Permeability of liposomes towards amino alcohol and amino acid nitroxides

Electron spin resonance (ESR) allowed the analysis of the encapsulation of amino alcohols and amino acids labeled with nitroxide groups into multilamellar liposomes. The stability and permeability of these phospholipid vesicles were studied in terms of time dependance and structure of these biomolecules.     

Transformation of some hydroxy amino acids to other amino acids

It has been observed that -hydroxy--amino acids are transformed into other amino acids, when heated in dilute solutions with phosphorous acid, phosphoric acid or their ammonium salts. It has been shown that as in the case of previously reported glycine-aldehyde reactions, glycine also reacts with acetone to give -hydroxyvaline under prebiologically feasible conditions. It is suggested, therefore, that the formation of -hydroxy--amino acids and their transformation to other amino acids may have been a pathway for the synthesis of amino acids under primitive earth conditions.     

Transformation of some hydroxy amino acids to other amino acids.

It has been observed that beta-hydroxy-alpha-amino acids are transformed into other amino acids, when heated in dilute solutions with phosphorous acid, phosphoric acid or their ammonium salts. It has been shown that as in the case of previously reported glycine-aldehyde reactions, glycine also reacts with acetone to give beta-hydroxyvaline under prebiologically feasible conditions. It is suggested, therefore, that the formation of beta-hydroxy-alpha-amino acids and their transformation to other amino acids may have been a pathway for the synthesis of amino acids under primitive earth conditions.     

Formation of specific amino acid sequences during thermal polymerization of amino acids

The mechanism of the thermal polymerization (at 180°C) of glutamic acid, tyrosine, and glycine has been studied. Glutamic acid is quickly and almost completely converted into pyroglutamic acid. The only dipeptide that is formed by dimerization of the remaining two amino acids is cyclic glycyl-tyrosine (a diketopiperazin). In a secondary reaction pyroglutamic acid interacts with cyclic glycyl-tyrosine and yields pyroglutamyl-glycyltyrosine and pyroglutamyl-tyrosyl-glycine. Other di- or tripeptides are not observed. The preferential appearance of the two pyroglutamyl-peptides has been reported earlier by Nakashima et al. (1977). The present data explain those results. Model experiments show that cyclic glycyl-tyrosine can also be cleaved by other acids or bases. In the presence of acetic acid at 118°C N-acetyl-glycyl-tyrosine is the major product. Partial hydrolysis predominantly yields tyrosyl-glycine. These effects are explained by stereospecific interactions. The results on self-ordering of amino acids during peptide formation are discussed in respect of the origin of prebiotic enzymes and genetic information.     

Solubilities of amino acids

The Mettler/Paar precision density meter DMA-02D has been used to determine the concentration of saturated solutions of amino acids at 20.0, 25.0, and 29.8 °C. The technique has proven itself an elegant and precise method. The solubilities of all of the amino acids with the exceptions of proline, lysine, and cystine have been measured. The Gibbs free energies of transfer from saturated water solution to 1M Na₂SO₄ and to 1M Gu·HCL along with the van't Hoff heats and entropies have been calculated. The van't Hoff heats have been compared with the calorimetrically determined heats for some of the amino acids. The Lumry-Rajender relation between the entropy and heats has been observed. The process of transfer of the amino acids from water to the solvents is primarily enthalpic rather than entropic.     

Lipophilicity of amino acids

Summary The lipophilicity (or hydrophobicity) of amino acids is an important property relevant for protein folding and therefore of great interest in protein engineering. For peptides or peptidomimetics of potential therapeutic interest, lipophilicity is related to absorption and distribution, and thus indirectly relates to their bioactivity. A rationalization of peptide lipophilicity requires basic knowledge of the lipophilicity of the constituting amino acids. In the present contribution we will review methods to measure or calculate the lipophilicities of amino acids, including unusual amino acids, and we will make a comparison between various lipophilicity scales.     

Micro-analysis of amino acids

An automated amino acid analyzer has been developed for the analysis of amino acids with the sensitivity at the 10–100 pmol level except for proline which requires >50 pmol. o-Phthalaldehyde, in the presence of 2-mercaptoethanol, is used for the fluorometric detection of amino groups (Roth, M. (1971) Anal. Chem. 43, 880–882). A post-column reaction of the amino acid with sodium hypochlorite (Bohlen, P. and Mellet, M. (1979) Anal. Biochem. 94, 313–321) gives oxidation products amenable to detection with o-phthalaldehyde. The instrument uses high-performance liquid chromatographic pumps capable of micro-flow rates with a minimum pulsation. The method is suitable for routine analyses of amino acids at picomole levels with reproducibility and accuracy comparable to the ninhydrin-based amino acid analysis.     

Effect of natural amino alcohols on the yield of essential amino acids and the amino acid pattern in stressed barley

Summary By application with 2-aminoethanol (2-AE) and choline chloride (CC) in pot experiments the effect of drought stress on barley plants was diminished. In treated plants an increase of the grain yield by 14% (2-AE) and 40% (CC) and a decrease of the stress metabolites glycine betaine and trigonelline was observed. Additionally, treated barley plants showed higher yields of essential amino acids as well. The contents of proline (stress indicator) and arginine (precursor of the stress metabolite putrescine) of treated plants were by 12% and 22% respectively, lower than in untreated plants.     

Effect of dietary amino acid on the amino acid pool of Aedes aegypti

Ion-exchange chromatography analysis of whole body extracts of Aedes aegypti mosquitoes which had received amino acids in their diet revealed that generally there were changes in the titre of two or more amino acids. Cysteine produced the greatest number of changes and was toxic to the insect. Of the ten amino acids provided, none resulted in the significant change in the concentration of tyrosine following a blood meal as was observed in previous studies. Evidence is presented for the conversion of arginine to ornithine and for the synthesis of arginine from glutamic acid. The data presented tend to support the hypothesis of lysine synthesis from α-ketoglutarate and for the use of proline as an energy reserve in the insect.