Separation of solubilized alpha and beta adrenergic receptors by affinity chromatography

Oxidative damage of DNA by chromium(V) complexes: relative importance of base versus sugar oxidation

Chromium(V)-mediated oxidative damage of deoxy-ribonucleic acids was investigated at neutral pH in aqueous solution by utilizing bis(2-ethyl-2-hydroxy-butanato)oxochromate(V) (I) and bis(hydroxyethyl)-amino-tris(hydroxymethyl)methane)oxochromate(V) (II). Single-stranded and double-stranded (ds) calf thymus and human placenta DNA, as well as two oligomers, 5'-GATCTAGTAGGAGGACAAATAGTGTTTG-3' and 5'-GATCCAAGCAAACACTATTTGTCCTCCTACTA-3', were reacted with the chromium(V) complexes. Most products were separated and characterized by chroma-tographic and spectroscopic methods. Polyacrylamide gel electrophoresis experiments reveal more damage at G sites in comparison to other bases. Three primary oxidation products, 5-methylene-2-furanone (5-MF), furfural and 8-oxo-2'-deoxyguanosine, were characterized. A minor product, which appears to be thymine propenal, was also observed. The dsDNA produces more furfural than furanone. The formation of these two products resulted from hydrogen ion or hydride transfer from C1' and C5' positions of the ribose to the oxo-chromium(V) center. Since no enhancements of these products (except propenal) were observed in the presence of oxygen, mechanisms pertaining to the participation of activated oxygen species may be ruled out. The oxidation of the G base is most likely associated with an oxygen atom transfer from the oxo-metallates to the double bond between C8 and N7 of the purine ring. The formation of the propenal may be associated with an oxygen-activated species, since a marginal enhancement of this product was observed in the presence of oxygen. The formation of furfural in higher abundance over 5-MF for dsDNA was attributed to the ease of hydrogen ion (or hydride transfer) from the C5' compared to C1' position of the ribose within a Cr(V)-DNA intermediate in which the metal center is bound to the phosphate diester moiety.

Alpha 1- and beta 2-adrenergic receptors co-expressed on cloned MDCK cells are distinct glycoproteins

We have explored the molecular differences between alpha 1- and beta 2-adrenergic receptors that are co-expressed by a clonally-derived cell line, Madin-Darby canine kidney clone D (MDCK-D). MDCK-D membranes were pre-labeled with selective alpha 1- and beta-adrenergic radioligands and were then solubilized with the non-ionic detergent digitonin. Solubilized alpha 1- and beta 2-adrenergic receptors were retained by immobilized wheat germ agglutinin and were eluted following addition of N-acetyl-D-glucosamine or sialic acid. Both receptors were also retained by immobilized Limax flavus lectin, a sialic acid-binding lectin. Lectins that were specific for N-acetyl-D-glucosamine residues did not bind to these receptors. These results indicate that both alpha 1 and beta 2 receptors are sialylated glycoproteins. The solubilized alpha 1- and beta 2-adrenergic receptors migrated with different elution profiles from an Ultragel AcA 34 column. The apparent molecular sizes of the digitonin-receptor complexes were 68A for the alpha 1 receptor and 55A for the beta 2 receptor. These results show that alpha 1- and beta 2-adrenergic receptors can be present on the same cell as distinct sialic acid-containing glycoproteins.

Solubilization of rat liver alpha 1-adrenergic receptors. Agonist specific alteration in receptor binding affinity

An improved method for the solubilization of the alpha 1-adrenergic receptors in rat liver, utilizing digitonin, glycerol and sonication, is described. The yield of solubilized receptors was approximately 20%. The soluble receptors showed characteristics similar to the membrane-bound alpha 1 receptors. However, upon solubilization, the affinity for the agonists (-)norepinephrine and (-)epinephrine increased 35- to 66-fold when compared to the affinity in the membranes. The affinity for antagonists remained unchanged. A number of synthetic partial agonists showed a less marked (5- to 10-fold) increase in affinity upon solubilization. These data are consistent with the notion that these receptors might be capable of existing in two distinct conformational states with the high affinity state for agonists being favored by solubilization.

Adrenoceptors: molecular nature and role in atopic diseases

Since Szentivanyi proposed the idea that asthma and other atopic diseases are due to a beta adrenergic defect there has been much interest in the role of the adrenergic receptors in allergy. The radioactive ligand binding techniques developed within the last few years have greatly increased our knowledge concerning the molecular nature of the adrenoceptors and the events following receptor stimulation. The adrenoceptors have shown to be very dynamic structures. Their number and affinity may be altered due to various physiological and pharmacological stimuli. Their role in the pathogenesis of atopic diseases has not been definitely settled, but there seem to be a true beta adrenergic hyporesponsiveness and alpha hyperresponsiveness in asthma. This article briefly describes the radioligand binding technique and summarizes our present knowledge of the nature of the alpha and beta adrenoceptors and their possible role in atopic diseases.

The hepatic adrenergic receptors

The presence of both alpha- and beta-adrenergic receptors in liver designated the hepatic plasma membrane as a useful tool for the elucidation of the mechanisms by which the hormonal signal is transferred through the membrane via a coupling system to an amplifying entity. This process is well documented for the beta-adrenergic receptor which is linked to adenylate cyclase, whereby it modulates the cyclic AMP level. Much less is known about the alpha-adrenergic receptor. Recently, two factors have contributed to a renewed interest in alpha- and beta-adrenergic receptors in liver: i) The fact that activation of glycogenolysis in isolated liver parenchymal cells by epinephrine may be mediated by either alpha- or beta-adrenergic receptors, depending on the species or on the state of nutrition, and not only by beta-adrenergic receptors as previously thought. ii) The existence of specific adrenergic agonists and antagonists radiolabeled to a high specific activity which has permitted the characterization of adrenergic receptors in terms of nature, number, affinity and regulation. The present review will be devoted to the recent progress made in the physiological, pharmacological and biochemical characterization of alpha- and beta-adrenergic receptors in the liver.

Alpha-Adrenergic receptors modulate beta-receptor affinity in rat kidney membranes

Adrenergic receptors were first classified into two calsses--alpha and beta--on the basis of the relative pharmacological potencies of agonist compounds, and this classification has been supported by subsequent studies. In some tissues, such as the heart and liver, they exert similar physiological responses, and in other tissues, such as the uterus and vasculature, they have opposing roles. The occurrence of both classes of receptor in the same tissue lewwds to the problem of what determines whether the overall response observed is alpha-type or beta-type, as adrenaline and noradrenaline bind to both receptor classes. Furthermore, direct binding studies have demonstrated that the two receptor classes are distinct and separate entities. We show here that stimulation of alpha-receptors in renal membranes causes a specific decrease in the affinity of the agonist compound isoprenaline for beta-receptors in the same membranes. This demonstrates that interactions occur between renal alpha- and beta-adrenergic receptors. Such interactions may modulate the response of the kidney to sympathetic stimulation.