Search PubMed⌕ Search

Biomedical subjects

A F Clark

Publications and source records attributed to A F Clark.

At least 91 records · Page 5Linked to original sources
PubMed1983

Rat prostatic acid phosphatase: androgenic control of isoelectric focusing patterns.

To further characterize the androgen dependence of prostatic acid phosphatase (AP), the isoelectric focusing patterns of enzyme activity have been examined for normal and castrated adult rats and for rats receiving androgen injections. Isoelectric focusing was performed in polyacrylamide gels over the pH range 4-8. Naphthyl phosphate was used as substrate for staining. For normal rats there was a single lysosomal band (isoelectric point(pI) = 7.35 +/- 0.04), four closely migrating secretory bands (pI = 5.96-5.63), and an androgen-dependent band (pI = 6.37 +/- 0.05) which as yet has not been identified as either lysosomal or secretory. Following castration the secretory bands decreased significantly in staining intensity, the androgen-dependent band disappeared, and two new lysosomal bands (pI's = 7.13 +/- 0.03 and 7.00 +/- 0.03) appeared. With androgen replacement the latter two bands disappeared, the androgen-dependent band reappeared, and the secretory bands increased in staining intensity but with the most anodic of the four appearing before the others. This suggests that it could be a precursor to the others. The isoelectric focusing patterns of AP activity appear to be a better method of assessing the androgen status of the prostate than are the previously used parameters, namely, enzyme specific activity, degree of inhibition by tartrate, and polyacrylamide gel electrophoretic pattern.

Acid Phosphatase↗
PubMed1983

Androgen 5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activities in ventral prostate epithelial and stromal cells from immature and mature rats.

To study androgen-mediated differentiation in the rat ventral prostate, we separated the two principal cell types (epithelial and stromal) derived from prostates of immature and mature rats on two continuous Percoll gradients. Cells were immediately placed in culture medium. Testosterone metabolism by the two prostatic cell types was evaluated using [3H]testosterone and quantifying the formation of 5 alpha-[3H]dihydrotestosterone (5 alpha-DHT) and 5 alpha-[3H]androstane-(3 alpha or 3 beta), 17 beta-diols. In epithelial cells from both immature and mature rat prostates the major testosterone metabolites were 5 alpha-DHT and 5 alpha-androstane-3 alpha, 17 beta-diol. Stromal cells metabolized less testosterone than did the epithelial cells. Differences in the relative levels of the various metabolites were observed for the two age groups. To examine in more detail the changes in testosterone metabolism observed in vitro both types of cells and unfractionated cells from immature and mature rat prostates were assayed for testosterone 5 alpha-reductase (using testosterone as substrate) and 3 alpha-hydroxysteroid dehydrogenase (using 5 alpha-DHT as substrate) activities (expressed as pmol substrate reduced/min per 10(6) cells). In immature rats both 5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activities were localized in the epithelial cell fraction (17 and 52 respectively); stromal cells showed lower 5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activity (4 and 4). Relative to epithelial cells from immature rats epithelial cells from mature rats showed a decrease in 5 alpha-reductase (7) and an increase in 3 alpha-hydroxysteroid dehydrogenase (160) activity while stromal 5 alpha-reductase showed little change (3) and 3 alpha-hydroxysteroid dehydrogenase increased to 22.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed1982

Proton nuclear magnetic resonance spectroscopy and ligand binding dynamics of the Escherichia coli L-arabinose binding protein.

The L-arabinose binding protein (ABP) from Escherichia coli was studied by proton nuclear magnetic resonance spectroscopy (1H NMR). Distinct spectral changes occur when ABP binds its natural ligand, L-arabinose, which involve resonances in the aromatic ring current shifted methyl, bulk methyl, methylene, aromatic, and amide proton regions of the spectra. Several amide resonances can be "protected" from deuterium exchange if L-arabinose is bound to ABP prior to deuterium oxide dialysis. On the basis of the pH dependence of their chemical shifts, two low-field resonances have been tentatively assigned to C2 protons of two of the three histidines present in ABP. These histidyl residues have pK values of 8.0 and 8.6 which support their involvement in ionic interactions observed earlier in the crystallographic analysis. One histidyl residue shows a small chemical shift change upon the addition of arabinose. When ABP binds D-galactose, changes in the spectra occur which are different than those observed when L-arabinose is bound. Binding of L-arabinose and D-galactose to the binding protein (ABP) was considered by equilibrium binding and fluorescence emission spectroscopy. ABP binds L-arabinose and D-galactose with high affinities (Kd's at 6 degrees C of 1.3 x 10(-7) and 1.9 x 10(-7) M, respectively), and both enthalpy and entropy contribute to the ABP-ligand association. When excited at 285 nm, ABP has a fluorescence emission maximum of 340 nm which is quenched and blue shifted (to 337 nm) upon binding L-arabinose. ABP binding D-galactose produced a similar emission shift but no fluorescence quenching.

Bacterial Proteins↗
PubMed1982

Ubiquitous nonimmunoglobulin p-azobenzenearsonate-binding molecules from lymphoid cells.

A ubiquitous nonimmunoglobulin molecule that binds p-azobenzenearsonate (ABA) has been detected in the cytoplasm of several murine cell lines, including T cell hybridomas as well as in normal liver and spleen. Similar to many recently described antigen-specific T cell factors, this ABA-binding protein has a 62,000 mol wt, and, when analyzed by direct binding, the molecule reacts with several different rabbit anti-idiotypic antisera specific to the ABA system. The presence of this antigen-specific, "idiotype positive" molecule in many different cells indicates that it is not an important immunoregulatory molecule.

Animals↗
PubMed1982

Binding of testosterone, 5 alpha-dihydrotestosterone and 5 alpha-androstane (3 alpha- and 3 beta-), 17 beta-diols to serum proteins in the rat.

Experiments with polyacrylamide gel electrophoresis at steady state conditions, indicated that testosterone, 5 alpha-dihydrotestosterone, 3 alpha-androstanediol and 3-beta-androstanediol bound only to albumin in rat serum. The extent of binding of several C19-steroids to serum proteins was measured in rat blood utilizing equilibrium dialysis. The values for the adult male rat were as follows (mean +/- SEM): testosterone 78.3 +/- 0.4% 5 alpha-dihydrotestosterone 81.8 +/- 0.4%, 3 alpha-androstanediol 95.5 +/- 0.1%; 3 beta-androstanediol 95.2 +/- 0.1%. The values for the latter two are significantly higher than those for the first two which in turn differ significantly from each other. The values for adult female and castrated male serum samples were not significantly different from those of the normal male. The results obtained for the extent of binding of C19-steroids in a 5-g% albumin solution (which is similar to male rat serum albumin concentration) did not differ significantly from values for serum indicating that the binding in the latter is due primarily to albumin. The KA's for C19-steroid binding to albumin were: testosterone 2.22 X 10(4)l/mol; 5 alpha-dihydrotestosterone 3.46 X 10(4)l/mol; 3 alpha-androstanediol 1.36 X 10(5)l/Mol and 3 beta-androstanediol 1.20 XC 10(5)l/mol. When correlated to our previously reported metabolic clearance rats (MCR) it was concluded that binding to serum proteins does not account for the significant difference between the MCR for testosterone and 5 alpha-dihydrotestosterone but may account for the lower MCR's for the 3 alpha- and 3 beta-androstanediols.

Androstane-3,17-diol↗
PubMed1982

The role of androgen metabolism in the control of androgen action in the rat prostate.

Recent results from a number of laboratories have led us to re-examine the role of 3 beta-androstanediol in the rat ventral prostate. Whereas previously 5 alpha-dihydrotestosterone and 3-beta androstanediol were thought to have distinctly separate effects on the prostate, we suggest that 3 beta-androstanediol serves only as an intermediate in the metabolism and removal of 5 alpha-dihydrotestosterone from the organ. In our view the action of androgens on the prostate are exerted exclusively through the binding of 5 alpha-dihydrotestosterone to the androgen receptor and its subsequent translocation to the nucleus. Differences in effects are related to the amount of 5 alpha-dihydrotestosterone available to the gland. 3 alpha-Hydroxysteroid dehydrogenase may play a critical role in modulating the level of 5 alpha-dihydrotestosterone available to the translocatable receptor.

3-Hydroxysteroid Dehydrogenases↗
PubMed1982

Delta 5-androstenediol: kinetics of metabolism and binding to plasma proteins in normal post-menopausal women.

Delta 5-androstenediol (delta 5-diol) while having minimal androgenic activity is of potential biological importance because it binds to oestrogen receptors and has oestrogenic activity in several systems. We have examined delta 5-diol metabolism in post-menopausal women utilizing the constant infusion technique. The metabolic clearance rate for 11 subjects was 763 +/- 50 1/24 h or 467 +/- 30 1/m2/24 h. Labelled dehydroepiandrosterone, testosterone, delta 4-androstenedione, androsterone and the sulphates of delta 5-diol, dehydroepiandrosterone and androsterone were found in the plasma. Of all the kinetic parameters only the conversion ratio for dehydroepiandrosterone sulphate was different from that for young women (4.958 +/- 0.410 for young women vs 3.084 +/- 0.220 for older women). The plasma concentration of delta 5-diol was 0.94 +/- 0.19 ng/ml and the calculated blood production rate was 686 +/- 80 micrograms/24 h. The per cent free plasma delta 5-diol was 4.6 +/- 0.25. These values are slightly lower but not significantly different from those previously reported for normal young women.

Aged↗
PubMed1982

Age-associated changes in acid phosphatase characteristics in rat ventral prostate and other organs.

Certain characteristics of acid phosphatase in the adult male rat are under androgenic control. In further investigations of this control, (1) the polyacrylamide gel electrophoretic pattern of enzyme activity, (2) enzyme specific activity, and (3) the extent of inhibition of enzyme activity by 1-tartrate were examined for prostate, seminal vesicles, kidney, liver and testes from immature, maturing, young, and old mature adult rats. On gel electrophoresis, lysosomal acid phosphatase activity was found for all tissues from all groups of animals. Secretory enzyme was found for the prostate gland, but only after maturation (it appeared between days 28 and 35). At the same time the percent inhibition of activity by tartrate decreases. For the other tissues, the percent inhibition by tartrate increases for the liver and seminal vesicles but not for the kidney and testes. These changes may reflect alterations in lysosomal enzyme characteristics and can be related to known changes in androgen production throughout the life span of the rat.

Acid Phosphatase↗
PubMed1982

Effects of aminoglutethimide on delta 5-androstenediol metabolism in postmenopausal women with breast cancer.

delta-5-Androstene-3 beta, 17 beta-diol has potential estrogenic activity because it is known to bind to receptors and translocate to the nucleus of certain estrogen target tissues. Its role in the biology of breast cancer is unclear. Aminoglutethimide plus hydrocortisone ("medical adrenalectomy") has been used to treat postmenopausal women with metastatic breast cancer. We studied delta 5-androstene-3 beta, 17 beta-diol metabolism in postmenopausal women with breast cancer before and during aminoglutethimide-plus-hydrocortisone therapy, utilizing the constant infusion technique. The metabolic clearance rate for five subjects was 799 +/- 89 liters/24 hr (470 +/- 47 liters/24 hr/sq m) before and 751 +/- 93 liters/24 hr (444 +/- 57 liters/24 hr/sq m) during therapy. Plasma delta 5-androstene-3 beta, 17 beta-diol and delta 5-androstene-3 beta, 17 beta-diol free index decreased despite absence of change in the metabolic clearance rate. Increased dehydroepiandrosterone/delta 5-androstene-3 beta, 17 beta-diol conversion ratios in individual patients suggested an increase in 17 beta-hydroxysteroid dehydrogenase activity during therapy. There were no alterations in the formation of the estrogen precursors testosterone and delta 4-androstene-3,17-dione.

Adenocarcinoma↗
PubMed1982

Glucocorticoid-induced alterations in the rabbit heart.

Daily intramuscular injection of the synthetic glucocorticoid, betamethasone, into rabbits for 2 weeks resulted in both gross and microscopic alteration of cardiac muscle. A 30 per cent increase in heart weight was based on increased muscle fiber size occasioned by the deposition of fibrillo-granular material (not glycogen in nature) in the cytosol. At the same time, some myocytes underwent profound myolysis, predominantly at the nuclear poles, occasionally pervading the entire cell. Conventional lysosomes were not increased in number or size, but certain cells possessed prominent cytoplasmic vacuoles that sometimes contained mitochondria. The biochemical basis for these cardiac changes is undetermined, but the obvious ultrastructural damage produced by betamethasone, particularly dissolution of myofibrils, may prove to have clinical significance.

Animals↗
PubMed1981

The insect brain (Na+ + K+)-ATPase. Binding of ouabain in the hawk moth, Manduca sexta.

(1) A quantitative study has been made of the binding of ouabain to the (Na+ + K+)-ATPase in homogenates prepared from brain tissue of the hawk moth, Manduca sexta. The results have been compared to those obtained in bovine brain microsomes. (2) The insect brain (Na+ + K+)-ATPase will bind ouabain either in the presence of Mg2+ and Pi, ('Mg2+, Pi' conditions) or in the presence of Na+, Mg2+, and an adenine nucleotide ('nucleotide' conditions) as is the case for the bovine brain (Na+ + K+)-ATPase. The binding conditions did not alter the total number of receptor sites measured at high ouabain concentrations in either tissue. (3) Potassium ion decreases the affinity (increases the KD) of ouabain to the M. sexta brain (Na+ + K+)-ATPase under both binding conditions. However, ouabain binding is more sensitive to K+ inhibition under the nucleotide conditions. In bovine brain ouabain binding is equally sensitive to K+ inhibition under both conditions. (4) The enzyme-ouabain complex has a rate of dissociation that is 10-fold faster in the M. sexta preparation than in the bovine brain preparation. Because of this, the M. sexta (Na+ + K+)-ATPase has a higher KD for ouabain binding and is less sensitive to inhibition by ouabain than the bovine brain enzyme. (5) This data supports the hypothesis that two different conformational states of the M. sexta (Na+ + K+)-ATPase can bind ouabain.

Animals↗
PubMed1981

Estradiol receptor levels in human breast carcinomas.

The presence or absence of a specific estradiol-binding protein receptor in the cytoplasm of primary and secondary tumour cells has been used by physicians as an important guide in deciding whether to use hormonal therapy for patients with metastatic breast cancer. This report gives the levels of estradiol receptors in the cytosol of 228 primary and secondary breast tumours, measured by a sensitive multiple-point assay in which dextran-coated charcoal separated bound form unbound estrogen. The data were analysed with a Scatchard plot. Of the 175 primary and 53 secondary tumours 53% and 32% respectively gave positive results. The mean receptor level in the primary tumours was significantly higher among older patients and increased with age. With metastatic lesions positive results were more common in lymph node samples tha in skin nodule samples.

Adult↗
PubMed1981

Small doses of 5 alpha-dihydrotestosterone mimic the effects of 5 alpha-androstane-3 beta, 17 beta-diol on acid phosphatase activity in the adult rat prostate gland.

These studies were designed to further investigate whether 5 alpha-androstane-3 beta, 17 beta-diol was exerting unique effects on rat prostate acid phosphatase activity or could possibly be exerting its actions by a small peripheral conversion to 5 alpha-dihydrotestosterone. Intraperitoneal administration of 5 alpha-dihydrotestosterone in doses of 1 mg, 100 microgram or 50 microgram per day starting 7 days after castration led to the restoration of normal characteristics of acid phosphatase activity. However, when 5 alpha-dihydrotestosterone was given in a dose of only 25 microgram per day starting 7 days after castration, the changes in acid phosphatase activity were indistinguishable from those found when 5 alpha-androstane-3 beta, 17 beta-diol was administered in a dose of 2 mg per day. This suggests that the effects of 5 alpha-androstane-3 beta, 17 beta-diol can be explained by its conversion to small amounts of 5 alpha-dihydrotestosterone.

Acid Phosphatase↗
PubMed1981

Na+ + K+-ATPase in serially excised segments of epileptic monkey cortex.

The membrane-bound enzyme Na+ + K+-ATPase was measured in serially excised specimens of cerebral cortex in epileptic and control monkeys. Experimental chronic epileptic cortex showed significantly lower values than controls, as is seen in some other models and human epilepsy, but is different from the increased enzyme values in cobalt and freezing lesion epilepsy.

Aluminum Hydroxide↗
PubMed1981

High-affinity arabinose transport mutants of Escherichia coli: isolation and gene location.

The gene araF, the product of which is the L-arabinose-binding protein--a component of the high-affinity L-arabinose transport system, was located on the Escherichia coli linkage map at 45 min. We established this location using bacteriophage P2 eductates and bacteriophage P1 cotransduction frequencies with the adjacent genetic loci, his (histidine biosynthesis) and mgl (methylgalactoside transport). In addition, we isolated a number of mutants that phenotypically exhibited altered high-affinity L-arabinose transport capacities. At least two of these mutations were located in the araF gene, as binding protein purified from these strains exhibited altered in vitro arabinose-binding properties.

Arabinose↗
PubMed1981

Plasma concentrations of C-19 steroids, estrogens, FSH, LH and prolactin in post-menopausal women with an without breast cancer.

The plasma levels of 5 alpha-dihydrotestosterone, testosterone, delta 5-androstene-3 beta-17 beta-diol, delta 4-androstenedione, dehydroepiandrosterone, estrone, estradiol, dehydroepiandrosterone sulfate, follicle stimulating hormone, luteinizing hormone and prolactin were measured in normal post-menopausal women and in post-menopausal women with proven breast cancer. The mean prolactin level was significantly higher (p less than 0.01) and the mean 5 alpha-dihydrotestosterone level lower (p less than 0.05) for the women the breast cancer. There were no significant differences for any of the other hormones. As well, there were no significant differences for the extent of binding of testosterone and delta 5-androstene-3 beta, 17 beta-diol to plasma proteins between the two groups of subjects.

Aged↗
PubMed1980

Mg2+ inhibition of Na2+-stimulated Ca2+ release from brain mitochondria.

Magnesium has been shown to modulate the Na+-stimulated release of Ca2+ (Na/Ca exchange) from brain mitochondria. The presence of 5 mM MgCl2 extramitochondrially inhibits the Na/Ca exchange as much as 70%. Additionally, Na+-stimulated Ca2+ release is enhanced by the presence of divalent chelators, this stimulation also being inhibited by the addition of excess Mg2+. The inhibitory effect of Mg2+ and the enhancement by chelating agents were both reversible. Heart mitochondria exhibit a similar enhancement of Na/Ca exchange by chelators and inhibition by MgCl2, though not as pronounced.

Animals↗