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Biomedical subjects

R Silber

Publications and source records attributed to R Silber.

At least 127 records · Page 7Linked to original sources
PubMed1976

Adenosine deaminase activity in chronic lymphocytic leukemia. Relationship to B- and T-cell subpopulations.

The level, phenotypes, and isozyme distribution of adenosine deaminase (ADA) were determined in lymphocytes from patients with chronic lymphocytic leukemia (CLL). The ADA level in lymphocytes from patients with untreated CLL was consistently lower than in lymphocytes from normal subjects. No significant differences were found in the phenotype or isozyme distribution. In untreated patients, the ADA level was inversely correlated with the lymphocyte count and the percentage of bursa-equivalent (B) cells. After therapy, a diminution in the lymphocyte count was associated with an increase of ADA activity towards normal levels. The ADA levels were slightly higher in the thymus-derived (T) than in the B lymphocytes from normal subjects. The B cells had lower activity than T cells in patients with CLL. They also had a lower activity than the B cells from normal subjects. The ADA level was 2.3-fold higher in T cells from patients with CLL than in normal T cells. The decrease in ADA levels is an anomaly that is reversible and appears to be a reflection of the proliferation of abnormal B cells in this disorder.

Adenosine Deaminase↗
PubMed1976

Cyclic adenosine 3':5'-monophosphate phosphodiesterase activity in normal and chronic lymphocytic leukemia lymphocytes.

The specific activity of cyclic adenosine 3':5'-monophosphate phosphodiesterase was measured in lymphocytes isolated from the blood of normal subjects, from patients with chronic lymphocytic leukemia, and from tonsil tissue. The mean specific activity of cyclic adenosine 3':5'-monophosphate phosphodiesterase in the lymphocytes from patients with untreated chronic lymphocytic leukemia was lower than that in lymphocytes from the blood of normal subjects or from tonsils. Cyclic adenosine 3':5'-monophosphate phosphodiesterase levels did not correlate with differences in B- and T-cell lymphocyte subpopulations or with peripheral blood lymphocyte counts.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Function of 5'-nucleotidase in the uptake of adenosine from AMP by human lymphocytes.

The function of 5'-nucleotidase in nucleoside uptake from AMP was investigated in human lymphocytes by comparing the transport in cells containing this enzyme (5'N+) with that in cells deficient in the activity (5'N-). The rate of adenosine and Pi uptake from AMP was 3.9-fold greater in the 5'N+ then in the 5'N- lymphocytes. There was no difference in transport between these cells when incubated with adenosine or Pi. These results indicate that phosphorylytic cleavage of AMP by 5'-nucleotidase is necessary for the uptake of the nucleotide and Pi moieties by the human lymphocyte.

Adenosine↗
PubMed1975

5-methyltetrahydrofolic acid is not a methyl donor for biogenic amines: enzymatic formation of formaldehyde.

Contrary to previous reports, 5-methyltetrahydrofolic acid does not mediate the methylation of dopamine to epinine. Instead, this methyl donor is degraded enzymatically to formaldehyde, which condenses with dopamine to form a tetahydoisoquinoline derivative. The latter has chromotographic characteristics very similar to those of epinine, which likely accounts for the original misidentification of the product.

Animals↗
PubMed1975

Human lymphocytes: 5'-nucleotidase-positive and -negative subpopulations.

The enzyme, 5'-nucleotidase (5'N) (E.C.-3.1.3.5) is present in lymphocytes isolated from the blood of normal subjects. This activity is markedly decreased or not detectable in the cells from three-quarters of patients with chronic lymphocytic leukemia (CLL), while supranormal levels are found in less than 10% of the cases. To determine whether the decreased 5'N value in CLL represents a lower activity per cell or fewer enzyme-containing cells than in the normal, conditions were established for the histochemical measurement of 5'N in human lymphocytes. It was found that the cells isolated from the blood of normal subjects or patients with CLL consist of 5'N-positive and 5'N-negative subpopulations. Normal subjects who had high 5'N specific activity were shown to have a greater percentage of 5'N-positive cells than individuals with low 5'N activity. Patients with CLL who had no activity by standard chemical assay had no 5'N-positive cells, while the exceptional patient with CLL with a higher than normal specific activity showed an percentage of 5'N-positive cells. It is suggested that the selective proliferation of 5'N-positive and 5'N-negative populations may account for the heterogeneity of 5'N in CLL.

Humans↗
PubMed1973

Heterogeneity of 5'-nucleotidase activity in lymphocytes in chronic lymphocytic leukemia.

The specific activity of 5'-nucleotidase was determined in lymphocyte plasma membranes from 14 normal subjects and 10 patients with chronic lymphocytic leukemia (CLL). Whereas the enzyme was present in the preparation from normal lymphocytes, in 7 out of 10 CLL patients the membranes had markedly decreased or no detectable 5'-nucleotidase activity. The lack of this activity from the lymphocytes of most patients with CLL constitutes an alteration in a plasma membrane enzyme from the normal cell. The presence of the enzyme in the lymphocytes of some patients with CLL and its decrease in others provide further evidence for biochemical heterogeneity among patients with this disorder.

Cell Membrane↗
PubMed1972

Purification and properties of bacteriophage T4-induced RNA ligase.

An enzyme, purified 300-fold from Escherichia coli infected with bacteriophage T4, catalyzes the conversion of 5'-termini of polyribonucleotides to internal phosphodiester bonds. The reaction requires ATP and Mg(++). For every 5'-(32)P terminus rendered resistant to alkaline phosphatase, an equal amount of AMP and PPi are formed. Various polyribonucleotides are substrates in the reaction; to date, the best substrate is [5'-(32)P]polyriboadenylate. With the latter substrate, no evidence of intermolecular reaction was obtained. However, the 5'-(32)P termini of poly(A) rendered resistant to alkaline phosphatase are also resistant to attack by RNase II, polynucleotide phosphorylase, and low concentrations of venom phosphodiesterase. Since the product formed with poly(A) lacks 3'-hydroxyl ends, as measured with these exonucleases, the enzyme appears to convert linear molecules of polyriboadenylate to a circular form by the intramolecular covalent linkage of the 5'-phosphate end to the 3'-hydroxyl terminus.

Adenosine Monophosphate↗