Search PubMed⌕ Search

Biomedical subjects

A Rich

Publications and source records attributed to A Rich.

At least 397 records · Page 22Linked to original sources
PubMed1972

The three-dimensional structure of yeast phenylalanine transfer RNA: shape of the molecule at 5.5-A resolution.

Three isomorphous heavy-atom derivatives have been obtained of orthorhombic crystals of phenylalanine transfer RNA from yeast. These derivatives contain osmium, samarium, and platinum. The positions of the heavy atoms have been determined; these have been used to calculate a three-dimensional electron-density map of transfer RNA at a resolution of 5.5 A. The map shows a high contrast between the molecular boundaries and the solvent areas, so that most of the external shape of the molecule can be determined. The molecule appears to be 92 A long and to have a width varying from 16 A to 34 A. There are some narrow regions in the molecule that connect more globular regions. The electron density map shows chains of dense objects approximately 6 A apart that are probably due to adjacent phosphate groups on the polynucleotide chain. At the present stage of the analysis it is not possible to trace the entire backbone unambiguously; however, the data at this resolution suggest no apparent similarity between the folding of the molecule and any of the tertiary structure models proposed for transfer RNA.

Models, Structural↗
PubMed1972

Proparathyroid hormone: identification of a biosynthetic precursor to parathyroid hormone.

Biosynthesis of a precursor to bovine parathyroid hormone has been demonstrated in slices of parathyroid tissue incubated in vitro. The proparathyroid hormone is 15-20 amino acids larger than the bovine hormone, and has a molecular weight of about 11,500 as determined by polyacrylamide gel electrophoresis. Upon incubation of parathyroid slices with [(14)C]aminoacids, radioactivity is detected initially in the precursor. If incorporation of [(14)C]aminoacids is inhibited after a short incubation either by replacement of radioactive amino acids with unlabeled amino acids or by addition of puromycin, the amount of radioactivity in the precursor decreases, while the radioactivity in the hormone continues to increase. The precursor is bound by an antibody that is specific for parathyroid hormone, and its binding can be inhibited by addition of the hormone. Analysis of tryptic digests indicates that the precursor and the hormone have common tryptic peptides, and that there are at least two additional peptides in the precursor.

Amino Acids↗
PubMed1971

Ribosome-catalyzed polyester formation.

Deamination of phenylalanyl-transfer RNA with nitrous acid yields the alpha-hydroxyacyl analog, phenyllactyl-transfer RNA. When this is incubated in a protein-synthesizing system directed by polyuridylic acid, it yields an acid-precipitable, alkali-labile polyester of phenyllactic acid.

Biotransformation↗
PubMed1971

Size changes in eukaryotic ribosomes.

Evidence is presented that ribosomes active in protein synthesis and attached to messenger RNA on polysomes have a smaller diameter than free cytoplasmic single ribosomes. Measurements have been made on these two types of ribosomes of differences in sedimentation velocity and diffusion constant. Differences in these quantities suggest about a 20-A decrease in the diameter of the ribosomes from chick embryo muscles when they are attached to messenger RNA. Similar differences are also observed in rabbit reticulocytes and mouse ascites tumor cells. These two ribosomal states have different sensitivity to Pronase digestion and dissociate into ribosomal subunits at different KCl concentrations. This size difference is not associated with a significant difference in overall ribosomal mass and appears not to be dependent upon the presence of nascent polypeptide chains.

Animals↗
PubMed1971

High-resolution x-ray diffraction patterns of crystalline transfer RNA that show helical regions.

Yeast phenylalanyl transfer RNA crystallizes in a simple orthorhombic unit cell (a = 33.2, b = 56.1, c = 161 A), and the crystal yields an x-ray diffraction pattern with a resolution of 2.3 A. From an analysis of the packing in the unit cell it is concluded that the molecular dimensions are approximately 80 by 33 by 28 A. The diffraction pattern viewed along the a-axis has a distribution characteristic of double-helical nucleic acids. However, this distribution is not found when the pattern is viewed along the b-axis. This has been interpreted as indicating that the double-helical portions of the transfer RNA molecule are approximately half a helical turn in length, and therefore can contain 4-7 base pairs. These results are consistent with the cloverleaf formulation of transfer RNA secondary structure.

Crystallization↗
PubMed1971

The crystal and molecular structure of an intermolecular complex between riboflavin and an adenosine derivative.

Riboflavin and the adenosine derivative 5'-bromo-5'-deoxyadenosine form a crystalline 1:1 intermolecular complex, the structure of which has been solved by x-ray diffraction analysis. The adenine ring is found to be joined by two hydrogen bonds to the uracillike end of the riboflavin isoalloxazine ring. In addition, the riboflavin and the adenosine molecules associate through the formation of stacks of alternating parallel adenine and isoalloxazine rings. These intermolecular associations are considered to be models for intramolecular association in the coenzyme flavin adenine dinucleotide (FAD), which contains both adenosine and riboflavin.

Adenosine↗