Biomedical subjects
Publications and source records attributed to C Bonne.
gamma-Glutamyl transpeptidase catalyzes the initial step in the utilization of glutathione. In the lens, this enzyme is accessible to externally supplied substrates. An efflux of glutathione from the lens occurs when it was incubated in saline. Inhibition of gamma-glutamyl-transpeptidase by L-serine-borate decreases the rate of glutathione breakdown in the external medium and the rate of its decline in the lens.
Metabolism of sodium (14C)-arachidonate by bovine epithelial lens cells was studied in culture. The cells converted arachidonic acid into a major product whose formation was not inhibited by aspirin, a cyclo-oxygenase inhibitor, but was suppressed by nordihydroguaiaretic acid, a lipoxygenase inhibitor and by dexamethasone. This metabolite co-migrated with leukotriene B4 in thin layer chromatography and high pressure liquid chromatography. These data represent the first evidence for a lipoxygenase product in the lens. LTB4 could play an important role in the physiopathology of this organ.
Explore the source record for details and available documents.
The rat liver single-stranded DNA binding protein, S25 and HD25, isolated by differential DNA cellulose affinity chromatography was compared to the high mobility group proteins, HMG1 and HMG2, isolated from rat liver chromatin by the technique of Goodwin et al. (Goodwin, G. H., Sanders, C., and Johns, E. W. (1973) Eur. J. Biochem. 38, 14-19). Analysis of their amino acid composition, electrophoretic mobility, and tryptic peptide map reveal the identity of the single-stranded DNA binding protein with HMG1 protein, implying that the rat liver HMG1 protein becomes able both to destabilize a double helix of DNA and to stimulate homologous DNA polymerases only when rat liver cells enter a phase of DNA synthesis, possibly after a specific modification.
Incubation of rat liver single-strand DNA binding protein S25 with covalently closed relaxed SV40 DNA in the presence of rat liver topoisomerase I induced a decrease in the linking number LK of DNA, so that it appeared negatively supertwisted after removal of the protein. delta LK was found to be a linear function of protein to DNA ratio and reached a plateau corresponding to about 15 superhelical turns. The same result was obtained when S25 was incubated with form I or form Ir before addition of topoisomerase I or when SV40 was replaced by PM2 DNA. The observed reduction in the linking number of DNA when it is closed in the presence of rat liver protein S25 can be explained either by supercoiling of DNA induced by S25 or by detorsion or unwinding of DNA.
As shown by competition experiments, the single-strand DNA binding protein from normal rat liver (S25) interacts preferentially with supercoiled DNA compared to relaxed DNA duplexes. When followed both by sedimentation analysis and by nitrocellulose filter assay, the binding of S25 to SV40 supercoiled DNA (FI) appears to be non-cooperative. Saturation is reached at a protein to DNA weight ratio of about 2. The S25-DNA complexes prefixed with glutaraldehyde appear as beaded structures having an average of 14 to 16 beads per SV40 DNA molecules. Cross-linking of S25 bound to SV40 DNA by dimethyl suberimidate allows to detect oligomeric structures containing a maximum of twenty monomers of S25. When complexes are treated by glutaraldehyde, 10% of the genome become resistant against micrococcal nuclease. Moreover, S25 affects the DNA helical structure. Superhelical forms are generated by the association of S25 with SV40 DNA, in the presence of nicking-closing enzyme.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The costovertebral organs [CVO] and seminel vesicles [SV] of the hamster exhibit high saturable androgen uptake. The physicochemcal characteristics of the cytoplasmic androgen receptor present in these tissues have been determined and compared to those obtained in rat prostate[P]. Using the synthetic androgen R 1881 [methyltrienolone] as a radioactive ligand, it has been shown that the affinity of this compound for the cytosol CVO receptor [Kd = 0.7 +/- 0.1 nM] is similar to that for the crytosol SV receptor [Kd = 2.4 +/- 0.9 nm] in hamsters and the cytosol P receptor [Kd = 0.6 +/- 0.1 nM] in rats. The hormonal specificity of binding in these tissues is restricted to androgens. Moreover, testosterone and dihydrotestosterone have the same relative binding affinity in CVO and SV compared to R 1881. Following castration, the total number of androgen sites, as measured by an exchange assay with R 1881, decreases rapidly and parallels with a fall in lipogenic activity. Administration of an androgen rapidly restores binding capacity.
Cytosol androgen receptor was assayed in 18 human skin biopsies by an exchange technique with a labelled potent synthetic androgen, methyltrienolone (R 1881), under conditions which measured total (i.e. both free and occupied) binding sites. Androgen binding sites were only present in skin biopsies from patients with marked seborrhoea often accompanied by acne (8 cases) and no sites were detected in normal skin biopsies (7 cases). Three biopsies from seborrhoeic patients, however, did not contain androgen receptor. Although no direct quantitative correlation could be drawn between binding site concentration and sebum excretion, it would seem that the androgen receptor content nevertheless constitutes an important parameter in the study of the hormonal control of seborrhoea.
Methyltrienolone (R 1881 - 17beta-hydroxy-17alpha-methyl-estra-4, 9, 11-trien-3-one) binding to rat ventral prostate cytosol has a specificity typical of an androgen receptor. In human benign prostatic hypertrophy (BPH) tissue, the specificity of [3H] R 1881 binding is different from that measured in rat prostate: progesterone and R 5020 (17, 21-dimethyl-19-nor-4, 9-pregnadiene-3, 20-dione) being more potent while 19-nortestosterone is less potent competitor. Moreover, the synthetic progestin [3H] R 5020 binds to BPH tissue with a similar specificity. These data suggest the presence of progestin binding components or of an atypical androgen receptor in human BPH cytosol.
Methyltrienolone (R 1881 - 17beta-hydroxy-17alpha-methyl-estra-4,9,11-trien-3-one) binds specifically to androgen receptor in rat prostate cytosol where, unlike androstanolone, it is not metabolized. By exchanging bound endogenous hormone in rat prostate cytosol with labelled R 1881, it is possible to measure total (free anc occupied) binding sites. This assay method has also been applied to the measurement of androgen receptor sites in human benign prostatic hypertrophy where R 1881 has the added advantage of not being bound by any contaminating plasma protein (sex hormone binding protein).
The binding of methyltrienolone (R 1881) in crude human hyperplastic prostate cytosol was determined by a charcoal assay. Maximum binding was observed after 2-3 h of incubation at 0 degrees C. This binding decreased steadily thereafter and reached 41% of the 2-hour values after 96 h of incubation. In human hyperplastic prostate, the binding of 3H-R 1881 was competed by low concentrations of R 1881, R 5020 and progesterone and by high concentrations of dihydrotestosterone (DHT) and 17 alpha-methyl-DHT. In the rat prostate, on the other hand, this binding was competed by low concentrations of DHT and 17 alpha-methyl-DHT and only by high concentrations of progesterone and R 5020. The apparent association constant (Ka) of R 1881 was determined in three human prostates and found to be 0.2-0.4 X 10(9) liters/mol; the number of binding sites ranged from 101 to 158 fmol per mg of protein. These findings constitute further evidence for the existence of relatively large amounts of a progesterone-binding component in human hyperplastic prostate.
Explore the source record for details and available documents.
Methyltrienolone (R 1881), 17beta-hydroxy-17alpha-methyl-estra-4,9,11-trien-3-one, a very active androgen, binds specifically to rat prostate cytosol with a higher affinity than androstanolone. Unlike the physiological hormone, however, it is not bound by human sex steroid plasma binding protein, SBP. This specific ligand is thus a useful tool for the detection of elusive androgen receptors and for their study, for instance, in human tumors where interference from plasma contamination has to be circumvented.
Explore the source record for details and available documents.