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Biomedical subjects

G N Cohen

Publications and source records attributed to G N Cohen.

At least 19 recordsLinked to original sources
PubMed1979

Some properties of Escherichia coli glutamine synthetase after limited proteolysis by subtilisin.

Escherichia coli glutamine synthetase is inactivated by subtilisin. Protection against inactivation is afforded by glutamine and ammonium ions. One large fragment (Mr = 35,000) is identified by sodium dodecyl sulfate-gel electrophoresis and carries adenylylation site. Smaller quantities of two other fragments (Mr = 17,000 and 15,000, respectively) are als observed oo observed on the gel. tthe nicked protein remains dodecameric, as evidenced by electrophoresis and centrifugation. It has retained the binding properties toward ADP and Ci-bacron blue and undergoes conformation changes upon binding, as does the intact protein. It is recognized by the antiserum raised against the native enzyme. The nicked protein also remains an excellent substrate of E. coli adenylyltransferase.

Escherichia coli↗
PubMed1978

The primary structure of Escherichia coli K12 aspartokinase I-homoserine dehydrogenase I. Site of limited proteolytic cleavage by subtilisin.

The sequence of the first 25 residues of the homoserine dehydrogenase fragment, produced by limited proteolysis of aspartokinase I-homoserine dehydrogenase I with substilisin, has been determined. The sequence of a cyanogen bromide peptide (CB5, 59 residues), isolated from the entire protein, is also presented. Residues 1 to 18 of the subtilisin homoserine dehydrogenase fragment match the sequence 42 to 59 of peptide CB5.

Amino Acid Sequence↗
PubMed1978

Detection of the homology among proteins by immunochemical cross-reactivity between denatured antigens. Application to the threonine and methionine regulated aspartokinases-homoserine dehydrogenases from Escherichia coli K 12.

The two isofunctional enzymes aspartokinases-homoserine dehydrogenases I and II from Escherichia coli K 12 are compared using immunochemical techniques. The antibodies raised against one of these two proteins when in its native state can only recognize the homologous antigen, whether it is native or denatured. Contrarily, the antibodies raised against one of these two proteins when in its denatured state can recognize both the homologous and heterologous denatured antigens. The existence of this cross-reaction only between the two denatured aspartokinases-homoserine dehydrogenases suggests that these two enzymes have some similarity since such a reaction is not detected with several other denatured proteins. The regions involved in this similarity are buried inside the native proteins, and become exposed only upon denaturation. The same results, the existence of a cross-reaction between denatured species and none between the native ones, is obtained with proteolytic fragments derived from these two proteins and endowed with homoserine dehydrogenase activity. This resemblance between the two aspartokinases-homoserine dehydrogenases suggests that these proteins derive from a common ancestor. It is also proposed that such a cross-reaction between two denatured proteins is evidence for an homology between their amino acid sequences, and that the use of denatured proteins as both immunogens and antigens could be useful in detecting sequence homologies.

Alkylation↗
PubMed1978

The primary structure of Escherichia coli K12 aspartokinase I-homoserine dehydrogenase I-Isolation and characterisation of the peptides produced by cyanogen bromide.

The aspartokinase I-homoserine dehydrogenase I from Escherichia coli K12, composed of four identical subunits of molecular weight 86,000, was carboxy-methylated, fragmented by cyanogen bromide treatment and citraconylated. Using gel filtration, ion exchange chromatography and preparative paper electrophoresis and chromatography, 15 of 21 cyanogen bromide peptides were isolated in pure form and characterized by their composition, their N-terminal amino acid, and by their content of known cysteinyl or tryptophanyl tryptic peptides.

Alkylation↗
PubMed1978

Hypersensitivity to five non-steroidal anti-inflammatory agents: ibuprofen, fenoprofen, indomethacin, naproxen and tolmetin.

Five drugs promoted generally as safe substitutes for aspirin-sensitive individuals (ASA) were studied. All five were found capable of causing exacerbation of symptoms and increase of induced bleeding time in ASA patients with concomitant low iodide tolerance, and four of the five drugs gave positive reactions in patients tolerant to ASA but iodide intolerant.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1977

Proteolysis of the bifunctional methionine-repressible aspartokinase II-homoserine dehydrogenase II of Escherichia coli K12. Production of an active homoserine dehydrogenase fragment.

The dimeric bifunctional enzyme aspartokinase II-homoserine dehydrogenase II (Mr = 2 X 88,000) of Escherichia coli K12 can be cleaved into two nonoverlapping fragments by limited proteolysis with subtilisin. These two fragments can be separated under nondenaturing conditions as dimeric species, which indicates that each fragment has retained some of the association areas involved in the conformation of the native protein. The smaller fragment (Mr = 2 X 24,000) is devoid of aspartokinase and homoserine dehydrogenase activity. The larger fragment (Mr = 2 X 37,000) is endowed with full homoserine dehydrogenase activity. These results show that the polypeptide chains of the native enzyme are organized in two different domains, that both domains participate in building up the native dimeric structure, and that one of these domains only is responsible for homoserine dehydrogenase activity. A model of aspartokinase II-homoserine dehydrogenase II is proposed, which accounts for the present results.

Alcohol Oxidoreductases↗
PubMed1977

Subunit structure of the methionine-repressible aspartokinase II--homoserine dehydrogenase II from Escherichia coli K12.

The quaternary structure of Escherichia coli K12 aspartokinase II--homoserine dehydrogenase II has been examined. This multifunctional protein has a molecular weight Mr = 176000. It is composed of two subunits having the same molecular weight and the same charge. The results obtained from the examination of tryptic maps, the number and amino acid composition of cysteine-containing peptides and the uniqueness of the N-terminal sequence, strongly suggest that the 2 subunits are identical. The properties of aspartokinase II--homoserine dehydrogenase II can be compared to those of the much better known protein aspartokinase I--homoserine dehydrogenase I.

Amino Acid Sequence↗
PubMed1977

Threonyl-transfer ribonucleic acid synthetase and the regulation of the threonine operon in Escherichia coli.

Two threonine-requiring mutants with derepressed expression of the threonine operon were isolated from an Escherichia coli K-12 strain containing two copies of the thr operon. One of them carries a leaky mutation in ilvA (the structural gene for threonine deaminase), which creates an isoleucine limitation and therefore derepression of the thr operon. In the second mutant, the enzymes of the thr operon were not repressed by threonine plus isoleucine; the threonyl-transfer ribonucleic acid(tRNA) synthetase from this mutant shows an apparent Km for threonine 200-fold higher than that of the parental strain. The gene, called thrS, coding for threonyl-tRNA synthetase was located around 30 min on the E. coli map. The regulatory properties of this mutant imply the involvement of charged threonyl-tRNA or threonyl-tRNA synthetase in the regulation of the thr operon.

Amino Acyl-tRNA Synthetases↗
PubMed1977

Serum triglyceride and cholesterol levels and lipid electrophoretic patterns in intrinsic and extrinsic allergic states.

This study indicates that hypertriglyceridemia and associated pre-beta hyperlipidemia (Fredrickson's type IV lipid pattern) is frequently associated with intrinsic allergic disease characterized by chemical intolerant (hypersensitivity) states, particularly of the aspirin intolerant type and to a somewhat lesser extent with the butylated hydroxyanisole and butylated hydroxytoluene intolerant type, as well as the iodide intolerant state. It confirms that diabetics suffering concomitantly with extrinsic or intrinsic allergic disease still continue to demonstrate a high occurrence of this type of hypertriglyceridemia. In contrast, pure atopic, extrinsic-allergic patients demonstrated a very low incidence of type IV hyperlipoproteinemia. The interrelationships of these findings with previously reported metabolic abnormalities in intrinsic allergic hypersensitivity states is correlated.

Adult↗
PubMed1977

Chronic and recurrent urticaria: new concepts of drug-group sensitivity.

From further studies on identification of etiologies in chronic and recurrent urticaria, two conclusions stand out: (1) that multiple, differing drugs and chemicals may form a single family group, with cross-hypersensitivity to other substances within the group and (2) that many patients tend to develop hypersensitivity to substances in multiple groups.

Aspirin↗
PubMed1977

A vascular test to detect iodide hypersensitivity (intolerance).

Reliance upon conventional skin testing to detect hypersensitivity to iodides has proved unreliable. Present intravenous challenge methods often are inadequate and add an additional risk factor. This report describes an in vivo testing procedure that is safer because, other than for experimental corroboration of this method by direct iodide challenges, the use of non-iodide containing challenge material can be substituted to accurately detect possible iodide intolerance. Thus this procedure uses a parameter of measurement that does not require the eliciting of clinical symptoms by direct iodide challenge.

Aspirin↗
PubMed1976

Homoserine kinase from Escherichia coli K12.

Homoserine kinase was purified to apparent homogeneity from a derepressed strain of Escherichia coli K12, using standard fractionation techniques. It is a dimer (Mr = 60000) composed of apparently identical polypeptide chains (Mr = 29000). Its amino acid composition and N-terminal sequence have been determined. L-Threonine is a competitive inhibitor of the substrate L-homoserine; this inhibition is straighforward and shows no sign of co-operativity. Evidence is presented that homoserine and threonine bind to the same site of this non-allosteric enzyme. The binding of homoserine and threonine can also be studied by difference spectroscopy; the latter studies reveal an unexpected effect of magnesium ions, which might be the basis for the unusual high Mg2+ requirement for optimal enzyme reaction.

Amino Acid Sequence↗
PubMed1976

A serum factor in aspirin intolerance disease.

Direct and indirect intradermal serum challenge with aspirin intolerant sera in both aspirin tolerant and intolerant patients demonstrated a heat, cold and storage stable serum factor capable of inducing acute anti-hemostatic effects and in some aspirin intolerant patients exacerbation of brief induced clinical symptoms. The data supports a hypothesis for possible induced, conformationally altered gamma globulin resulting from low molecular weight chemical exposures such as aspirin with ensuing recognition by a genetically determined subpopulation of B-lymphocytes with surface membrane receptors avid for the Fc portion of altered gamma globulin or some conformationally altered gamma globulin fraction leading to immune and/or interprotein complexes with subsequent alterations of adrenergic, cholinergic and/or metabolic pharmacologic pathways.

Aspirin↗