Interactions between homopolymeric amino acids (HPAAs)

Many human proteins contain consecutive amino acid repeats, known as homopolymeric amino acid (HPAA) tracts. Some inherited diseases are caused by proteins in which HPAAs are expanded to an excessive length. To this day, nine polyglutamine-related diseases and nine polyalanine-related diseases have been reported, including Huntington's disease and oculopharyngeal muscular dystrophy. In this study, potential HPAA-HPAA interactions were examined by yeast two-hybrid assays using HPAAs of approximately 30 residues in length. The results indicate that hydrophobic HPAAs interact with themselves and with other hydrophobic HPAAs. Previously, we reported that hydrophobic HPAAs formed large aggregates in COS-7 cells. Here, those HPAAs were shown to have significant interactions with each other, suggesting that hydrophobicity plays an important role in aggregation. Among the observed HPAA-HPAA interactions, the Ala28-Ala29 interaction was notable because polyalanine tracts of these lengths have been established to be pathogenic in several polyalanine-related diseases. By testing several constructs of different lengths, we clarified that polyalanine self-interacts at longer lengths (>23 residues) but not at shorter lengths (six to approximately 23 residues) in a yeast two-hybrid assay and a GST pulldown assay. This self-interaction was found to be SDS sensitive in SDS-PAGE and native-PAGE assays. Moreover, the intracellular localization of these long polyalanine tracts was also observed to be disturbed. Our results suggest that long tracts of polyalanine acquire SDS-sensitive self-association properties, which may be a prerequisite event for their abnormal folding. The misfolding of these tracts is thought to be a common molecular aspect underlying the pathogenesis of polyalanine-related diseases.     

Importance of hydrogen-bonding sites in the chiral recognition mechanism between racemic D3 terbium(III) complexes and amino acids

The perturbation of the racemic equilibrium of luminescent D3 terbium(III) complexes with chelidamic acid (CDA), a hydroxylated derivative of 2,6-pyridine-dicarboxylic acid (DPA), by added chiral biomolecules such as L-amino acids has been studied using circularly polarized luminescence and 13C NMR spectroscopy. It is shown in this work that the chiral-induced equilibrium shift of [Tb(CDA)3](6-) by L-amino acids (i.e. L-proline or L-arginine) was largely influenced by the hydrogen-bonding networks formed between the ligand interface of racemic [Tb(CDA)3](6-) and these added chiral agents. The capping of potential hydrogen-bonding sites by acetylation in L-proline led to a approximately 100-fold drop in the induced optical activity of the [Tb(CDA)3](6-):N-acetyl-L-proline system. This result suggested that the hydrogen-bonding networks serve as the basis for further noncovalent discriminatory interactions between racemic [Tb(CDA)3](6-) and added L-amino acids.     

Interaction of cis-Pt(ino)2Cl2 with amino acids

The reactions of cis-Pt(ino)2Cl2 with the amino acids Gly, L-Ala, L-Val, L-Ileu, L-Phe and L-Pro were studied in methanolic solutions. The (1:1) adducts of the formulas cis-[Pt(ino)2(am-ac)]Cl were isolated from these reactions in the solid state, which in turn produce the cis-[Pt(ino)2(am-acH)Cl]Cl complexes, by treating the former with equivalent amounts of HCl, in aqueous solutions. The complexes were characterized with elemental analysis, conductivity measurements, IR, 1H NMR, and 13C NMR spectra. The results show that the purine ring of inosine interacts with the aliphatic side chain of the amino acids. The platination increases the percentage of the C3'-endo-anti conformation of the sugar part of inosine.     

Stereoselective routes towards the synthesis of unusual bis(amino acids) and cyclic amino acids

Stereoselective syntheses are described of bridged bis(glycines) as conformationally constrained substitutes for cystine, and of cyclic -amino acids where the -carbon of the amino acid is part of a five-, six- or seven-membered ring which may hold a hydroxy group as a threonine analogue.     

Stereoselective routes towards the synthesis of unusual bis(amino acids) and cyclic amino acids

Summary Stereoselective syntheses are described of bridged bis(glycines) as conformationally constrained substitutes for cystine, and of cyclic α-amino acids where the α-carbon of the amino acid is part of a five-, six- or seven-membered ring which may hold a hydroxy group as a threonine analogue.     

The reaction of iodobenzene-p-sulphonyl chloride (pipsyl chloride) with certain amino acids and peptides, and with insulin

1. A system of separation using buffered Celite columns is described that enables the pipsyl derivatives of most of the common amino acids to be separated. 2. The reaction of pipsyl chloride with several amino acids not included in previous studies has been investigated. In particular, knowledge of the acid-soluble pipsyl derivatives of arginine, histidine, lysine, tyrosine and cysteic acid has been extended. 3. Reproducible factors have been obtained that enable corrections to be applied for the breakdown of pipsylamino acids on acid hydrolysis. 4. The reaction of pipsyl chloride with peptides has been studied under various conditions. 5. The extent of the reaction between pipsyl chloride and insulin depends on the nature of the solvent–buffer system, and under the best conditions so far found is about 75% complete. 6. In an Appendix, the separation of pipsylamino acids by thin-layer chromatography is described.     

Kinetic study of the reaction between trinitrobenzenesulfonic acid and amino acids with a trinitrobenzenesulfonate ion-selective electrode

Potentiometric studies of the reaction between trinitrobenzenesulfonic acid (TNBS) and several amino acids with the TNBS electrode indicate that the reaction is first-order with respect to TNBS and amino acid concentration. The reaction is zero-order with respect to hydroxide concentration at pH greater than 10.5, indicating that the nonprotonated amino group is the reactive species. Rate constants were calculated for each amino acid and a simple mechanism of the reaction is proposed.     

The Effect of (2-chloroethyl)-trimethylammonium Chloride on the Growth of Barley

Barley (Hordeum vulgare L. C.I.666) was shown to be susceptibleto the growth retardant (2-chloroethyl)-trimethylammonium chloride(CCC). The estimation of cell number in the dwarfed third leafblade indicated that a decrease in mitotic activity had occurredin treated plants. There was also a decrease in cell size intreated plants. The dwarfing action of CCC was reversed by exogenousgibberellic acid (GA₃) but this was shown to be the result ofincreased cell elongation only. GA₃ did not promote cell divisionin healthy or CCC-treated plants. Assay of endogenous gibberellinsshowed a significant reduction in the level of a substance correspondingto GA₃ in CCC-treated plants. It is suggested that CCC-induceddwarfing of barley is largely the result of a reduction in meristematicactivity. This may be related to an effect on gibberellin biosynthesisbut is not reversed by the application of exogenous GA ₃.     

Kinetics and mechanism of the reaction between 1,2-diaminopropanetetra-acetatoferrate(III) and cyanide ion

The present study examines the kinetics and mechanism of the system [FePDTA(OH)]²⁻ + 5CN⁻ ⇌ [Fe(CN)₅OH]³⁻ + PDTA⁴⁻ at pH= 11.0±0.02, I= 0.25 M and temperature = 25 ± 0.1 °C. The reaction has been studied spectrophotometrically at 395 nm (λ_max of [Fe(CN)₅OH]³⁻). The data show that the reaction has three distinguishable stages; the first stage is formation of [Fe(CN)₅OH]³⁻, the second is conversion of [Fe(CN)₅OH)]³⁻ to [Fe(CN)₆]³⁻ and last is reduction of [Fe(CN)₆]³⁻ to [Fe(CN)₆]³⁻ by the released ligand, viz., PDTA. The first reaction shows variable order dependence on cyanide concentration, one at high cyanide concentration and two at low cyanide concentration. The second reaction exhibits first order dependence on the concentration of [Fe(CN)₅OH]³⁻ as well as cyanide. The reverse reaction between [Fe(CN)₅OH]³⁻ and PDTA is first order in [Fe(CN)₅OH]³⁻ and PDTA, and inverse first order in cyanide. On the basis of forward and reverse rate studies, a five-step mechanism has been proposed for the first reaction.