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Biomedical subjects

A Neuberger

Publications and source records attributed to A Neuberger.

63 records · Page 4Linked to original sources
PubMed1968

The effect of adenosine triphosphate on porphyrin excretion and on glycine metabolism in Rhodopseudomonas spheroides.

1. ATP, GTP, CTP and UTP at concentrations of 1mm markedly decrease the amount of coproporphyrin excreted by Rhodopseudomonas spheroides illuminated in a medium containing glycine, succinate and fumarate. 2. The effect of ATP is decreased if ethionine is also added to the medium. 3. Evidence is presented showing that ATP is taken up by the organisms from the medium. 4. ATP is shown to have a marked effect on the utilization of glycine. In the presence of ATP the incorporation of the methylene carbon atom of glycine into the fatty acid moieties of the phospholipids is greatly increased, and more of the carboxyl carbon atom is lost, probably as carbon dioxide. 5. ATP has little effect on the utilization of succinate or fumarate. 6. The possible significance of these results with regard to the control by ATP of porphyrin synthesis and excretion and glycine metabolism is discussed.

Adenosine Triphosphate↗
PubMed1968

The estimation of galactose, mannose and fucose in glycoproteins by radioisotope dilution.

1. The principle of radioisotope dilution, as used previously for the estimation of mannose in egg albumin, was applied on a semi-micro scale to the estimation of fucose, mannose and galactose in some glycoproteins. The sugars were separated by partition chromatography on columns of Celite 545. 2. The release of mannose from egg albumin in 2n-hydrochloric acid at 100 degrees after various times was determined by the radioisotope-dilution method and found to have a half-time of 7min. 3. The destruction of mannose in 2n-hydrochloric acid after 3hr. at 100 degrees was found to be small if air was excluded. The destruction was slightly increased by the presence of lysozyme containing tryptophan in an amount equimolar with the mannose. The same amount of free tryptophan caused considerable loss of mannose. 4. Analytical values are reported for the non-amino sugar contents of egg albumin, rabbit gamma-globulin and some samples of blood-group-specific substances. The values found were similar to the most reliable estimates published previously.

Animals↗
PubMed1968

The determination of glucosamine and galactosamine in some glycoproteins by radioisotope dilution.

1. The principle of radioisotope dilution was applied on a semi-micro scale to the determination of glucosamine and galactosamine in some glycoproteins, such as immunoglobulins, a urinary glycoprotein and blood-group-specific substances. 2. The glycoprotein was hydrolysed in the presence of [1-(14)C]glucosamine or [1-(14)C]galactosamine or both. The amino sugars were made to react with naphthyl isothiocyanate and the products formed were isolated by the method of Scott (1962). The specific radioactivities determined from liquid-scintillation counting and the extinction at 240mmu or 222mmu were used to calculate the content of amino sugars in the protein analysed. 3. Where the values could be compared with those found by other workers, differences were in general not very great. The advantages of the method are that high concentrations of acid can be employed and undesirable side reactions, which may occur with the free sugars, do not affect the results. A potential source of error of the method is discussed.

Carbon Isotopes↗
PubMed1966

Effect of lipids and organic solvents on the enzymic formation of zinc protoporphyrin and haem.

1. Differences observed in earlier work between the enzymic chelation with protoporphyrin of Zn(2+) and Fe(2+) ions respectively have now been explained as being caused by the presence of peroxides in the ether used in the enzyme assay. The inhibitory effect of peroxides is established by the reducing agent, which is present in the assay for chelation of iron but not in that for zinc. There are now no reasons for the belief that two different enzymes catalyse formation of complexes with zinc and iron respectively. 2. Removal of lipid from both chromatophores and mitochondria markedly reduced chelatase activity. Activity could be partially restored by the addition of lipid fractions. Phosphatidic acid, but not phosphatidylcholine or phosphatidylethanolamine, actively stimulated the formation of zinc protoporphyrin and haem by chromatophores and mitochondrial preparations. 3. Lipid-containing extracts of chromatophores, and fractions thereof obtained by silicic acid chromatography, partially restored chelatase activity of Tween extracts of mitochondria. Thus, although both enzymes are considered to be lipoproteins, the identity of the lipids concerned is still uncertain. 4. A great number of organic solvents such as esters, ethers, ketones and, to a lesser extent, alcohols, stimulate enzymic chelation of both metals with protoporphyrin. A number of explanations for these findings are considered and it is suggested that organic solvents interact in some way with the enzyme lipoprotein, changing either its conformation or allowing closer contact between the enzyme and its substrates.

Acetates↗