Evaluation of the immunocytochemical method for amino acids

Free amino acids can be coupled to proteins by glutaraldehyde. Rabbits immunised with a bovine serum albumin-glutaraldehyde-amino acid conjugate form antibodies that recognise similar conjugates with brain proteins in glutaraldehyde-fixed tissue. Antisera raised against conjugated GABA (gamma-aminobutyrate), glutamate, aspartate, taurine, glutamine, or glycine were tested against a variety of small molecular compounds that had been fixed by glutaraldehyde to brain protein and immobilised on cellulose ester filters for processing together with the brain sections. This system permitted closely similar conditions for testing and immunocytochemistry. After removing antibodies against the carrier used for immunisation and against cross reacting amino acid conjugates the antisera showed a high specificity. The specific nature of the antisera was corroborated by solid phase adsorption to the homologous antigens and by inhibition experiments with free amino acids and amino acid-glutaraldehyde fixation complexes. After transection of the striatonigral pathway the ipsilateral substantia nigra was almost depleted of GABA-like immunoreactivity; this observation lends additional support to the selectivity of the GABA antiserum. A semiquantitative relation was established between the concentration of amino acid before fixation in a model system and the subsequent intensity of immunostaining. Similar model experiments suggested that the conjugation of an amino acid to brain protein with glutaraldehyde, and the immunoreactivity of the conjugates, may be significantly inhibited in the presence of high concentrations of other amino compounds.     

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.     

Efficient cell factories for the production of N-methylated amino acids and for methanol-based amino acid production

The growing world needs commodity amino acids such as L-glutamate and L-lysine for use as food and feed, and specialty amino acids for dedicated applications. To meet the supply a paradigm shift regarding their production is required. On the one hand, the use of sustainable and cheap raw materials is necessary to sustain low production cost and decrease detrimental effects of sugar-based feedstock on soil health and food security caused by competing uses of crops in the feed and food industries. On the other hand, the biotechnological methods to produce functionalized amino acids need to be developed further, and titres enhanced to become competitive with chemical synthesis methods. In the current review, we present successful strain mutagenesis and rational metabolic engineering examples leading to the construction of recombinant bacterial strains for the production of amino acids such as L-glutamate, L-lysine, L-threonine and their derivatives from methanol as sole carbon source. In addition, the fermentative routes for bioproduction of N-methylated amino acids are highlighted, with focus on three strategies: partial transfer of methylamine catabolism, S-adenosyl-L-methionine dependent alkylation and reductive methylamination of 2-oxoacids.     

Phosphoryl amino acids: Common origin for nucleic acids and protein

A series of compounds (DAP-AA) composed of an amino acid (AA) and a dialkyl phosphoryl group (DAP) is the basic elements of life chemistry. Self-catalysis of DAP-AA gives the self-assembly oligopeptides, even in aqueous medium at 38°C. The oligo-nucleotides could also be assembled from nucleosides' phosphorylation by DAP-AA. DAP-AA acts as the energy source as well as the phosphoryl donor for the synthesis of nuclic Acids and protein. A general expression for the self assembly system is proposed.     

GCN2 whets the appetite for amino acids

In response to amino acid starvation, the kinase GCN2 in yeast activates amino acid biosynthesis. Two recent studies (Maurin et al., 2005; Hao et al., 2005) reveal that GCN2 in the brain of mice restricts intake of diets lacking essential amino acids.     

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.     

Classification of essential amino acids for the weanling pig

Feeding experiments with mixtures of purified amino acids show that arginine, leucine, phenylalanine, and valine are required for good growth of weanling pigs. The pig resembles the rat in its ability to synthesize part, but not all of the arginine required. It is now possible to tentatively classify the known amino acids with respect to major growth effects in weanling pigs. The amino acids which must be present in the diet for good growth are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The remaining amino acids may be tentatively classed as dispensable.     

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.     

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.     

Polycondensation of thermal precursors of amino acids and characterization of constituent amino acids.

As a model reaction of polyamino acid formation from non-amino acid precursors, diammonium citraconate (I), ammonium citraconamate(II) and ammonium itaconamate(III) were converted to polyimide type polymers by thermal polycondensation by heating at 130–210°C. The imide type polymer was partially hydrolyzed to the corresponding peptide type polyamino acid. The polymer was composed of α-methylaspartic acid (IV), threo- and erythro-ß-methylaspartic acid (V) and α-(aminomethyl) succinic acid (VI). On the other hand, IV was thermally polycondensed to the corresponding polymer. It was found that the amino acid composition of the polymer was similar to that of the polymer prepared from I, II and III. The formation and isomerization of amino acids during the thermal polycondensation are described.