Aspartylalanine

Aqueous solvation of carboxylate groups, as present in the glycine zwitterion and the dipeptide aspartylalanine, is studied employing a force-field that includes distributed multipole electrostatics and induction contributions (Amoebapro: P. Ren and J. W. Ponder, J. Comput. Chem., 2002, 23, 1497; P. Ren and J. W. Ponder, J. Phys. Chem. B, 2003, 107, 5933; J. W. Ponder and D. A. Case, Adv. Protein Chem., 2003, 66, 27). Radial and orientation distribution functions, as well as hydration numbers, are calculated and compared with existing simulation data derived from Car-Parrinello molecular dynamics (CPMD), and also distributed-charge force-fields. Connections are also made with experimental data for solvation of carboxylates in water. Our findings show that Amoebapro yields carboxylate solvation properties in very good agreement with CPMD results, significantly closer agreement than can be obtained from traditional force-fields. We also demonstrate that the influence of solvation on the conformation of the dipeptide is markedly different using Amoebapro compared with the other force-fields.

This work describes further development of our previously presented method for determination of acidic sulfur/phosphor-containing amino acids, gamma-glutamyl di/tripeptides, and beta-aspartyl dipeptides. Automated precolumn fluorogenic derivatization was performed with o-phthaldialdehyde/beta-mercaptoethanol and the derivatives were separated by reversed-phase liquid chromatography. The method was optimized for the analysis of brain tissue extracts. Due to the complex sample matrix, three separation schemes with complementary selectivities were developed. Different extraction protocols were evaluated and sonication of frozen tissue powder in methanol-H2O (9:1, v/v) yielded the highest recoveries and precision. beta-Mercaphtoethanol and EDTA were added to the extraction media to inhibit spontaneous oxidation of thiol-containing amino compounds. Analyte identification was based on retention times and recovery of standards added to extracts. The following compounds were identified in rat cerebral cortex (mean tissue concentration +/- SD, n = 6): gamma-glutamylglutamine (38.5 +/- 12.6 microM), gamma-glutamylglutamate (14.4 +/- 6.0 microM), gamma-glutamyltaurine (4.9 +/- 2.2 microM), beta-aspartylglycine (4.0 +/- 0.4 microM), beta-aspartyltaurine (3.7 +/- 0.6 microM), O-phosphoserine (3.2 +/- 0.8 microM), gamma-glutamylcysteine (1.9 +/- 0.3 microM), gamma-glutamylglycine (1.1 +/- 0.1 microM), and gamma-glutamylcysteateglycine (0.8 +/- 0.1 microM). In addition over 15 unidentified components were found. Cysteate, cysteine sulfinate, homocysteate, homocysteine sulfinate, O-Sulfoserine, gamma-glutamylaspartate, gamma-glutamylcysteate, gamma-glutamylhistidine, and beta-aspartylalanine were not present at concentrations above 1 microM.