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1.
d-Aspartate in Human Brain 总被引:3,自引:3,他引:0
Eugene H. Man George H. Fisher Iris L. Payan Rodolfo Cadilla-Perezrios Nancy M. Garcia Radhika Chemburkar Georgine Arends William H. Frey II 《Journal of neurochemistry》1987,48(2):510-515
The presence of the biologically uncommon D-aspartic acid (D-aspartate) in human brain white matter has been previously reported. The earlier study has now been expanded to include D/L-aspartate ratios from 67 normal brains. The data show that the D-aspartate content increases rapidly from 1 year to approximately 35 years of age, levels off in middle age, and then appears to decrease somewhat. The D-aspartate content in gray matter remains at a consistently low level (half of that found in white matter) throughout the human life span. Within the limitations of current analytical methods, there was no detectable difference in D/L-aspartate ratios in white and gray matter of brains with Alzheimer's disease and several other pathologies when compared with brains of normal subjects. However, the presence of a significant D-aspartate level in white matter during the adult life span may lead to changes in protein configuration related to dysfunctions associated with the aging brain. 相似文献
2.
The reaction of racemization in which the L amino acids are reversibly converted into the corresponding D amino acids, proceeds in geological environment at such a slow rate that it may be used as a geochronometer. However, in fossils several parameters may affect the rate of racemization, i.e. moisture, surface, pH buffer and metal cations. This work consists of a systematic study of total amino acid content in fossil bones from two neanderthalian sites. The amino acid distributions of all specimens were determined and compared to that of fresh bone. The D/L amino acid were quantified and expressed in terms of age as a function of the temperature. The results led us to consider the «La Roquette» site older than «Les Canalettes» site. 相似文献
3.
Summary We have found that guanidine acetate catalyses the transformation of a -benzyl-aspartyl peptide (Boc-Asp-(OBzl)-Leu-Trp-OMe) to an aminosuccinyl peptide (Boc-Asu-Leu-Trp-OMe). The reaction was accompanied by partial epimerization. However, not even a small amount of epimerization could be detected when the aminosuccinyl peptide was synthesised from Boc-Asp-Leu-Trp-OMe with the addition of DIC, HOPfp and guanidine acetate (as a catalyst). This reaction seems to be suitable for the epimerization-free solid phase synthesis of aminosuccinyl peptides, e.g. Asu6-Lamprey-III-GnRH (Glp-His-Trp-Ser-His-Asu-Trp-Lys-Pro-Gly-NH2). 相似文献
4.
Summary. The influence of the operation conditions (temperature and residence time) of a thermic treatment on the total amount (free
and protein-bound) of amino acid enantiomers of dry fullfat soya was investigated. Total amino acid content was determined
using conventional ion-exchange amino acid analysis of total hydrolysates and chiral amino acid analysis was performed by
HPLC after precolumn derivatization with o-phthaldialdehyde and 1-thio-β-D-glucose tetraacetate. Contrary to corn that was investigated previously, notable racemization
was detected even at lower temperatures. At 140 °C the ratio of the D-enantiomer was 0.87% for glutamic acid, 2.81% for serine,
and 1.92% for phenylalanine; at 220 °C the ratios of the D-enantiomer of the above amino acids were 1.43, 4.61, and 4.68%,
respectively. The concentration of several L-amino acids decreased. At 220 °C there was 10% less L-glutamic acid, 17% less
L-serine, 5% less L-phenylalanine, 6.6% less L-aspartic, acid and 21% less L-lysine than in the control; their loss can be
assigned to different degrees of L – D conversion. While nearly complete transformation of L-phenylalanine can be attributed
to racemization, the main cause of the loss of L-lysine is not racemization. The treatments in the same order of magnitude
resulted in the formation of more D-amino acids and greater extent of racemization of amino acids in fullfat soya than that
of maize.
Authors’ address: J. Csapó, Faculty of Animal Science, Institute of Chemistry, University of Kaposvár, Guba S. u. 40., H-7400
Kaposvár, Hungary 相似文献
5.
Marian Goriup Ulrike T. Strauss Ulfried Felfer Wolfgang Kroutil Kurt Faber 《Journal of Molecular Catalysis .B, Enzymatic》2001,15(4-6)
Enzymatic racemization of mandelic acid derivatives modified at the α-hydroxy acid moiety was achieved using mandelate racemase [EC 5.1.2.2]. Whereas α-amino acid derivatives, such as phenyl glycine and mandelic acid hydrazide were not accepted, the mandelic acid amide was racemized at an acceptable rate. The latter was significantly enhanced by an electron-withdrawing substituent in the phenyl moiety. Based on the catalytic mechanism of the enzyme, the relative activities of non-natural substrates could be explained by steric and electronic reasons. 相似文献
6.
The preferred mechanisms of racemization for three tris chelate complexes, Co(acac)3, Fe(phen)3 3+ and Fe[S2CN(CH2)4]3, were investigated by molecular modeling. The transition states for both a Bailar twist and a Rây-Dutt twist were considered; semi-empirical calculations (PM3) yielded activation energies. The preferred mechanism was the Bailar twist for Co(acac)3 and Fe[S2CN(CH2)4]3 with activation energies of 83.2 and 7.3 kcal mol−1, respectively, and the Rây-Dutt twist for Fe(phen)3 3+ with an activation energy of 114.4 kcal mol−1. These results are compared with those of geometrical models. 相似文献
7.
A two-step process to synthesize racemic lorcaserin was developed from 2-(4-chlorophenyl)ethanol via formation of bromide or tosylate derivatives. These derivatives were reacted with allylamine in neat conditions to provide pure N-(4-chlorophenethyl)allylammonium chloride. This compound was cyclized in neat conditions using aluminum or zinc chloride to give racemic lorcaserin. After resolution of enantiomers, the wrong enantiomer was racemized and recycled to give new R-lorcaserin. 相似文献
8.
Circular dichroism (CD) spectra have been measured in the range of 400-200 nm on CH3OH solutions of both enantiomers for the almost complete series of monoaza[5]helicenes, namely the molecules where the hetero N atom occupies positions 1, 3, 4, 5, 6, and 7, respectively (the 2 isomer is missing due to difficulties in the synthesis). CD spectra recorded at controlled room temperature allow one to define precise racemization rates, that are nicely interpreted on the basis of DFT molecular orbital calculations. Time-dependent DFT methods provide us with calculated CD and UV spectra, that are compared with the corresponding experimental data. We discuss the role of the N atom in determining the height of the racemization barrier and in shaping the appearance of the CD spectra. 相似文献
9.
本文试图用北京猿人和山西丁村人所在地层中伴生动物化石内的天门冬氨酸、异亮氨酸外消旋程度推算北京猿人和山西丁村人地点的年龄和山顶洞所经历的平均温度。 相似文献
10.
Nestl BM Voss CV Bodlenner A Ellmer-Schaumberger U Kroutil W Faber K 《Applied microbiology and biotechnology》2007,76(5):1001-1008
Biocatalytic racemization of aliphatic and aryl-aliphatic sec-alcohols and alpha-hydroxyketones (acyloins) was accomplished using whole resting cells of bacteria, fungi, and one yeast. The mild (physiological) reaction conditions ensured the suppression of undesired side reactions, such as elimination or condensation. Cofactor and inhibitor studies suggest that the racemization proceeds through an equilibrium-controlled enzymatic oxidation-reduction sequence via the corresponding ketones or alpha-diketones, respectively, which were detected in various amounts. Ketone formation could be completely suppressed by exclusion of molecular oxygen. Figure Biocatalytic racemization whole microbial cells. 相似文献