Biomedical subjects

V S Reed

Publications and source records attributed to V S Reed.

3 recordsLinked to original sources

PubMed1994

Mechanisms of the transfer of aminoacyl-tRNA from aminoacyl-tRNA synthetase to the elongation factor 1 alpha.

Aspartylation of mammalian tRNAAsp by bacteria-expressed human aspartyl-tRNA synthetase (hDRS) was examined. The kinetics of the aspartylation of tRNA was consistent with the following reaction pathway, [formula: see text] where E, represents aspartyl-tRNA synthetase. A set of rate constants was obtained which fit single turnover time courses at varying concentrations of the enzyme, tRNA, and AMP using the SAAM program. The dissociation of Asp-tRNA (k3) was found to be rate limiting. The elongation factor 1 alpha (EF1 alpha) and GTP stimulated the hDRS aspartylation. The stimulation depended on the presence of both EF1 alpha and GTP. Kinetic analysis indicated that EF1 alpha formed a complex with the hDRS-Asp-tRNA complex and stimulated the dissociation of Asp-tRNA. In the presence of 0.5 M NH4Cl, which enhances the binding of Asp-tRNA by EF1 alpha, hDRS-bound Asp-tRNA can be transferred directly to EF1 alpha. The implications of these results on the function of the multi-tRNA synthetase complex will be discussed.

Amino Acyl-tRNA Synthetases↗

PubMed1994

Characterization of a novel N-terminal peptide in human aspartyl-tRNA synthetase. Roles in the transfer of aminoacyl-tRNA from aminoacyl-tRNA synthetase to the elongation factor 1 alpha.

The kinetics of the N-terminal 32 residue-deleted human aspartyl-tRNA synthetase (hDRS delta 32) was analyzed. The kinetics of aspartyl-adenylate formation and Asp-tRNA synthesis by hDRS delta 32 were indistinguishable from those of hDRS. However, the dissociation of Asp-tRNA from hDRS delta 32 was much faster than that of hDRS. Unlike hDRS delta 32-catalyzed aspartylation of tRNA was not affected by the elongation factor 1 alpha. Two N-terminal peptides of hDRS, hDRS(T5-E26) and hDRS(D12-R27), were synthesized. Both peptides bind to tRNA-Sepharose. Both peptides, hDRS(T5-E26) and hDRS(D12-R27), are monomeric and oligomerize at high peptide concentration or in 50% propylene glycol. The peptide hDRS(T5-E26) showed little alpha-helical content as analyzed by CD spectroscopy, while hDRS(D12-R27) showed appreciable alpha-helical contents in nonpolar solvents. These results suggest that the N terminus in hDRS may mediate the slow release of Asp-tRNA and facilitate the interaction of the hDRS.Asp-tRNA complex with the elongation factor 1 alpha. The demonstration of alpha-helix formation of the hDRS N-terminal peptide is consistent with the hypothetical amphiphilic helix of the N-terminal extension in hDRS. A model for the transfer of Asp-tRNA from hDRS to elongation factor 1 alpha is presented.

Amino Acid Sequence↗

PubMed1976

Pictorial superiority effect.

Pictures generally show superior recognition relative to their verbal labels. This experiment was designed to link this pictorial superiority effect to sensory or meaning codes associated with the two types of symbols. Paired-associate stimuli consisted of simple pictures or of their labels, with list items selected either from the same conceptual category or from different conceptual categories. In addition, schematic or visual similarity among the pictures was either high or low. At two rates of presentation equal amounts of conceptual interference were produced for pictures and their labels. High schematic similarity eliminated the pictorial superiority effects at the slow rate and completely reversed it at the fast rate. These results suggest that the meaning representations for simple pictures and their labels may be identical, and that the pictorial superiority effect is related to the qualitative superiority of the sensory codes for pictures.

Concept Formation↗