酶(pectin methylgalactuionase,PMG)、胞内果胶甲基反式消除酶(pectin methyltrans-eliminase,PMTE)、果胶总酶、胞内1,2-β-D葡聚糖酶(C1酶)、胞外羧甲基纤维素酶(Cx酶)和蛋白酶均主要表现为激活作用;对胞外PMTE酶和胞内C1酶表现为抑制作用;激活/抑制作用与精油浓度之间不成比例关系.这说明辽细辛精油对灰葡萄孢菌细胞壁降解酶活性的影响不是抑菌作用的主要机制.     

Induced phenotypic resistance to an antimetabolite

Resistance to bacteriostasis by 2-thiazole alanine develops rapidly; however, such resistance is lost during growth in the absence of the analog. This induced resistance is accompanied by increased formation of an enzyme sensitive to 2-thiazole alanine. Maintenance of the elevated enzyme levels in growing cells, like resistance, requires the presence of the analog.     

Biosynthesis and Accumulation of Formic Acid in the Poison Gland of the Carpenter Ant Camponotus pennsylvanicus

Formic acid synthesis in the poison gland of Camponotus pennsylvanicus is closely related to the C-1 metabolism of the glandular cells. Serine, glycine, and histidine are potential C-l donors to formic acid by several tetrahydrofolate intermediates. Formic acid is accumulated by its transfer to an insulated reservoir, so that the ant avoids the acid's cytotoxicity. This combination of biochemical and morphological features provides an autodefensive mechanism. Possible factors that regulate the biosynthesis of formic acid in the poison gland apparatus are discussed.     

Tryptophan-Requiring Mutants of the Plant Arabidopsis thaliana

Although amino acid auxotrophs are among the most frequently isolated mutations in microorganisms, no mutants that require amino acids have been isolated at the whole plant level. Tryptophan-requiring mutants of the cruciferous plant Arabidopsis thaliana have now been isolated by selecting for resistance to 5-methylanthranilic acid. The tryptophan requirement of one mutant, trpl-1, results from a defect in the second step of the tryptophan pathway catalyzed by anthranilate phosphoribosyl transferase. Mutant trpl-1 plants are highly fluorescent and aromatic because they accumulate anthranilic acid and anthranilate beta-glucoside. Plants homozygous for the trpl-1 mutation exhibit a syndrome of morphological defects suggestive of a defect in the biosynthesis, metabolism, or localization of a tryptophan derivative such as auxin. All of these morphological phenotypes cosegregate with the tryptophan requirement as a simple Mendelian recessive trait.