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P Pinphanichakarn

Publications and source records attributed to P Pinphanichakarn.

9 recordsLinked to original sources
PubMed1978

GTP hydrolysis during methionyl-tRNAf binding to 40 S ribosomal subunits and the site of edeine inhibition.

Three lines of evidence are presented indicating that GTP hydrolysis associated with eukaryotic peptide initiation occurs in the absence of 60 S subunits when methionyl-tRNAf is bound to 40 S ribosomal subunits. An enzyme fraction required for binding of methionyl-tRNAf to 40 S subunits and peptide initiation, tentatively equated with eIF-(4 + 5), has GTPase activity and appears to be responsible for hydrolysis of GTP in the methionyl-tRNAf.eIF-2.GTP complex. Direct analysis of the methionyl-tRNAf.40 S complex formed with with eIF-2 and [8-3H] guanine, [gamma-32P]GTP reveals bound guanine but not gamma-phosphate. Edeine, a peptide antibiotic containing spermidine and beta-tyrosine residues at its COOH terminus and NH2 terminus, respectively, blocks peptide initiation and interferes with binding of methionyl-tRNAf to 40 S ribosomal subunits. Inhibition of binding is observed when the eIF-2-mediated binding reaction is carried out with GTP but not with guanosine 5'-(beta,gamma-methylene)triphosphate or guanosine 5'-(beta,gamma-imido)triphosphate. Edeine was labeled by iodination and shown to bind with high affinity to 40 S but not to 60 S ribosomal subunits. It is suggested that edeine blocks a specific site on the 40 S ribosomal subunit to which a segment of the methionyl-tRNAf molecule is bound during the course of the initiation reaction sequence.

Animals↗
PubMed1977

Partial purification and characterization of a translational inhibitor from Friend leukemia cells.

A translational inhibitor has been isolated from unstimulated Friend leukemia cells. The inhibitor is a heat-labile, sulfhydryl reagent-insensitive protein with a molecular weight of approximately 214,000. It inhibits protein synthesis at a step of peptide chain initiation by preventing initiation factor-dependent binding of methionyl-tRNAf to 40 S ribosomal subunits. However, it does not interfere with the formation of the ribosome-independent ternary complex between the initiation factor IF-E2, methionyl-tRNAf, and GTP. The inhibitor preparation contains protein kinase activity which phosphorylates the smallest subunit of IF-E2. There appears to be a functional similarity between this inhibitor from Friend leukemia cells and the hemin-controlled repressor from reticulocytes.

Animals↗
PubMed1977

Partial reaction of peptide initiation inhibited by phosphorylation of either initiation factor eIF-2 or 40S ribosomal proteins.

Preparations of the hemin-controlled repressor (HCR) from rabbit reticulocytes contain 3':5'-cyclic-AMP-independent protein kinase activity for the smallest subunit of the peptide initiation factor eIF-2 and for proteins of reticulocyte 40S ribosomal subunits. Binding of the ternary complex formed between Met-tRNAf, GTP, and eIF-2 to 40S ribosomal subunits is shown to be inhibited by phosphorylation of either the ribosomal subunits or eIF-2. The protein kinase activity responsible for phosphorylation of eIF-2 has been separated from the activity for phosphorylation of 40S ribosomal subunits and shown to independently block the same partial reaction of peptide initiation. It appears that different enzymes are involved, each capable of regulating peptide initiation at the same step but by a different mechanism.

Animals↗
PubMed1975

Globin mRNA translation on Artemia salina ribosomes with components from Friend leukemia cells.

Globin mRNA can be translated with relatively high efficiency in a fractionated cell-free system containing ribosomes prepared from cytst of Artemia salina. These ribosomes have unusually low endogenous activity for peptide synthesis in the absence of added mRNA. The system requires components from the postribosomal supernatant and from the 0.5 M KCl ribosomal wash fraction. Both these fractions were derived from either rabbit reticulocytes or unstimulated Friend leukemia cells that produce little or no hemoglobin. The activity of mRNA and enzyme fractions from rabbit reticulocytes and Friend leukemia cells were tested in this system in vitro for their ability to direct the synthesis of the alpha and beta chains of globin. The alpha:beta chain ratio synthesized from mRNA in the rabbit reticulocyte salt wash fraction was 4:1. The corresponding value for the 9-S mRNA fraction from the salt-washed reticulocyte ribosomes was 1:4, thus these two fractions appear to provide sources enriched in either alpha or beta globin mRNA. Under all conditions tested, the ratio and amounts of peptides formed in vitro appear to reflect mRNA composition. Globin mRNA from dimethysulfoxide-stimulated Friend leukemia cells when translated in vitro produced alpha and beta chains in a ratio of 1:1. These peptides are formed in the same ratio in the intact cells.

Animals↗