Alfven waves in the solar corona.

Alfvén waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun's corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfvén waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy.

Androgen receptor in rat liver: characterization and separation from a male-specific estrogen-binding protein.

Many liver processes are sexually dimorphic. In particular, the microsomal content of specific enzymes and the synthesis of specific proteins are under sex steroid hormone control. Because the liver of male rats is strikingly androgen responsive, we sought evidence for an androgen receptor in this tissue. We detected and characterized both cytosolic and nuclear androgen-binding proteins. Both forms bind [3H]R1881 (methyltrienolone, 17 beta-hydroxy-17 alpha-methyl-4,9,11-estratriene-3-one) with the high affinity, low capacity, and specificity for androgens and antiandrogens characteristic of androgen receptors. No high-affinity binding of [3H]DHT could be detected in unfractionated cytosol because of the rapid metabolism of this ligand; however, binding of a DHT metabolite to the high-capacity male-specific estrogen binder (MEB) of cytosol was observed. Both gel filtration and heparin-Sepharose affinity chromatography separate the cytosolic androgen receptor from MEB. Incubation of cytosol in the absence of sodium molybdate resulted in androgen-binding activity which was retained by DNA-cellulose. Castration of male rats results in a time-dependent loss of both cytosolic and nuclear androgen binding, as well as a loss in MEB activity. Androgen-binding activity is low in livers from female rats, but can be induced by testosterone treatment. An intact pituitary is necessary for maintenance of androgen-binding activity, as hypophysectomy results in complete loss of activity.

Effects of H2-antagonists on androgen imprinting of male hepatic functions.

Many of the sex-differentiated functions of the liver of adult male rats depend upon the occurrence of neonatal androgen imprinting, a brief surge of androgen early in life. We investigated whether androgen imprinting is necessary for the development and maintenance of levels of a microsomal enzyme, estrogen-2-hydroxylase (E-20Hase), and a male-specific cytosolic estrogen binder (MEB) which are higher in adult male than in adult female rats. Cimetidine, a weakly antiandrogenic H2 blocker, was administered to pregnant and lactating rats from day 12 of gestation through weaning on day 21. Livers of male progeny, 120-150 days of age, were assayed for E-2OHase and MEB activity; a maternal dose equivalent to 2.5 times the usual human dose inhibited MEB activity in the levels of the offspring by 40% but had no effect on E-2OHase. However, a higher dose (5 times the human dose) was effective in reducing the E-2OHase activity by 50%. Rats whose mothers had received either no drug or an equivalent dose of ranitidine, another H2 blocker without antiandrogenic activity, were used as controls. The groups were not different in hepatic cytosolic androgen receptor content, body weight, or serum testosterone. In other studies, the requirement of neonatal androgen imprinting for full expression of adult levels of MEB and E-2OHase was determined. Female rats, which have low levels of E-2OHase and undetectable levels of MEB, were given androgen on day 1, on day 60 after ovariectomy, or at both times. Levels of E-2OHase equivalent to those in adult males were induced in females receiving both androgen treatments, whereas either treatment alone induced E-2OHase to the level of that in males castrated at adulthood or neonatally, which is about 50% that in normal male controls. In addition, MEB levels were induced in females to 85% of that in normal males by both androgen treatments and to 50% by administration of androgen to adult females or to adult males castrated neonatally. Administration of androgen to females during the neonatal period only did not induce MEB. We conclude that both MEB and E-2OHase require androgen imprinting for full expression in adult male rats.

Binding of activated progesterone receptor to microsomes.

Specific binding of steroid hormones to microsomes has been reported for several tissues. In the hen oviduct, this receptor appears to be very similar to activated cytosolic receptor. The microsomal receptor is readily solubilized, and resembles the cytosolic receptor in all physico-chemical characteristics: sedimentation coefficient approximately 4 S, Stokes radius 5.5 nm, slow dissociation rate of the complex, adsorption to polyanions. It is precipitated by an antibody to the cytosolic receptor. Microsomes display saturable binding of cytosolic receptor, with a Bmax of approximately 300 fmol/mg protein. This binding is also observed using microsomes from non-target tissues, and is decreased by treatment with RNase. It seems likely that microsomal binding is due to the high affinity of activated cytosolic receptor for RNA.

Inhibition of iron-sulfur protein-mediated reduction of cytochrome P-450SCC by specific antibodies.

The mechanism of inhibition of cholesterol side-chain cleavage by specific antibodies was studied systematically. The antibodies had no effect on substrate binding as determined by optical spectroscopy or on the heme environment of the cytochrome P-450 insofar as was detectable by electron paramagnetic resonance spectroscopy. They did not bind to either iron-sulfur protein or its reductase. The antibodies had no effect on chemical reduction of the P-450 or on P-450-CO complex formation. They did inhibit the NADPH-dependent reduction of P-450 and subsequent formation of the P-450-CO complex. This inhibitory effect was concentration dependent and was correlated with the inhibitory effect of the antibodies on enzymatic cholesterol side-chain cleavage. Similar results were obtained using Fab fragments. These results indicate that the antibodies inhibit side-chain cleavage by binding to a region close to the iron-sulfur protein-binding site, thereby preventing transfer of reducing electrons to the cytochrome P-450.

The effect of exposure to charcoal and ion-exchange chromatography on the dissociation rate of estrogen from the nuclear estrogen receptor of hen oviduct.

The method of initiating dissociation of 3H-estradiol from the nuclear estrogen receptor of hen oviduct was found to have a profound effect on the dissociation rate. Likewise, prior exposure to charcoal or partial purification by ion-exchange chromatography had an effect on the dissociation rate. When the reaction was initiated by isotopic dilution with the addition of 1 microM unlabeled estradiol, dissociation of the complexes was rapid (t 1/2 approximately 3 min). When the reaction was initiated by the addition of charcoal to adsorb free steroid, the dissociation of the complexes proceeded slowly (t 1/2 approximately 30 min). Partial purification of the receptors by DEAE-Sephacel chromatography or 15 min exposure to charcoal at 0 degree C prior to initiation of the dissociation reaction by isotopic dilution produced a form of the receptor that exhibited an intermediate dissociation rate (t 1/2 approximately 10 min). The partially purified receptor that exhibited an intermediate dissociation rate was reconverted to the rapidly dissociating form in a reconstitution experiment. These data raise the possibility of a nuclear substance that regulates the rates of estrogen dissociation.

Characterization of the estrogen receptor extracted from hen oviduct nuclei with pyridoxal phosphate.

The estrogen receptor was extracted in high yield from nuclei of laying hen oviduct with 10 mM pyridoxal-5'-phosphate (PLP). The receptor extracted under these conditions, unlike that extracted with 0.4 M KCl, displayed no tendency to aggregate on sucrose gradients in low salt. The receptor was eluted as a single peak from DEAE-Sephacel at an ionic strength of 0.13 M KCl. The receptor after DEAE chromatography had approximately half the molecular weight of that in the nuclear extract. A larger form could be reconstituted by the addition of whole nuclear extract to the DEAE eluate. These data support the notion that the nuclear estrogen receptor is a dimer composed of similar subunits.

Transformation of a rabbit progesterone receptor from an 8S form to 5.5S and 4S forms.

The 8S form of the rabbit uterine progesterone receptor transforms slowly at 0 degree C to a 4S form with an intermediate 5.5S form. The transformation is accelerated by either heat, increased ionic strength and dilution of cytosol. The transformation, which is reversibly inhibited by sodium molybdate, is unrelated to total cytosolic alkaline phosphatase activity. The transformation is accompanied by a positive change in receptor surface charge and a decrease in the rate of progesterone dissociation. The stability of the 8S progesterone-receptor complex is reduced and the sedimentation coefficient increased by acidic conditions; acid does not affect the 4S receptor as drastically.

Temperature dependence of the dissociation rate constants for the nonactivated (molybdate-stabilized) and activated progesterone receptor-hormone complexes from the chick oviduct.

Both the nonactivated and activated forms of the chick oviduct cytosol progesterone receptor-hormone complexes displayed first-order dissociation kinetics at temperatures between 0 and 25 degrees C. The rate constant was always 2-3-times greater for the nonactivated than for the activated complex. The thermodynamic parameters calculated from the Eyring plot for the nonactivated and activated forms, respectively, were: delta H+ = 28.6 +/- 0.2 and 29.9 +/- 1.5 kcal/mol; -T delta S+ = 7.4 +/- 0.6 and 7.7 +/- 1.6 kcal/mol; and delta G+ = 21.3 +/- 0.5 and 22.1 +/- 0.1 kcal/mol. These values suggest that activation results in an increase in enthalpy of the ligand-receptor interaction, thus stabilizing the complex. The dissociation rate constants for the native complex obtained by two different experimental approaches, namely, isotope dilution ('chase') and dissociation against charcoal, indicated the absence of cooperativity in the receptor-ligand binding.

Molecular interactions of progesterone analogues with rabbit uterine cytoplasmic receptor.

Binding energies of progesterone analogues with single modifications were calculated from their affinities for the cytosolic receptor of rabbit uteri. The effects of individual substituents were analyzed in terms of hydrogen bonds, van der Waals' forces, and hydrophobic interactions. Binding to the receptor is attributed to hydrogen bonds involving the ketones at carbons 3 and 20, and van der Waals' interactions at carbons 2, 4, 7, 9, 12, 18, and 19 at which positions the separation of the steroid from the receptor appears to be about 0.1 nm or less. Greater separation occurs at carbons 6, 11, 14, 15, 16, and 21. The receptor probably has a hydrogen acceptor approximating the 11 beta position of the bound steroid. The enthalpy of binding of the progesterone molecule is about 26 kcal/mol but on the basis that the two hydrogen bonds contribute about 6 kcal/mol and each of the van der Waals' attractions about 1 kcal/mol, the sum of the individual bonds totals only about 20 kcal/mol. The difference of 6 kcal/mol is attributed to intrareceptor bonds that are established after a change in receptor conformation is initiated by progesterone binding. This change in conformation fixes the steroid in its protein niche and retards dissociation. We speculate that this alteration in conformation is related to "activation" and possibly other functions of the complex.

Temperature dependence of kinetic interactions between progesterone and the uterine cytoplasmic receptor.

The temperature dependence of the rates of dissociation and association for progesterone-receptor interactions was measured over the temperature range of 0-20 degrees C. The dissociation process is biphasic indicating that either two forms of receptor are present or that the binding of progesterone to the receptor is a concatenated reaction. The enthalpy of activation for the dissociation of progesterone from the receptor is about 26-28 kcal/mol and the entropic energy of activation is about -5 kcal/mol. The enthalpy of activation for the association of these molecules is about 3 kcal/mol and the entropic energy of activation is about 6 kcal/mol. These data are consistent with a model of progesterone binding to the receptor that includes hydrogen bonds between each of the two ketone groups and hydrogen donors on the receptor protein and involves van der Waals' interactions, due to the close proximity of the receptor binding site to a large fraction of the progesterone surface.