Fullerene-based amino acids and peptides.

Recent advances in the chemistry of fullerene have allowed the synthesis of many classes of novel fullerene derivatives. Among these classes, fullerene-based amino acids and peptides are particularly interesting, both for structural studies and biological applications. In this review, we will discuss our own achievements in this rapidly growing field. In particular, the application of fulleroproline (Fpr) amino acids and peptides to medicinal chemistry and material science will be highlighted.     

Modeling amino acid replacement.

The estimation of amino acid replacement frequencies during molecular evolution is crucial for many applications in sequence analysis. Score matrices for database search programs or phylogenetic analysis rely on such models of protein evolution. Pioneering work was done by Dayhoff et al. (1978) who formulated a Markov model of evolution and derived the famous PAM score matrices. Her estimation procedure for amino acid exchange frequencies is restricted to pairs of proteins that have a constant and small degree of divergence. Here we present an improved estimator, called the resolvent method, that is not subject to these limitations. This extension of Dayhoff's approach enables us to estimate an amino acid substitution model from alignments of varying degree of divergence. Extensive simulations show the capability of the new estimator to recover accurately the exchange frequencies among amino acids. Based on the SYSTERS database of aligned protein families (Krause and Vingron, 1998) we recompute a series of score matrices.     

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.     

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.     

E.s.r. of spin-trapped radicals in gamma-irradiated polycrystalline amino acids, N-acetyl amino acids and dipeptides

The radicals produced in several polycrystalline amino acids, N-acetyl amino acids and dipeptides by gamma-radiolysis at room temperature were investigated by spin-trapping. After irradiation in the solid state, the samples were dissolved in aqueous solutions f t-nitrosobutane and the trapped radicals identified by e.s.r. For alpha-amino acids, deamination radicals were found, and in some cases H-abstraction radicals were also observed. No decarboxylation radicals could be detected. For N-acetyl amino acids, except for N-acetylglycine, the major radical was the decarboxylation radical. For N-acetyglycine the H-abstraction radical from the glycine residue was observed. For dipeptides of the x-glycine, the radical formed by removal of H from the alpha-carbon of the carboxyl-terminal residue was always spin-trapped. Some primary deamination radicals and minor amounts of decarboxylation radicals could also be observed. For dipeptides of the type x-alanine, glycine-x and alanine-x, the decarboxylation radical was always the major spin-trapped radical. Some primary and secondary deamination radicals were also detected.     

Chicken glucagon. Isolation and amino acid sequence studies.

Glucagon was isolated from a side fraction generated during the preparation of insulin and the new pancreatic peptide, avian pancreatic polypeptide from chicken pancreas. The immunological and biological properties are similar to those of beef-pork glucagon. The amino acid composition of chicken glucagon indicates that it contains 1 more serine residue than the porcine hormone and 1 less aspartic acid (asparagine) residue. Thus, chicken glucagon appears to be identical with turkey glucagon.     

Determination of amino sugars and amino acids in glycoconjugates using precolumn derivatization with o-phthalaldehyde.

This report examines the RP-HPLC separation of o-phthalaldehyde derivatives of amino acids, amino sugars, and amino sugar alcohols using either 2-mercaptoethanol or 3-mercaptopropionic acid. A method with pmol sensitivity for the analysis of N-acetylamino sugars of glycoconjugates was elaborated. Upon hydrolysis, amino sugars are reduced with borohydride. Automated precolumn derivatization and chromatographic conditions for the resulting hexosaminitols are the same as those used for the analysis of amino acids. The method has been tested with as little as 2 micrograms of bovine fetuin, with a glycopeptide from bromelain and with an oligosaccharide after periodate oxidation.     

Oxidation products of amino acids and collagen.

Amino acids are known to react with oxidizing agents and some of the degradation products are less complex amino acids. In this study, 14 amino acids as well as fibrous corium collagen and epoxy resin-tanned collagen were reacted with a hydrogen peroxide or hydrogen peroxide-copper sulfate solution, and a number of amino acids were identified chromatographically which were not originally present. These results may explain the presence of several ninhydrin-reactive unknowns formed during hydrolysis of the product obtained by tanning fibrous corium collagen with an epoxy resin.     

Semisynthesis and cytotoxicity of amino acetogenins and derivatives.

Semisynthetic derivatives were prepared from two natural annonaceous acetogenins, rolliniastatin-1 and squamocin, and their cytotoxicity was evaluated. Amino derivatives show decreased bioactivity. Isorolliniastatin-1 was found to be much less toxic than rolliniastatin-1 after intraperitoneal administration to mice, although the in vitro cytotoxicity of both compounds was comparable.     

氨基酸-山梨醇输液的研制

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Acid-labile amino acid precursors in the Murchison meteorite. II: A search for peptides and amino acyl amides.

The basic fraction of the acid-labile amino acid precursors found in hot water extracts of the Murchison meteorite was treated with ninhydrin under conditions that give destruction of free amino acids but allow nearly complete recovery to peptides and amino acylamides. After this treatment and a subsequent acid hydrolysis, the amount of amino acids found corresponded to less than 30 per cent of the precursor content of the basic fraction. Since only 30 percent of the total extract precursors are found in the basic fraction, these results indicate that such compounds, if present, account for no more than 9 mole per cent of the total acid-labile amino acid precursors of the meteorite hot water extract.     

Accumulation of amino acids by lysosomes incubated with amino acid methyl esters.

Rat liver lysosomal preparations incubated with 10(-5) M L-[4,5-3H]leucine methyl ester hydrolyzed the methyl ester and accumulated radioactivity within a particulate compartment. The acculated radioactivity was identified as free leucine by thin layer chromatography. Free leucine was not itself taken up by the lysosomal preparations. The capacity to accumulate leucine was identified as a specific property of lysosomes and was thought to result from the trapping of the free amino acid within the lysosome following the hydrolysis of the methyl ester. Lysosomes also accumulated phenylalanine, serine, and alanine when incubated with the corresponding methyl esters. Leucine accumulation was inhibited by submillimolar concentrations of chloroquine, by the protease inhibitor L-1-tosylamido-2-phenylethyl chloromethyl ketone, and by lowering the pH below 7.0. Efflux of leucine from the lysosomes was highly temperature dependent (activation energy 33 kcal/mol). No evidence was found to suggest that leucine efflux was a carrier-mediated process. The results provide a new methodology for the study of amino acid movements across lysosomal membranes.