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.     

Heartbeat and Economic Decisions: Observing Mental Stress among Proposers and Responders in the Ultimatum Bargaining Game

The ultimatum bargaining game (UBG), a widely used method in experimental economics, clearly demonstrates that motives other than pure monetary reward play a role in human economic decision making. In this study, we explore the behaviour and physiological reactions of both responders and proposers in an ultimatum bargaining game using heart rate variability (HRV), a small and nonintrusive technology that allows observation of both sides of an interaction in a normal experimental economics laboratory environment. We find that low offers by a proposer cause signs of mental stress in both the proposer and the responder; that is, both exhibit high ratios of low to high frequency activity in the HRV spectrum.     

Glucosinolate contents in maca (Lepidium peruvianum Chacón) seeds, sprouts, mature plants and several derived commercial products

Several products derived from processed maca hypocotyls (Lepidium peruvianum Chacón, previously known asL. meyenii Walp.) were surveyed for glucosinolate content and quantified by HPLC analysis. These included pills, capsules, flour, liquor, tonic and mayonnaise. Different plant organs such as fresh hypocotyls and leaves, seeds, dry hypocotyls, and sprouts were also included in the survey. The most abundant glucosinolates detected in fresh and dry hypocotyls and leaves were the aromatic glucosinolates, benzylglucosinolate (glucotropaeolin) and p-methoxybenzylglucosinolate. Maca seeds and sprouts differed in profile from hypocotyls and leaves due to the modification of benzylglucosinolate. No glucosinolates were detected in liquor and tonic, while mayonnaise had only trace amounts of those glucosinolates. It had instead allylglucosinolate (sinigrin), which is an aliphatic glucosinolate. The pills, capsules and flour had the same glucosinolates as those observed in hypocotyls, but in variable amounts. The richest sources of glucosinolates were seeds, fresh hypocotyls and sprouts, in that order.     

Indole-3-ethanol oxidase in Phycomyces blakesleeanus. Is indole-3-ethanol a “storage pool” for IAA?

Indole-3-ethanol (IEt) was extracted from Phycomyces blakesleeanus Bgff. and purified by TLC and HPLC. Identification was performed by mass spectrum. The HPLC-purified compound showed an UV-spectrum typical for indoles, with absorption maxima at 220 and 281 nm. The IEt content varied between 1.5 nmol (g fresh weight)⁻¹ and 5.6 nmol (g fresh weight)⁻¹. The observed variations were strongly correlated with certain developmental stages of the fungus. Furthermore, the decrease of IEt between 60 and 84 h of fungal development coincides with a high IEt oxidase activity. The product of the enzyme reaction was indole-3-acetaldehyde, which was identified by co-chromatography with an authentic standard in several TLC and HPLC systems and by chemical conversion to indole-3-acetaldoxime.     

Nucleotide sequence of the colicin B activity gene cba: consensus pentapeptide among TonB-dependent colicins and receptors.

Colicin B formed by Escherichia coli kills sensitive bacteria by dissipating the membrane potential through channel formation. The nucleotide sequence of the structural gene (cba) which encodes colicin B and of the upstream region was determined. A polypeptide consisting of 511 amino acids was deduced from the open reading frame. The active colicin had a molecular weight of 54,742. The carboxy-terminal amino acid sequence showed striking homology to the corresponding channel-forming region of colicin A. Of 216 amino acids, 57% were identical and an additional 19% were homologous. In this part 66% of the nucleotides were identical in the colicin A and B genes. This region contained a sequence of 48 hydrophobic amino acids. Sequence homology to the other channel-forming colicins, E1 and I, was less pronounced. A homologous pentapeptide was detected in colicins B, M, and I whose uptake required TonB protein function. The same consensus sequence was found in all outer membrane proteins involved in the TonB-dependent uptake of iron siderophores and of vitamin B12. Upstream of cba a sequence comprising 294 nucleotides was identical to the sequence upstream of the structural gene of colicin E1, with the exception of 43 single-nucleotide replacements, additions, or deletions. Apparently, the region upstream of colicins B and E1 and the channel-forming sequences of colicins A and B have a common origin.     

Catalytic and allosteric mechanism of AMP nucleosidase from primary, beta-secondary, and multiple heavy atom kinetic isotope effects

Adenosine 5'-phosphate was synthesized with specific heavy atom substitutions to permit measurement of V/K kinetic isotope effects for the N-glycohydrolase activity of the allosteric AMP nucleosidase and the acid-catalyzed solvolysis of these compounds. The effects of allosteric activation on the kinetic isotope effects together with the kinetic mechanism of AMP nucleosidase [DeWolf, W. E., Jr., Emig, F. A., & Schramm, V. L. (1986) Biochemistry 25, 4132-4140] indicate that the kinetic isotope effects are fully expressed. Comparison of individual primary and secondary kinetic isotope effects with combined isotope effects and the isotope effect of the reverse reaction indicated that kinetic isotope effects in AMP nucleosidase arise from a single step in the reaction mechanism. Under these conditions, kinetic isotope effects can be used to interpret transition-state structure for AMP nucleosidase. Changes in kinetic isotope effects occurred as a function of allosteric activator, demonstrating that allosteric activation alters transition-state structure for AMP nucleosidase. Kinetic isotope effects, expressed as [V/K(normal isotope]/[V/K(heavy isotope)], were observed with [2'-2H]AMP (1.061 +/- 0.002), [9-15N]AMP (1.030 +/- 0.003), [1'-2H]AMP (1.045 +/- 0.002), and [1'-14C]AMP (1.035 +/- 0.002) when hydrolyzed by AMP nucleosidase in the absence of MgATP. Addition of MgATP altered the [2'-2H]AMP effect (1.043 +/- 0.002) and the [1'-2H]AMP effect (1.030 +/- 0.003) and caused a smaller decrease of the 14C and 15N effects. Multiple heavy atom substitutions into AMP caused an increase in observed isotope effects to 1.084 +/- 0.004 for [1'-2H,1'-14C]AMP and to 1.058 +/- 0.002 for [9-15N,1'-14C]AMP with the enzyme in the absence of ATP.(ABSTRACT TRUNCATED AT 250 WORDS)