KC1 Extract Research Articles

Arsenic Bioaccessibility in a Soil Amended with Drinking-Water Treatment Residuals in the Presence of Phosphorus Fertilizer

A laboratory incubation study was conducted to determine the effect of drinking-water treatment residuals (WTRs) on arsenic (As) bioaccessibility and phytoavailability in a poorly As-sorbing soil contaminated with arsenical pesticides and fertilized with triple super phosphate (TSP). The Immokalee soil (a sandy spodosol with minimal As-retention capacity) was amended with 2 WTRs (Al and Fe) at 5 application rates ranging between 0% and 5% wt/wt. Sodium arsenate and TSP were used to spike the soil with 90 mg As kg(-1) and 115 mg P kg(-1), respectively. Bioaccessible As was determined at time 0 (immediately after spiking), and at 6 and 12 months of equilibration using an in vitro gastrointestinal test, and As phytoavailability was measured with a 1-M KC1 extraction test. Arsenic phytoavailability decreased immediately after spiking (20% availability at 5% rate), but only after 6 months for the Al-WTR- and the Fe-WTR-amended soil, respectively. Arsenic bioaccessibility simulated for the stomach and intestine phases showed that the Fe-WTR was more effective than the Al-WTR in resisting the harsh acidic conditions of the human stomach, thus preventing As release. Both the phytoavailable As and the bioaccessible As were significantly correlated (p < 0.001) for soil spiked with either Al- or Fe-WTR. Both WTRs were able to decrease soil As bioaccessibility irrespective of the presence or absence of P, which was added as TSP. Results indicate the potential of WTRs in immobilizing As in contaminated soils fertilized with P, thereby minimizing soil As bioaccessibility and phytoavailability.

Chemical significance of aluminium extracted from three horizons of an acid forest soil, using chloride salt solutions

SummaryAluminium is usually important in exchange reactions in acid soil, but amounts extracted are strongly affected by procedure. We examined the impact of proton release, following salt addition, on Al removal from three horizons (Oe, Oa and A12) of an acid, brown forest soil.The Al was first extracted with either 1 M KC1, 1 m NH4C1 or 0.5 m CuCl2 on the three horizons limed to pH 5.5. For any lime addition, both the pH drop following salt addition and the amounts of extracted Al were greater with CuCl2 than with KC1 or NH4C1. For the Oa and A12 horizons there was a single inverse linear relation between amount of Al extracted and the pH of final extract, independent of the extracting cation. In the Oe horizon CuCl2 extracted constant amounts of Al, whereas the quantity of Al removed by KC1 or NH4C1 increased linearly as pH declined below pH 3.6.Extra Al was mobilized following unbuffered KC1 extraction, a side effect induced by the extracting procedure itself.Al mobilization increased with increasing H+ additions. In the Oe horizon, equilibrium was established rapidly (≤ 24 h), and decreasing the pH of the soil‐KCl suspensions to 2.0 resulted in extracted Al amounts equal to or slightly greater than those obtained with CuCl2 solutions. Al amounts extracted with acidified KC1 solutions from the A12 were close to those obtained using CuCl2 solutions at similar pH in the extract. In the samples from the A12 layer, increasing the equilibration time resulted in increasing proton consumption and equivalent release of Al ions in the extract.

Comparison of ceramic suction cups and KC1 extraction for the determination of nitrate in soil

SummaryComparisons of nitrate concentrations in soil core extracts and ceramic suction cup isolates were made on a coarse sand and a sandy loam to evaluate the methods for estimating nitrate concentrations percolating through the root zone. On the coarse sand the comparisons were made at 80 cm on three dates during the winter of 1988/89. For each date, 103 soil samples and 101 or 102 suction cup isolates were taken. On the sandy loam the comparisons were made at 25 and 80 cm on two dates in March 1990. For each date and depth, 57 soil samples and 55–57 suction cup isolates were taken. On the coarse sand the mean nitrate concentrations were the same for the two methods. On the sandy loam the results obtained using the two methods differed significantly in only one of the four comparisons. However, the results indicated that the suction cup isolates differed slightly from the volume‐averaged concentrations obtained from the soil samples. The type of frequency distribution, normal or lognormal, seemed to be influenced both by the mean nitrate concentration and by the soil structure, and thus by the pattern of percolation. The size of sample required to estimate the mean nitrate concentration with a probability of 95% and a precision of 10% varied from 7 to 106.

Fractionation of extractable aluminum in acid soils: A review and a proposed procedure

Abstract Different forms of soil aluminum (Al) are involved in the retention of anions and cations, phytotoxicity of Al in acid soils, CEC reduction and soil physical properties such as aggregate stability and water infiltration. Therefore it is desirable to quantify the different forms of Al in soil especially acidic soils. A rationale was developed from a literature survey to identify the following fractions of Al: (a) exchangeable quantified by 1M KC1 extraction; (b) organic bound quantified by 0.1M CuCl2 + 0.5M KCl extraction; (c) sorhed Al extractable with 1M NE4OAc at pH 4.0; (d) amorphous Al oxide and hydroxide and amorphous aluminosilicates (if present) extractable with 0.2M ammonium oxalate at pH 3.0; and (e) interlayered Al extractable with 0. 33M sodium citrate at pH 7.3. Pools (a), (b), and (c) are extracted sequentially. Amorphous Al oxide and hydroxide (pool d) is calculated from ammonium oxalate extractable Al minus (a + b + c). Interlayered Al is calculated from sodium citrate extractable Al minus ammonium oxalate extractable Al. The latter two extractions are done on separate subsamples of soils. From preliminary studies and data for 13 soil samples it is suggested that this fractionation of soil Al is more meaningful than that obtained by the KCl ‐> K4P2O7 ‐> ammonium oxalate > citrate‐bicarbonate‐dithionite extraction sequence.

Biochemical Characterization of Casein Kinases II (CK-II) from Cultured Cells of the Liverwort, &lt;italic&gt;Marchantia polymorpha&lt;/italic&gt;

Monomeric and oligomeric forms of CK-II have been purified from a 1.0 M KC1 extract of the liverwort, Marchantia polymorpha, by means of heparin-agarose column chromatography and gel filtration on Superose 6HR (HPLC). It was found that (i) a monomeric kinase (approximately 38 kDa) is the main form of CK-II in the cells; and (ii) the enzymatic properties of oligomeric kinase (approximately 140 kDa), which cross-reacts with anti-serum against Drosophila CK-IIβ, are similar to those of CK-II (α2β2) in various animal cells.

Cell-Free Interaction of the Estrogen Receptor with Mouse Uterine Nuclear Matrix: Evidence of Saturability, Specificity, and Resistance to KC1 Extraction

An integral part of the mechanism of estrogen action is the interaction of estrogen receptor (ER) complexes with specific nuclear acceptor sites to effect alterations in genomic expression. The localization of nuclear acceptor sites has been in question, but an increasing body of indirect evidence implicates the nuclear matrix. To assess the binding characteristics of [3H]estradiol-receptor complexes (3HER) to nuclear matrix, ER from ovariectomized mice was partially purified by ammonium sulfate precipitation and incubated under cell-free conditions with mouse uterine nuclear matrix at 4 C. The binding capacity of the nuclear matrix was determined to be 36.4 +/- 5.7 fmol/100 micrograms DNA, with a Kd of 0.23 +/- 0.03 nM. Binding to nuclear matrix sites was specific, as determined by the ability of increasing concentrations of unlabeled ER complexes to inhibit binding of 3HER. Spleen, used as a nontarget tissue, contained fewer binding sites (n = 4.07 fmol/100 micrograms DNA) than matrix from liver (n = 14.2). The binding affinity was the same in all three tissues. Injection of animals with estradiol before death was associated with loss of assayable nuclear matrix binding sites, implying occupancy of sites by ER in vivo. Unbound receptor (R) also demonstrated the ability to bind to uterine matrix (n = 40.2 +/- 2.7 fmol/100 micrograms DNA; Kd = 0.26 +/- 0.05 nM) as well as to competitively inhibit the binding of 3HER complexes. However, heat-inactivated receptor displayed no binding or competing activity, nor did the progesterone receptor. The two forms of the receptor can be functionally distinguished by extraction with 0.6 M KCl; 43% of ER, but no R, were resistant to KCl extraction. These results indicate that nuclear acceptor sites are associated with the nuclear matrix. Furthermore, these sites demonstrate the criteria expected of specific binding sites, i.e. high affinity, limited capacity, hormone receptor, and relative tissue specificity. The apparent association of uncomplexed receptor to nuclear acceptor sites may explain the uterine tissue nuclear localization of ER in the absence of hormone.

Steroid receptors and histological types in cervical cancer.

AbstractEstrogen receptor (ER), progestin receptor (PR), and androgen receptor (AR) levels in cytosol, nuclear KC1 extract, and nuclear KC1 unextractable fraction were determined in 34 cases by Scatchard analyses, using the dextran‐coated charcoal (DCC) method for the first two receptors and the washing method for the last one. The dissociation constants of ER, PR and AR ranged from 10‐10 to 10‐9 M. The histological types were classified according to the World Health Organization criteria. ER, PR and AR were detected in some cases of cancer of the cervix. Regardless of the histological types of squamous cell carcinoma of the cervix, ER was detected in almost all cases. The detection rate of PR (8/27) was significantly lower (p&lt;0.03) than that of ER (25/ 27), and that of AR (16/27) tended to be lower (p&lt;0.09) than that of ER (25/27) in large cell non‐keratinizing carcinoma, keratinizing carcinoma, and small cell non‐keratinizing carcinoma. PR was not detected in cases of cervical adenocarcinoma, regardless of their histological differentiation.

Characterization and assay of progesterone-binding components in DMBA-induced rat mammary carcinoma tissue after progesterone administration

Nuclear and cytoplasmic progesterone-binding components were characterized and measured in DMBA-induced rat mammary carcinoma tissue, before and after progesterone administration. Rats, bearing growing tumors, were ovariectomized and then primed for two days with estradiol. Biopsy specimens were taken prior to or following administration of progesterone. Nuclear binding was assayed in the 0.4 M KC1 extract of the nuclear fraction using [ 3H]R5020 as ligand. The receptor character of the binding was demonstrated by: (1) high affinity ( K d ∼2nM); (2) specificity: competition by R5020 and progresterone, minimal competition by 17α-hydroxyprogesterone, corticosterone, testosterone and estradiol; (3) sedimentation constant at about 3S in a sucrose density gradient. Similar characteristics displayed the cytoplasmic receptor before and after progesterone administration. Progesterone receptor distribution in the nuclear extract and cytosol were determined in 36 tumors. The levels of total receptors (cytoplasmic plus nuclear) before and after progesterone administration varied widely, however the average values found after progesterone administration were significantly lower, 1.59 ± 0.20 pmol/mg DNA compared to 2.58 ± 0.32 pmol/mg DNA. Before progesterone administration only cytoplasmic receptors were found. One hour after progesterone administration a variable amount of the receptor (0–40%) was found in the nucleus of the tumorous tissue. In uteri of the same rats a uniform distribution of receptors (about 40% in the nucleus) was found after progesterone administration. A defect in the translocation process might be considered in the tumors with low receptors level, which suggests that DMBA-tumors may not respond uniformly to progesterone administration.

Oestrogen receptor-like binding in the surface germinal epithelium of the rat ovary.

The surface germinal epithelium of the rat ovary was isolated and grown in vitro. Cytosol from cultured cells contained a saturable component, of sedimentation coefficient 7·5–8·5S, which bound oestrogenic and antioestrogenic substances with high affinity (Kd 400 pmol/l). Nuclei isolated from cells exposed to [3H]oestradiol contained radioactivity partially susceptible to KC1 extraction. Sedimentation analysis of the KC1 extract showed that [3H]oestradiol was associated with a moiety of sedimentation coefficient 4·5–5S.

Effect of divalent cations on the binding of 3,5,3'-triiodothyronine to isolated rat liver nuclei.

During incubation of rat liver nuclei at 22 C, a fraction of the T3 receptor was released to the medium. Ca2+ and Mg2+ decreased the amount of receptor released, thereby increasing specific T3 binding to the nuclei. However, the total specific binding (i.e. in the nuclei plus the incubation medium) was decreased at concentrations of divalent cations that induced maximal inhibition of receptor release. Neither Ca2+ nor Mg2+ influenced the binding of [125I]T3 to the receptor when a KC1 extract of the nuclei was studied. Therefore, the decrease of total T3 binding when maximal amounts of receptor were chromatin bound was probably due to a decreased affinity of the chromatinbound receptor. Furthermore, in the presence of 1 mM MgCl2 50% of the receptor was released to the incubation medium, and the affinity of the solubilized receptor was 1.7 times higher than the affinity of the receptor that remained associated to the chromatin; when CaCl2 was included in the incubation medium, 91% of the receptor was in the nuclei, and its affinity was lower than the affinity of the nuclear bound receptor in the presence of 1 mM MgCl2 and no Ca2+. These results suggest that divalent cations lower the affinity of the chromatin-bound receptor. Receptor dissociation from the nuclei was studied by diluting 15 times a nuclear suspension, at 0 C for 1 h. Receptor dissociation from the nucleus was enhanced by increasing dilution volume and Na+, Ca2+, or Mg2+ concentrations. In the absence of salt, 25% of the receptor was released from the nuclei. Addition of either CaCl2 or MgC12 up to a concentration of 10 mM increased receptor loss to 50%. In the presence of 0.15 M NaCl, receptor loss was 70% in the absence of divalent cations, and in either 10 mM CaCl2 or MgCl2 it was 90%. The main conclusion from this work is that divalent cations might influence the amount of chromatin-bound T3-receptor complex in two ways: 1) by lowering the affinity of the chromatin- bound receptor for T3, and 2) by increasing the dissociation of the receptor from its chromatin acceptor sites.

Studies on the mode of action of calciferol XXXII. Evidence for a 24(R),25(OH) 2-vitamin D 3 receptor in the parathyroid gland of the rachitic chick

Summary Previous studies from a number of laboratories suggest a biological role for 24(R),25-dihydroxyvitamin D3 [24,25(OH)2D3] in bone mineralization, parathyroid hormone secretion and possibly intestinal calcium absorption. As a consequence we have initiated a search for a binding protein/receptor for 24,25(OH)2D3 analogous to that previously shown to exist in many tissues for 1,25-dihydroxyvitamin D3. Here we report for the first time the existence of a 24,25(OH)2D3 receptor/binding protein in the parathyroid glands of rachitic chicks. Incubation of a 105,000 x g supernatant of a 0.4 M KC1 extract of parathyroid gland chromatin with [3H]-24,25(OH)2D3 both before and after 5–20% sucrose density gradient centrifugation resulted in the detection of a receptor-like binding component with a mobility of 3.2–3.4 S. This putative 24,25(OH)2D3 receptor was shown to have ligand specificity for 24,25(OH)2D3 over 25-hydroxyvitamin D3 and to be a different macromolecular species than the 6 S binding protein for 25(OH)D3 which is present in the cytosol but not chromatin of the parathyroid gland.

Nuclear androgen receptors in human prostatic tissue. Extraction with heparin and estimation of the number of binding sites with different methods

A procedure for the estimation of nuclear androgen receptors in benign prostatic hyperplastic tissue is described, which employs extraction of receptors from nuclei with buffers containing heparin. Extraction of a nuclear pellet with a heparin-containing (1 g/1) buffer appeared to have definite advantages over 0.4 mol/1 KC1 extraction. Heparin appeared to be twice as efficient in extracting androgen receptors. In addition aggregated receptor proteins, formed after storage at — 80°C, were partly deaggregated by heparin. Specific isolation of the androgen receptor was performed using either agar gel electrophoresis, protamine sulphate precipitation or LH-20 gel filtration. A comparison was made between the amounts of estimated receptors with these different techniques. Protamine sulphate precipitation resulted in the highest estimates of receptor-bound 5α-[3H]dihydrotestosterone (3H-DHT). Treatment of the labelled nuclear extracts with a charcoal suspension prior to the receptor assay resulted in lower amounts of estimated androgen receptors. A method for routine evaluation of nuclear androgen receptors in prostatic tissue has been evaluated, which involves extraction of nuclear pellets with a heparin-containing (1 g/1) buffer, exchange labelling of the nuclear extracts for 20 h at 10°C and quantification of the receptors with protamine sulphate precipitation.

Use of capillary tube leukocyte adherence inhibition for the detection of tumor-specific immune responses.

The tumor-specific immune response of A/J mice was determined at various times after subcutaneous injection with a transplantable spindle-cell sarcoma (SaI) using a leukocyte adherence inhibition (LAI) assay carried out in capillary tubes. Solubilized antigens prepared by 3M KC1 extraction of the specific tumor, other transplantable tumors and normal A/J liver were used in the evaluation of LAI reactivity. The assay was found to be capable of detecting a significant antitumor response before the subcutaneous tumors became detectable by palpation. The response remained significant until the tumors were greater than 25 mm in diameter. Responsive cell populations did produce an active supernatant, indicating the possible presence of a lymphokine and/or specific cytophilic antibody.

An Androgen Receptor in the Nuclei of Late Spermatids in Testes of Male Rats*

We recently identified and characterized, by RIA of bound testosterone (T), an androgen receptor in nuclei isolated from seminiferous tubules of the male rat. By use of similar methods, we now report the presence of a similar androgen receptor in salt extracts of late spermatids from stage 12 on, which were prepared by sonication of homogenized testes or mechanically dissected seminiferous tubules and isolated on a discontinuous sucrose density gradient. Purity of the spermatid preparation was approximately 99%, as established by light microscopy. The major component of a 0.4 M KC1 extract of spermatid nuclei migrated at 4.0S on a glycerol density gradient and coeluted on hydroxylapatite with a salt extract of ventral prostatic nuclei radioactively labeled with 5α-[3H]dihydrotestosterone. In both isolation systems, there were additional minor components in the spermatid macromolecular complex, as compared to the prostatic androgen receptor. A comparison was made between the bound T concentration in late s...

The effects of injecting nitrapyrin (‘N‐serve’), carbon disulphide or trithiocarbonates, with aqueous ammonia, on yield and %N of grass

AbstractNitrapyrin and carbon disulphide (CS2), or sodium or ammonium trithiocarbonate (which evolve CS2 in soil), were injected with aqueous ammonia (NH3) into grassland in three successive seasons at Rothamsted and at Woburn, using a new site each season. Injection was done either in November (‘autumn’), or in the following February or March (‘spring’). When applied in autumn, the inhibitors increased yield and %N of grass after the mild, wet winter of 1974‐75, but had little or no effect in the two subsequent seasons. These effects are consistent with rates of nitrification of the injected NH3, estimated by KC1 extraction of soil taken from injection slits, and with winter rainfall. When inhibitors were applied in spring, yields were consistently improved at Rothamsted but depressed at Woburn. All effects were small. Nitrapyrin or CS2, injected with aqueous NH3 into grassland in autumn, reduces nitrogen losses that occur in winter. However, judging from grass yields, in these experiments (in south‐east England) losses were only a small fraction of the dose of N applied. Injecting these inhibitors with NH3 in spring can delay nitrification and increase the persistence of the injected N, but this will not necessarily increase yield.

Nuclear progesterone receptor in hamster uterus: measurement by [3H]progesterone exchange during the estrous cycle.

Previous studies with hamster uterine cytosol demonstrated a progesterone (P) receptor (Rp) that was responsive to estrogen and P action. This report describes a [3H]P exchange procedure which permits the reliable assay of nuclear Rp during the hamster estrous cycle and other experimental conditions. Nuclear Rp was extracted from uterine nuclei at 2 C using 0.5 M KC1 in Tris buffer containing glycerol. [3H]P exchange was achieved by overnight incubation of nuclear KC1 extract at 2 C. Nuclear Rp levels were obtained by Scatchard plot analysis of specific [3H]P-binding results. Nuclear Rp sedimented at 3.5S compared to 4.6S for salt-dissociated cytosol Rp in sucrose-glycerol gradients. The steroid-binding specificity of nuclear Rp was identical to that of cytosol Rp under the same ionic conditions. In vivo experiments revealed that nuclear Rp translocation was target tissue specific, hormone specific, and dependent on P dosage. A 6-h retention of nuclear Rp wasobserved in response to varying doses of P (0.1–4 mg/100 g BW). During the estrous cycle, nuclear Rp levels remained relatively constant (5–10 pmol/g tissue) on days 1–3 and increased markedly (28 pmol/g tissue) at 1600 h on day 4, coincident with preovulatory P secretion and cytosol Rp depletion. Cytosol Rp was translocated to the nuclear fraction by exogenous P treatment on all days of the cycle, but the magnitude of the nuclear Rp response was correlated with cytosol Rp availability. These results demonstrate the applicability of the [3H]P exchange assay for monitoring nuclear Rp translocation under physiological conditions.

Androgen metabolism by and binding to mature rabbit epididymal tissue: the effects of castration.

When minced epididymal tissue from intact sexually mature rabbits was incubated with 8.25 × 10 −9 M [ 3 H]-testosterone for 2 h at 0°C, followed by 1 h at 23°C, approx 10% of the unbound ether-soluble radioactivity in the cytosol was [ 3 H]-H17β-hydroxy-5α-androstan-3-one (5αDHT) and approx. 2% was [ 3 H]-5α-androstane-3α, 17β-diol (diols) and unidentified polar metabolites. Castration resulted in a decrease in 5αDHT formation. This decrease became significantly different ( P < 0.05) by 4 days postcastration. The same pattern of 5αDHT formation was observed when the incubation was conducted for 3 h at 0–4°C, except that the absolute amount and percentages of metabolites formed was reduced. Examination of binding to the slowly dissociating epididymal androgen cytoplasmic receptor indicated that the greatest amount of binding occurred 2–6 days after castration and returned to pre-castration levels by the 10th day after castration. Greater binding of androgens to the cytoplasmic receptor occurred upon incubation at 0°C than at 23°C. This was taken to indicate that nuclear translocation of the receptor-hormone complex had occurred during the 23°C incubation. Despite the post-castration induced decline in 5αDHT formation, the relative amount of 5αDHT bound to the cytoplasmic receptor remained virtually unchanged during the entire 14 day period after castration that was studied. Little radioactivity was bound to the KC1 extract of nuclei or was present in the post KCl extract nuclear debris when the minces were incubated at 0°C and most of the label present was testosterone. When the samples were incubated at 23°C, both testosterone and 5αDHT were present in the above nuclear fractions during the entire post-castration period. The time-course of maximal androgen binding to nuclei was similar to the time-course of maximal binding to the cytoplasmic receptor.

Preoperative Cell-Mediated Immune Status of Patients with Malignant Glial Tumors

The leukocyte adherence inhibition assay (LAI) was used to measure cell-mediated immunity in 26 patients with malignant glial neoplasms and in 41 control subjects. A significant inhibition of leukocyte adherence was observed in 21 out of 26 (80%) patients with malignant astrocytic gliomas in the presence of a 3M KC1 extract of glioma tissue compared to that of normal brain extract. Among the control group, no significant difference in the percentage of nonadherent leukocytes (NAL) was noted in the presence of either antigen. To study the specificity of the reaction, 3M KC1 extracts of meningioma, pituitary tumor, carcinoma of breast, carcinomas of lung, melanoma, brain, and heart tissues were employed as non-specific antigens. Such studies revealed significantly lower values of NAL. These data indicate that patients with malignant glial neoplasms manifest a cellularimmune response to glioma-associated antigens that can be measured by the tube LAI assay and that LAI assay may render additional useful information in the diagnostic and prognostic evaluation of malignant glial neoplasms.

Determination of the binding properties of estradiol-17β within the cytoplasmic and nuclear fractions of rat ventral prostate

A specific binding protein for estradiol-17β (E217β) has been detected in the cytosol of the ventral prostate of retired breeder CD strain rats. The binding protein was determined to have a sedimentation coefficient of 3.6 S by ultracentrifugation of [3H]-estradiol-17β labeled cytosol on high salt sucrose density gradients. The estrogen binding protein appears to have a greater affinity for diethylstilbestrol and estradiol-17β than for estrone or estriol. Also, the estrogen binding protein appears to be inactivated by sulfhydryl group blocking agents.The uptake of radioactivity by ventral prostate nuclei was investigated following the injection of [3H]-E2-17β in vivo. A radiolabeled protein with a sedimentation coefficient similar to the cytoplasmic estrogen binding protein was detected in the 0.6 M KC1 extract of the purified nuclei. However, in vitro studies with purified ventral prostate nuclei failed to detect a temperature dependent nuclear translocation of cytoplasmic protein-steroid complex. These studies indicate that an estrogen binding protein with some of the properties of a receptor is present in rat ventral prostate. However, the physiological significance of this protein has not been determined.

Kinetics of in vitro binding of oestradiol in subcellular fractions of testicular and uterine tissue: Characterization of oestradiol binding in testicular nuclei

1. 1. Oestradiol in rat testicular and uterine tissue is specifically bound to nuclear receptor sites, which can be separated in KCl-extractable nuclear and nuclear residual (a nuclear fraction which resists KC1 extraction) receptor sites. 2. 2. The amount of “extractable” nuclear binding sites for oestradiol in testis could be increased by mild trypsin treatment. Treatment of testicular nuclei with deoxycholate or DNAse resulted in a decrease of residual receptor sites and a concomitant increase of unbound oestradiol in the “extractable” nuclear fraction. 3. 3. The presence of KCN in vitro resulted in a relative increase in the number of oestradiol binding sites in the nuclear residual fraction in both uterine and testicular tissue; the number of binding sites in the KCl-extractable fraction was not affected by KCN. 4. 4. During in vitro incubations of testicular tissue the number of oestradiol binding sites in the KCl-extractable nuclear fraction reached a maximum and remained constant after 30min of incubation; the number of binding sites in the nuclear residual fraction decreased after incubation periods longer than 30 min. 5. 5. During in vitro incubations of uterine tissue the number of oestradiol binding sites in the KCl-extractable nuclear fraction and the nuclear residual fraction after an initial increase decreased to 50% of the maximal value between 30 and 60 min of incubation. 6. 6. It is concluded, that the testicular oestradiol receptor shows certain characteristics comparable with those of the uterine receptor. However, regarding the differences in retention time of steroids in the nucleus, it seems very unlikely that the oestradiol effect in uterus and the oestradiol effect in testis, if present, are mediated by identical receptor mechanisms.