Interaction of spermine and DNA

The effect of spermine upon the denaturation temperature (T_m) of DNA's of various base compositions has been found to depend upon both the base composition of the DNA and the pH of the solution. Measurement of the hydrogen ion titration curve of spermine as a function of temperature reveals that the net charge of the spermine molecule is undergoing a rapid change with temperature in the range of temperatures at which DNA denatures. Since the value of T_m depends upon base composition, the correlation of the effect of spermine upon T_m with the base composition of the DNA used may be explainable in terms of the changing degree of ionization of spermine. The binding of spermine to native DNA has also been studied by dialysis equilibrium. There is no significant variation either in the number of strongly binding sites or strength of binding with base composition. It is concluded that there is no evidence of correlation between the binding of spermine and the base composition of DNA.     

Interaction between gamma-carboxyglutamic acid and glutamate dehydrogenase

The amino acid γ-carboxyglutamic acid, recently discovered in some vitamin K-dependent blood-clotting factors, shows interesting kinetic effects on glutamate dehydrogenase. It is not metabolized by the enzyme; it is a powerful competitive inhibitor (K_i = 3.8 × 10^?4 m) with respect to NAD⁺ and glutamate. On the other hand the reverse reaction is activated by γ-carboxyglutamate, both K_m and V being altered; this effect is additive with the well-known activating effect of ADP.     

Interaction between acridine orange and polyriboadenylic acid

The absorption spectra and circular dichroism of aqueous solutions of acridine orange mixed with polY(riboadenylic acid) [poly(rA)] have been measured for different mixing ratios at acid and neutral pH. The binding ratio of dye to poly(rA) has been determined by equilibrium dialysis. At acid pH where poly(rA) is in a double-stranded helix, monomeric dye molecules are intercalated between base pairs, first sparsely and then at neighbouring sites with mutual coupling, as the nucleotide-to-dye mixing ratio decreases. In the presence of excess dye, dimeric dye molecules of antiparallel type are bound to phosphate groups electrostatically and stack together to form linear sequences along a poly(rA) chain. At neutral pH where poly(rA) is single-stranded, isolated intercalation of monomeric dye molecules can occur in the helical parts. At intermediate mixing ratios, half-intercalated dimeric dye molecules are bound to adjacent sites and electronically coupled, inducing characteristic circular dichroism. In the presence of higher amounts of dye, external stacking of dimeric dye molecules of antiparallel type occurs along a poly(rA) chain. The binding of dye cations is suppressed to some degree at acid pH compared to that at neutral pH, owing to the repulsion exerted by protonated adenine bases.     

Interaction between polyuridylic acid and rabbit globin messenger ribonucleic acid

Poly(U) binds to globin mRNA in 0.1m-NaCl. Studies with ribonuclease digestion of this complex suggest that there are polyadenylate-rich sequences in the mRNA containing about 30-40 adenylate residues. The sequences appear to be homogenous and of approximately the same length for both alpha- and beta-globin mRNA. They are most likely located at the 3' terminus of the molecule.     

Calorimetric determination of the heat capacity changes associated with the conformational transitions of polyriboadenylic acid and polyribouridylic acid

The heat capacities of the single-stranded and double-stranded forms of polyadenylic acid, polyuridylic acid, and poly(uridylic and adenylic acid) were determined with a drop heat capacity calorimeter. In addition, the temperature dependence of the apparent partial heat capacity (?Cp) was measured with a newly developed differential scanning calorimeter. The calculated ΔCp at 28°C for the transition poly(A)·poly(A) ? 2 poly(A) was found to be 165 ± 24 cal/Kmol-base pair, compared with a value of 140 ± 28 for the transition poly(A)·poly(U) ? poly(A) + poly(U). The temperature dependence of ?Cp of single-stranded poly(U) was consistent with the conclusion that it is totally unstacked at temperatures above 15°C. The temperature dependence of ?Cp of single-stranded poly(A) was used to determine the base-stacking parameters for poly(A). The experimental results are consistent with a stacking enthalpy change of ?8.5 ± 0.1 kcal/mol bases and a cooperativity parameter σ of 0.57 ± 0.03 for the stacking of adenine bases. These results demonstrate that the heat capacity of single-stranded polynucleotides is greater than that of the double-stranded forms. This increased heat capacity is mainly the result of the temperature dependence of the base-stacking interactions in the single-stranded form.     

肠道菌群与胆汁酸代谢的互相作用

肠道菌群是胃肠道的多种共生细菌和其他微生物的统称,是一个复杂而动态的微生物生态系统,有数十万亿个微生物.胆汁酸是胆汁的主要成分,由肝脏中的胆固醇合成并释放到肠道中以帮助消化吸收膳食脂肪.肠道菌群在胆汁酸代谢中发挥着重要作用,它借助胆盐水解酶和类固醇脱氢酶等通过脱氢、脱羟基和脱硫等作用改变胆汁酸池的组成;随后通过影响胆汁...     

Interaction of spermine with polyphosphoinositides containing liposomes and myo-inositol 1,4,5 triphosphate

The interaction of spermine with liposomes containing 2% phosphatidylinositol, phosphatidylinositol 4 phosphate and phosphatidylinositol 4,5 biphosphate was inferred from the ability of these liposomes to interfere with spermine binding to the resin heparin-Sepharose. The inositol phospholipids tested showed different affinities for spermine: the order of binding strength appear to be phosphatidylinositol phosphatidylinositol 4 phosphate phosphatidylinositol 4,5 biphosphate. The ability of vesicles containing 2% polyphosphoinositides to interact with spermine is comparable to that of either single stranded RNAs or highly negatively charged liposomes. Myo-inositol 1,4,5 triphosphate has a much lower ability to bind spermine.     

稻瘟菌CYP51蛋白F螺旋区保守氨基酸残基与

【目的】研究稻瘟菌CYP51蛋白F螺旋区保守氨基酸残基与烯唑醇的相互作用机制,为稻瘟病菌新型高效特异杀菌剂的开发提供理论依据。【方法】设计稻瘟菌CYP51蛋白F螺旋区保守氨基酸残基突变体P222C、P222H、I223A、I223W、N224A、N224S,截去N端跨膜区36个氨基酸后,在大肠杆菌BL21(DE3) Rosetta菌株中过量表达,采用结合光谱法分析诱导蛋白对烯唑醇的结合能力。【结果】表达的目标蛋白均保持了对药物的结合能力,呈现出II型的结合光谱曲线。相对于野生型蛋白,突变体I223W和I223A对烯唑醇的结合常数Kd值基本不变,N224S、N224A、P222C的Kd值都略有增大,无显著性差异(P>0.05),但是,P222H的Kd值有了显著的增大(P<0.05),表明突变体P222H对烯唑醇的亲和能力显著降低。【结论】稻瘟菌CYP51 P222位点的疏水性与药物结合密切相关。     

Distribution of spermine in bacilli and lactic acid bacteria

Obligate moderately thermophilic bacilli and obligate moderately thermoacidophilic bacilli contained spermine as the major polyamine in addition to putrescine and spermidine. The identity of spermine was confirmed by thin-layer chromatography and high-performance liquid chromatography before and after treatment with putrescine oxidase. Using these methods, thermospermine and spermine can be separated; thermospermine was not present in these organisms. On the other hand, various facultative thermophiles and mesophilic strains of the genus Bacillus, including alkalophiles and halophiles, lack spermine and other tetraamines. No spermine was detected in several strains of mesophilic or facultative slightly thermophilic lactic acid bacteria, Lactobacillus and Streptococcus.     

Interaction between D-amino acid oxidase and small molecules.

1. From the standpoint of monomer-dimer equilibrium of hog kidney D-amino acid oxidase [EC 1.4.3.3] and the interaction between the enzyme and small molecules, the effect of pH on the binding of p-aminobenzoate to the monomer and dimer of the enzyme was studied by kinetic methods and spectrophotometric titration. 2. The maximum binding number of p-aminobenzoate to the dimer is two molecules, and there is no interaction between the two active sites of the dimer (i.e., no cooperativity) over the range of pH from 6.5 to 10. 3. The affinity of the dimer for p-aminobenzoate is several times higher than that of the monomer at pH 6.5-10, and consequently p-aminobenzoate induces dimerization in the equilibrium state of D-amino acid oxidase. The interaction energy of two subunits of the dimer is stabilized by the binding of p-aminobenzoate by 1-2 kcal/mole over the pH range studied. 4. The binding sites of the quasi-substrate, p-aminobenzoate, in the dimer and the intersubunit binding site of the dimer are clearly different, because p-aminobenzoate induces dimerization of the enzyme. 5. The pK values of ionizing groups in the free monomer and the free dimer which participate in the binding of the competitive inhibitor, p-aminobenzoate, are approximately the same, 8.7, as determined from the pH dependence of the affinity of the inhibitor for the enzyme. Furthermore, no pK for the enzyme-inhibitor complex in the pH range 6.5-10 was observed. 6. There is no interaction between the two ionizing groups of the dimer during protonation-deprotonation, because a theoretical equation involving no cooperativity between the two ionizing groups in the dimer explains the results well.