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Biomedical subjects

E D Murray

Publications and source records attributed to E D Murray.

26 records · Page 2Linked to original sources
PubMed1987

Chimeric mouse-human IgG1 antibody that can mediate lysis of cancer cells.

A chimeric mouse-human antibody has been created that recognizes an antigen found on the surface of cells from many carcinomas. Immunoglobulin constant (C) domains of the mouse monoclonal antibody L6, C gamma 2a and C kappa, were substituted by the human C gamma 1 and C kappa by recombining cDNA modules encoding variable or C domains. The cDNA constructs were transfected into lymphoid cells for antibody production. The chimeric antibody and mouse L6 antibody bound to carcinoma cells with equal affinity and mediated complement-dependent cytolysis. In the presence of human effector cells, the chimeric antibody gave antibody-dependent cellular cytotoxicity at 100 times lower concentration than that needed for the mouse L6 antibody. The chimeric antibody, but not the mouse L6 antibody, is effective against a melanoma line expressing small amounts of the L6 antigen. The findings point to the usefulness of the chimeric antibody approach for obtaining agents with strong antitumor activity for possible therapeutic use in man.

Amino Acid Sequence↗
PubMed1987

Thermal properties of chemically modified cytochrome c.

Differential scanning calorimetry was used as a probe to follow structural disturbances in cytochrome c with electrostatic modification. At 51.7% maleylation, the Td decreased 14.1 degrees C; however, relatively stable delta H values reflected minor structural variations. With 77.5 and 96.4% modification, a significant decrease in delta H was more indicative of major conformational change. On this basis, a critical labelling point was considered. Extensive maleylation (96.4%) did not result in complete cytochrome denaturation. In general, assessment of cytochrome thermal parameters by DSC provided a conformational perspective for the influence of specific electrostatic parameters on molecular integrity.

Animals↗
PubMed1986

Metabolism of a synthetic L-isoaspartyl-containing hexapeptide in erythrocyte extracts. Enzymatic methyl esterification is followed by nonenzymatic succinimide formation.

The synthetic peptide, L-Val-L-Tyr-L-Pro-L-isoAsp-Gly-L-Ala, is a substrate for the erythrocyte and brain protein carboxyl methyltransferases. These enzymes catalyze the methyl esterification of the free alpha-carboxyl group of the isoaspartyl residue, to which the glycyl residue is linked through the side chain beta-carboxyl group. In this work, we show that the alpha-methyl ester of this peptide was rapidly demethylated (t1/2 = 4 min at 37 degrees C, pH 7.4) in erythrocyte cytosolic extracts and that the product of this reaction appears to be the succinimide ring derivative of the peptide. The rate of demethylation, measured at either pH 6.0 or 7.4, was the same in buffer and erythrocyte extracts, suggesting that succinimide formation was a nonenzymatic reaction. The L-succinimide is more stable than the ester, but can be hydrolyzed in buffer at pH 7.4 (t1/2 = 180 min at 37 degrees C) to give a mixture of about 75% isoaspartyl peptide and 25% normal aspartyl peptide. The metabolism of the succinimide hexapeptide in erythrocyte extracts appears to be more complex, however. The implications of this work for the methylation and demethylation of cellular proteins containing structurally altered aspartyl residues are discussed.

Chemical Phenomena↗
PubMed1984

Synthetic peptide substrates for the erythrocyte protein carboxyl methyltransferase. Detection of a new site of methylation at isomerized L-aspartyl residues.

Four hexapeptides of sequence L-Val-L-Tyr-L-Pro-(Asp)-Gly-L-Ala containing D- or L-aspartyl residues in normal or isopeptide linkages have been synthesized by the Merrifield solid-phase method as potential substrates of the erythrocyte protein carboxyl methyltransferase. This enzyme has been shown to catalyze the methylation of D-aspartyl residues in proteins in red blood cell membranes and cytosol. Using a new vapor-phase methanol diffusion assay, we have found that the normal hexapeptides containing either D- or L-aspartyl residues were not substrates for the human erythrocyte methyltransferase. On the other hand, the L-aspartyl isopeptide, in which the glycyl residue was linked in a peptide bond to the beta-carboxyl group of the aspartyl residue, was a substrate for the enzyme with a Km of 6.3 microM and was methylated with a maximal velocity equal to that observed when ovalbumin was used as a methyl acceptor. The enzyme catalyzed the transfer of up to 0.8 mol of methyl groups/mol of this peptide. Of the four synthetic peptides, only the L-isohexapeptide competitively inhibits the methylation of ovalbumin by the erythrocyte enzyme. This peptide also acts as a substrate for both of the purified protein carboxyl methyltransferases I and II which have been previously isolated from bovine brain (Aswad, D. W., and Deight, E. A. (1983) J. Neurochem. 40, 1718-1726). The L-isoaspartyl hexapeptide represents the first defined synthetic substrate for a eucaryotic protein carboxyl methyltransferase. These results demonstrate that these enzymes can not only catalyze the formation of methyl esters at the beta-carboxyl groups of D-aspartyl residues but can also form esters at the alpha-carboxyl groups of isomerized L-aspartyl residues. The implications of these findings for the metabolism of modified proteins are discussed.

Amino Acid Sequence↗
PubMedDate not supplied

Has the elusive "natriuretic factor" been discovered, and if so, is it a hormone?

This review summarizes the interesting and significant papers reported at the International Conference on Natriuretic and Digitalis-like Factors held at the ASH meeting in San Francisco, June 1-2, 1997. This area of investigation has been rejuvenated as of late with near structural determination of two ouabain-like isolates from human plasma (OLF) and bovine hypothalamus (HIF) which are apparently the same compound and the isolation and structural elucidation of a natriuretic metabolite of gamma-tocopherol. Spectroscopic information has also been obtained for two other compounds, an ouabain-like factor from bovine adrenals and HHIF from the hypothalamus. An explanation was offered for how low concentrations of digitalis-like factors can regulate vascular reactivity when the predominant isoform of the sodium pump has a low affinity for these compounds. Various groups are examining possible in vivo synthetic pathways that could lead to the production digitalis-like factors. The natriuretic metabolite of gamma-tocopherol, LLU-alpha, fits deWardener's postulates for a natriuretic hormone and is being examined for its involvement in ECF control. Once the structures for some of these ouabain-like compounds are determined and they are synthesized, these compounds will also be able to be studied employing classical pharmacologic methods.

Animals↗