Photoaffinity labeling with [3H]RU 28362: a powerful tool for the study of rat brain glucocorticoid receptors

In order to study the receptor system for adrenocortical steroids in rat brain the synthetic glucocorticoid RU 28362 (11 beta, 17 beta-dihydroxy-6-methyl-17 alpha-(1-propynyl) androsta-1,4,6-trien-3-one) has been used for photoaffinity labeling. Competition and dissociation studies revealed a single class of binding sites for RU 28362 in rat brain cytosol. Photoaffinity labeling was performed by u.v.-irradiation for 2 min with a coupling efficiency of about 25%. The high efficiency permitted investigation of crude cytosolic preparations under denaturating conditions. Sodium dodecyl sulfate (SDS) and high resolution two-dimensional gel electrophoresis confirmed the high specificity of the photoaffinity labeling. The molecular weight (93 kD) as well as the isoelectric point (5.6) evaluated by these methods corresponded well to data reported for the classical glucocorticoid receptor in rat liver.     

Extrinsic signals for monitoring the association reaction of proteins as introduced by fluorescent and non-fluorescent labels.

Two known dansyl labels (I, II) and 5-[2-(iodoacetamido)ethylamino]-1-naphthalene-sulfonic acid (III) and three new azo-dyes (IV - VI) were covalently attached to alpha-chymotrypsin and to basic pancreatic trypsin inhibitor by four different reactive groups. In order to protect the contact region of the proteins the complex of the two proteins was labeled. Advantage was taken of the fact that a group which is buried in the complex reacts about (see article) times slower than a group which is always exposed (K = dissociation equilibrium constant, [C] = concentration of the complex). The complex was dissociated at pH 3 and the labeled proteins were isolated by column chromatography. They were fully active. The dansyl label was immobilized when introduced by dansyl chloride but highly mobile when attached via the longer imidoester group (II). Changes of absorption and of fluorescence which occur when differently labeled reaction partners recombine were studied. Changes in absorption (up to 18%) were mainly due to interactions of the label of one protein with the other protein. Fluorescence changes of up to 480% could be obtained. They were interpreted in terms of a F?rster type energy transfer between donor and acceptor labels and changes of absorption and quantum yield due to interactions of the labels with the proteins. The kinetic constants of complex formation are not seriously altered by the labels (B?sterling, B & Engel, J. (1976) this J. 357, 1297-1307, succeeding). It is concluded that the labeling technique may be of general value for kinetic and equilibrium studies of protein associations.     

Mechanisms of protein kinase C regulation of airway contractility

To elucidate the role of protein kinase C (PK-C) in regulating airway contractility, the effects of PK-C activation with phorbol esters, 12-deoxyphorbol 13-isobutyrate (DPB), and phorbol 12-myristate 13-acetate (PMA), and with the diacylglycerol analogue 1-oleoyl-2-acetate-rac-glycerol (OAG) were separately evaluated in isolated rabbit tracheal smooth muscle (TSM) segments. The latter agents produced dual and opposing contractile effects, with DPB being the most potent. Lower doses of DPB (less than or equal to 10(-6) M) elicited significant increases in isometric tension in both untreated TSM, as well as in TSM half-maximally precontracted with methacholine. These potentiated TSM contractions were inhibited by the Ca2+ channel blockers, nifedipine (10(-4) M) and diltiazem (10(-5) M). In contrast, higher doses of DPB (greater than or equal to 10(-6) M) induced airway relaxation, which was ablated by preinhibition of the electrogenic Na+-K+ pump with ouabain (5 x 10(-6) M) or K+-free buffer. Indeed, in separate experiments DPB (10(-7) M) was found to significantly potentiate the functional activity of the Na+-K+ pump, an effect occurring independent of inhibition of Na+-H+ exchange with amiloride (10(-4) M) or extracellular Ca2+ influx with nifedipine (10(-4) M).(ABSTRACT TRUNCATED AT 250 WORDS)     

A large, efficient and inexpensive bacterial growth chamber

The construction of a 200 liter bacterial growth chamber for a total cost of less than $400 is described. The chamber was designed for growth of aerobic organisms and therefore provides high rates of aeration and mixing. The growth of Escherichia coli K₁₂ in the chamber was similar to growth in small flasks on a rotary shaker. Azotobacter vinelandii OP growth is slower in the growth chamber than in small, shaken flasks. Under the growth conditions described, kilogram quantities of bacterial cells are obtained from a single culture.     

Function of the delipidated beta-adrenergic receptor appears to require a fatty acid or a neutral lipid in addition to phospholipids

Detergent-solubilized preparations of the beta-adrenergic receptor (R) and of the guanyl nucleotide binding proteins (Gs) were extensively treated to remove phospholipids and cholesterol. Reconstitution of an R-Gs system was subsequently performed in the presence of a mixture of natural phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine or the synthetic dioleoyl derivatives of the same phospholipids. In both cases, an additional lipid was required for the agonist-dependent activation of Gs. The requirement could be fulfilled by alpha-tocopherol, or by unsaturated fatty acids such as oleic acid. Inclusion of this non-phosphorylated lipid in the reconstituted system enhanced the isoproterenol-dependent activation of Gs by guanosine 5'-O-[gamma-thio]triphosphate 16-33-fold. The rate of activation was largely dependent on the addition of the agonist. Efficient functional reconstitution of R-Gs was thus achieved in a totally defined lipid system. Additional studies of the reconstituted system and of the native membrane led to the notion that the non-phosphorylated lipid plays a role in the function of the hormone-R complex.