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Biomedical subjects

H R Arnstein

Publications and source records attributed to H R Arnstein.

At least 91 records · Page 5Linked to original sources
PubMed1973

The presence of N-terminal methionine on nascent protein of rat liver and rabbit reticulocytes and its cleavage during polypeptide-chain elongation.

1. The size of nascent globin peptides from which the N-terminal methionine residue is cleaved has been investigated by comparing the proportion of N-terminal methionine and valine in short and long chains. Nascent chains were labelled in rabbit reticulocyte lysates, fractionated according to length by chromatography on Sephadex G-50, and analysed by the Edman degradation of selected pooled fractions. It was found that different peptide fractions contained either methionine or valine, but not both, as the N-terminal residue. Methionine was present at the N-terminus of globin chains containing up to approx. 50 amino acids whereas valine was found to be the N-terminal amino acid of longer peptides. 2. In similar experiments with nascent proteins of rat liver, labelled either in vivo or in a cell-free system containing microsomal material and cell sap, evidence was obtained for the presence of methionine at the N-terminus of nascent chains up to approx. 65 amino acid residues long. Thus protein synthesis in liver appears to be initiated also by methionine, but in this case cleavage takes place somewhat later during peptide elongation than in globin synthesis.

Amino Acids↗
PubMed1969

The initiation of haemoglobin synthesis in rabbit reticulocytes.

1. The incorporation of labelled valine by rabbit reticulocytes into the N-terminal position of nascent haemoglobin was investigated by deaminating the nascent peptides with nitrous acid and isolating labelled alpha-hydroxyisovaleric acid and valine after acid hydrolysis. 2. The amount of radioactivity in alpha-hydroxyisovaleric acid relative to that in valine indicated the presence of 12.3% N-terminal valine having a free amino group. This high value suggests that most if not all nascent peptides contain valine in the N-terminal position. 3. Cell-free preparations containing reticulocyte ribosomes and pH5 enzymes incorporated alpha-hydroxy-[(14)C]isovaleryl-tRNA (where tRNA refers to transfer RNA), which was obtained by deamination of [(14)C]valyl-tRNA from yeast or liver with nitrous acid, into both soluble and nascent protein. 4. When the soluble protein was chromatographed on CM-cellulose, radioactivity was found to be associated with both the alpha-and beta-globin chains. 5. The kinetics of hydrolysis of [(14)C]valine, was also investigated. Most of the material was hydrolysed rapidly at pH10, but a minor component that was relatively stable appeared to be present to the extent of about 10% of the total valyl-tRNA. Valine was, however, the only hydrolysis product detected by paper chromatography. 6. It is concluded that chain initiation in haemoglobin synthesis involves valine as the N-terminal amino acid and that the amino group of nascent protein is probably not substituted.

Animals↗
PubMed1965

A comparison of methods for the isolation and fractionation of reticulocyte ribosomes.

1. Polysomes, ribosomes and pH5 enzymes were isolated from rabbit reticulocytes by acidifying the post-mitochondrial supernatant to pH6.0 to precipitate all ribonucleoprotein particles and about half the pH5 enzymes; the precipitate was redissolved in buffer, pH7.6, and fractionated by zone centrifuging. 2. The isolation of polysome-rich and ribosome-rich fractions from the post-mitochondrial supernatant was also examined. 3. Studies of the stability of polysomes revealed that dissociation into sub-units occurred when both bound and free Mg(2+) was chelated by EDTA or when the pH was increased above pH8.8.

Animals↗