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Query: UNIPROT:P01350 (gastrin)
 9,683 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In dogs with gastric fistulae and with transposition of the portal vein and the inferior vena cava, we studied secretion of acid in response to portal or systemic venous infusion of a series of progressively longer fragments of the carboxyl terminal portion of human gastrin. Pentagastrin, G6, G7, G8, G9, G10, G13, G17, and G34 were studied. Potency by portal venous infusion relative to systemic venous infusion was used as an index of hepatic inactivation. Fragments with eight or fewer amino acid residues were more than 90% inactivated by hepatic transit. Fragments with nine or more amino acid residues were more resistant to hepatic inactivation than shorter fragments. For fragments with 7 to 17 amino acid residues, increasing the chain length was accompanied by progressive increase both in hepatic resistance to inactivation and in potency for stimulation of acid secretion, suggesting that resistance to hepatic inactivation may be a major determinant of potency.
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PMID:Hepatic inactivation of gastrins of various chain lengths in dogs. 63 85

The nucleotides in Escherichia coli tRNA(Phe) required for recognition by its cognate synthetase have been determined in vitro by measuring the kinetic parameters for aminoacylation using mutant tRNA(Phe) transcripts with purified E. coli tRNA(Phe) synthetase. The substitution of 11 nucleotides in E. coli tRNA(Phe) is shown to decrease the kcat/KM by as much as 1000-fold relative to the wild type. The most important recognition elements are the three anticodon nucleotides G34, A35, and A36. The recognition set also includes nucleotides in the variable pocket (U20 and U59), the acceptor end (A73), and the tRNA central core (G10, C25, A26, G44, and U45). Many of the recognition nucleotides are also among the residues comprising the identity set determined in vivo using an amber suppressor tRNA(Phe) [McClain, W. H., & Foss, K. (1988) J. Mol. Biol. 202, 697-709]. As could be anticipated from the very different methods used, some nucleotides in the identity set determined by the suppressor method were not among the recognition nucleotides and vice versa. The E. coli tRNA(Phe) recognition data can also be compared to the recognition sets for yeast and human tRNA(Phe) determined previously. The results indicate that the mechanism by which phenylalanyl-tRNA synthetases recognize their substrates seems to have diverged somewhat among different species. For example, nucleotide 20 in the D-loop, the anticodon nucleotides and the discriminator base 73 are important for the recognition by all three enzymes. However, recognition of the tRNA central core nucleotides is unique to E. coli FRS.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Determination of recognition nucleotides for Escherichia coli phenylalanyl-tRNA synthetase. 142 Jan 56

Various tRNA transcripts were constructed to study the identity elements of Escherichia coli tRNA(Asp). Base substitutions from G34 to U34 at the first position of the anticodon, and from U35 to A35 at the second, severely impaired the aspartate charging activity. The activity was also decreased, but in a more moderate fashion, by base changes at G2-C71, C36 and C38. Identity nucleotides of tRNA(Asp) are distributed in a different fashion between E. coli and yeast, which occur at the second base pair of the acceptor stem, G10-U25 base pair in the D-stem and 3' half of the anticodon loop.
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PMID:Escherichia coli tRNA(Asp) recognition mechanism differing from that of the yeast system. 147 58

The nucleotides crucial for the specific aminoacylation of yeast tRNA(Asp) by its cognate synthetase have been identified. Steady-state aminoacylation kinetics of unmodified tRNA transcripts indicate that G34, U35, C36, and G73 are important determinants of tRNA(Asp) identity. Mutations at these positions result in a large decrease (19- to 530-fold) of the kinetic specificity constant (ratio of the catalytic rate constant kcat and the Michaelis constant Km) for aspartylation relative to wild-type tRNA(Asp). Mutation to G10-C25 within the D-stem reduced kcat/Km eightfold. This fifth mutation probably indirectly affects the presentation of the highly conserved G10 nucleotide to the synthetase. A yeast tRNA(Phe) was converted into an efficient substrate for aspartyl-tRNA synthetase through introduction of the five identity elements. The identity nucleotides are located in regions of tight interaction between tRNA and synthetase as shown in the crystal structure of the complex and suggest sites of base-specific contacts.
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PMID:Identity elements for specific aminoacylation of yeast tRNA(Asp) by cognate aspartyl-tRNA synthetase. 204 78

We have investigated whether unmodified yeast phenylalanine transfer RNA as well as one of its precursors containing an intron of nineteen nucleotides in the anticodon (pre-tRNA-Phe) can become substrates for selected tRNA modification enzymes present in a eukaryotic cell. This study was done by microinjecting into the cytoplasm of Xenopus laevis oocytes transcripts completely deprived of the naturally occurring modified nucleotides; these were obtained in vitro from appropriate synthetic genes under the control of bacteriophage T7 promoter. During the in vitro transcription, 32P labels were introduced with the guanosine triphosphate thus allowing easy detection of guanosine modifications in tRNA by two-dimensional chromatography after complete digestion into 5'-mononucleotides by nuclease P1. Results indicate that modifications occur on five guanosines (at positions 10, 26, 34, 37 and 46) in yeast tRNA-Phe and only on three guanosines (at 10, 26 and 46) in yeast precursor tRNA-Phe. These are the modifications expected from the known nucleotide sequences of naturally occurring Xenopus and yeast tRNA-Phe, i.e. N2-methyl-G10, N2,N2-dimethyl-G26, 2'-O-methyl-G34, N1-methyl-G37 or Y nucleoside-37 and N7-methyl-G46. The rates of modifications occurring in the two kinds of tRNA-Phe are faster in the intron-less tRNA-Phe than in the intron-containing tRNA-Phe. However quantitative modifications are only observed after as long as 75 h incubation in the oocytes.
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PMID:Guanosine modifications in runoff transcripts of synthetic transfer RNA-Phe genes microinjected into Xenopus oocytes. 220 54

In vitro selection was used to isolate active Escherichia coli tRNA(Phe) variants from randomized libraries. Functional tRNAs were first selected by multiple rounds of binding to Escherichia coli phenylalanyl-tRNA synthetase. These variants were then aminoacylated and selected for affinity to elongation factor-Tu. By randomizing potential recognition nucleotides, the importance of residues U20, G34, A35, A36 and U59, previously identified to be required for specific recognition by E. coli phenylalanyl-tRNA synthetase (FRS), was confirmed. However, the sequences of several active variants imply that the wild-type tertiary interactions G10-C25-U45 and A26-G44 are not required for recognition, as previously suggested. Selection of functional tRNAs from a second library randomized at positions normally involved in conserved tertiary interactions revealed new combinations of nucleotides at these positions, suggesting the presence of novel tertiary interactions. In both libraries, active sequences containing deletions were isolated. Taken together, it is clear that FRS is active with substrates having an unexpectedly broad sequence diversity. Finally, the potency of this method is illustrated by the identification of a second class of variants that was isolated by virtue of the presence of an impurity in the FRS preparation.
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PMID:Selection for active E. coli tRNA(Phe) variants from a randomized library using two proteins. 768 42

Serine tRNA gene derivatives with altered anticodons were introduced to the temperature-sensitive serT42 mutant, whose tRNA(1Ser) shows a base substitution of A10 for wild type G10. When a low copy number vector-system was used, the growth and beta-galactosidase synthetic activity of the serT42 mutant were restored by complementation with the tRNA(5Ser) (T34) gene or the tRNA(1Ser) (G34) gene as well as the tRNA(1Ser) (wt) gene, but not with tRNA(5Ser) (wt), tRNA(1Ser) (A34) or tRNA(1Ser) (C34) genes at 42 degrees C. When multicopy vectors were used, the transformation even with tRNA(1Ser) (A10) gene restored the growth and beta-galactosidase synthetic activity at 42 degrees C. The tRNA(1Ser) (A10) showed no thermosensitivity in serine acceptor activity by in vitro assay. At 42 degrees C, the amount of tRNA(1Ser) (A10) in the serT42 mutant was almost the same as those in the wild type. The nucleotides in the tRNA(1Ser) (A10) were found to be fully modified like those in the wild type tRNA(1Ser). Both of the tRNAs transcribed from tRNA(5Ser) (T34) and tRNA(1Ser) (G34) genes showed serine acceptor activity. Modified nucleosides of these tRNAs were also analyzed.
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PMID:Suppression of the serT42 mutation with modified tRNA(1Ser) and tRNA(5Ser) genes. 806 26

We have investigated the functional relationship between nucleotides in yeast tRNAAsp that are important for aspartylation by yeast aspartyl-tRNA synthetase. Transcripts of tRNAAsp with two or more mutations at identity positions G73, G34, U35, C36 and base pair G10-U25 have been prepared and the steady-state kinetics of their aspartylation were measured. Multiple mutations affect the catalytic activities of the synthetase mainly at the level of the catalytic constant, kcat. Kinetic data were expressed as free energy variation at transition state of these multiple mutants and comparison of experimental values with those calculated from results on single mutants defined three types of relationships between the identity nucleotides of this tRNA. Nucleotides located far apart in the three-dimensional structure of the tRNA act cooperatively whereas nucleotides of the anticodon triplet act either additively or anti-cooperatively. These results are related to the specific interactions of functional groups on identity nucleotides with amino acids in the protein as revealed by the crystal structure of the tRNAAsp/aspartyl-tRNA synthetase complex. These relationships between identity nucleotides may play an important role in the biological function of tRNAs.
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PMID:Additive, cooperative and anti-cooperative effects between identity nucleotides of a tRNA. 833 8

The aspartate identity of tRNA for AspRS from Thermus thermophilus has been investigated by kinetic analysis of the aspartylation reaction of different tRNA molecules and their variants as well as of tRNAPhe variants with transplanted aspartate identity elements. It is shown that G10, G34, U35, C36, C38, and G73 determine recognition and aspartylation of yeast and T.thermophilus tRNA(Asp) by the thermophilic AspRS. This set of nucleotides specifies also tRNA aspartylation in the homologous yeast and Escherichia coli systems. Structural considerations indicate that the major aspartate identity elements interact with amino acids conserved in all AspRSs. It follows that the structural features of tRNA and synthetase specifying aspartylation are mainly conserved in various structural contexts and in organisms adapted to different life conditions. Mutations of tRNA identity elements provoke drastic losses of charging in the heterologous system involving yeast tRNA(Asp) and T. thermophilus AspRS. In the homologous systems, the mutational effects are less pronounced. However, effects in E. coli and T. thermophilus exceed those in yeast which are particularly moderate, indicating variations in the individual contributions of identity elements for aspartylation in prokaryotes and eukaryotes. Analysis of multiple tRNA mutants reveals cooperativity between the cluster of determinants of the anticodon loop and the additional determinants G10 and G73 for efficient aspartylation in the thermophilic system, suggesting that conformational changes trigger formation of the functional tRNA/synthetase complex.
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PMID:Identity of prokaryotic and eukaryotic tRNA(Asp) for aminoacylation by aspartyl-tRNA synthetase from Thermus thermophilus. 865 22

We have searched for millimetre-wave line emission from ethylene oxide (c-C2H4O) and its structural isomer acetaldehyde (CH3CHO) in 11 molecular clouds using SEST. Ethylene oxide and acetaldehyde were detected through multiple lines in the hot cores NGC 6334F, G327.3-0.6, G31.41+0.31, and G34.3+0.2. Acetaldehyde was also detected towards G10.47+0.03, G322.2+0.6, and Orion 3'N, and one ethylene oxide line was tentatively detected in G10.47+0.03. Column densities and rotational excitation temperatures were derived using a procedure which fits the observed line intensifies by finding the minimum chi 2-value. The resulting rotational excitation temperatures of ethylene oxide and acetaldehyde are in the range 16-38 K, indicating that these species are excited in the outer, cooler parts of the hot cores or that the excitation is significantly subthermal. For an assumed source size of 20", the deduced column densities are (0.6-1)x10(14) cm-2 for ethylene oxide and (2-5)x10(14) cm-2 for acetaldehyde. The fractional abundances with respect to H2 are X[c-C2H4O]=(2-6)xl0(-10), and X[CH3CHO]=(0.8-3)x10(-9). The ratio X[CH3CHO]/X[c-C2H4O] varies between 2.6 (NGC 6334F) and 8.5 (G327.3-0.6). We also detected and analysed multiple transitions of CH3OH, CH3OCH3, C2H5OH, and HCOOH. The chemical, and possibly evolutionary, states of NGC 6334F, G327.3-0.6, G31.41+0.31, and G34.3+0.2 seem to be very similar.
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PMID:Abundances of ethylene oxide and acetaldehyde in hot molecular cloud cores. 1154 22


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