Transport Of Methyl Research Articles

A New Generation of "Cholaphanes": Steroid-Derived Macrocyclic Hosts with Enhanced Solubility and Controlled Flexibility.

The macrocyclic "cholaphanes" 3a-c were synthesized from the inexpensive steroid cholic acid. Like earlier relatives they feature substantial cavities with inward-directed hydroxyl groups, suitable for binding polar molecules such as carbohydrates in nonpolar media. New features are the externally directed alkyl chains, promoting solubility in organic solvents, and (in the case of 3b/c) reduced conformational freedom resulting from truncation of the steroidal side-chain. In particular, modeling shows that the smallest macrocycle 3c possesses very little flexibility, preferring an open conformation which is also revealed in the X-ray crystal structure of its pentahydrate. NMR studies indicated that all three cholaphanes form 1:1 complexes with octyl beta-D-glucoside in CDCl(3), with K(a) = 600-1560 M(-)(1). Cholaphanes 3b/c proved able to extract methyl beta-D-glucoside from aqueous solutions into CHCl(3). The transport of methyl beta-D-glucoside across a chloroform barrier was also demonstrated for 3c.

Characteristics of the melibiose transporter and its primary structure in Enterobacter aerogenes

Cells of Enterobacter aerogenes can grow on melibiose as a sole source of carbon. This suggests the presence of melibiose operon in this organism. We found that E. aerogenes cells possess both α-galactosidase activity and melibiose transport activity, which were induced by melibiose. Neither Na + nor Li + stimulated the melibiose transport. However, transport of methyl- β-thiogalactoside (TMG) was stimulated by Li + but not by Na +. These findings suggest that the major coupling cation for the melibiose transporter in E. aerogenes is H +. In fact, we observed H + entry into cells caused by an influx of melibiose and some of its analogs. We cloned the melB gene which encodes the melibiose transporter, and sequenced it. Deduced amino acid sequence of the transporter revealed that the melibiose transporter consists of 471 amino acid residues and the molecular weight was calculated to be 52 214 Da. The sequence showed high homology with the sequences of the melibiose transporters of Escherichia coli, Salmonella typhimurium and Klebsiella pneumoniae. Higher homology was found with the melibiose transporter of K. pneumoniae than with that of E. coli and S. typhimurium.

The role of ATP in the control of H+-galactoside symport in the yeast Kluyveromyces marxianus

Transport of methyl beta-D-thiogalactoside and p-nitrophenyl beta-D-galactoside is shown to proceed through the H+-lactose symporter of Kluyveromyces marxianus. Uptake of these compounds is strongly reduced under anaerobic conditions or aerobically in the presence of antimycin. It is shown that antimycin treatment affects p-nitrophenyl beta-D-galactoside uptake in a similar way as it affects the cellular amount of ATP, suggesting regulation of p-nitrophenyl beta-D-galactoside transport by ATP. Also, manipulation of cellular ATP by antimycin treatment followed by glucose incubation, or by aerobic incubation of cells with 2-deoxy-D-glucose, showed a similar dependence of galactoside uptake on the ATP level. Transport of the lipophilic cation tetraphenylphosphonium is affected by ATP variations in a similar way as galactoside influx. It is concluded that ATP regulates H+-galactoside symport by its influence on charge translocation. It is discussed that a membrane ATPase probably plays a central role in the control of the activity of H+-sugar symport.

Synthesis and Chiral Recognition of Optically Active Crown Ethers Incorporating a 9,9′-Biphenanthryl Moiety as the Chiral Center

Abstract Two chiral crown ethers incorporating a 9,9′-biphenanthryl moiety as the chiral center have been prepared, and their chiral recognition properties in transport of methyl (±)-phenylglycinate hydrochloride, (±)-1-phenylethylamine hydrochloride, and (±)-1,2-diphenylethylamine hydrochloride were examined.

ChemInform Abstract: SYNTHESIS OF CHIRAL CROWN ETHERS DERIVED FROM TRANS,TRANS‐ AND CIS,TRANS‐2,2′‐SPIROBIINDAN‐1,1′‐DIOLS. THEIR CHIRAL RECOGNITION AND COMPLEXATION PROPERTIES

AbstractDurch Umsetzung der chiralen Spirobiindan‐Derivate (I) mit den entsprechenden (V) werden die Kronenether (VI) und der offenkettige Polyether (VII) dargestellt [Bestimmung der absoluten Rotation von (Ia) durch Synthese des optisch reinen Diols über den Ester (III) (Ausb‐Angabe in g) und Oxidation zum Diketon (II), dessen optische Drehung aus der Literatur bekannt ist].

Synthesis of Chiral Crown Ethers Derived from trans, trans- and cis, trans-2,2′-Spirobiindan-1,1′-diols. Their Chiral Recognition and Complexation Properties

Abstract trans,trans-2,2′-Spirobiindan-1,1′-diol (1) was resolved as its (−)-ω-camphanic ester and the absolute rotation of the glycol 1 was determined. Two crown ethers and the acyclic analog were derived from (+)-1. Two crown ethers incorporating (+)-cis,trans-2,2′-spirobiindan-1,1′-diol were also prepared. Their chiral recognition properties in transport of methyl (±)-phenylglycinate hydrochloride and abilities to extract alkali metal picrates were investigated.

Kinetics and Thermodynamics of Interfacial Transfer

□ The kinetic barrier against the transport of methyl and ethyl nicotinates across the water-isopropyl myristate interface has been studied as a function of temperature using a rotating diffusion cell. The temperature dependence of the interfacial transfer kinetics has enabled calculation of the thermodynamic parameters for the process. It is evident from the results that, for the transferring solutes considered, the activation energy barrier is enthalpic, because there is a large positive entropy for transfer into the interfacial region.

Kinetic analysis of [formula omitted]-thiogalactoside symport in Saccharomyces fragilis

A theoretical description of initial uptake kinetics of H +/sugar symport is given, with emphasis on the differences between carrier and non-carrier systems. Transport of methyl β- d-thiogalactoside in Saccharomyces fragilis is shown to proceed via the inducible lactose transporter. Uptake of this sugar stimulates electrogenic H + influx. Together with the correlation between methyl β- d-thiogalactoside accumulation and the proton-motive force this shows that transport proceeds via H + symport. Kinetic analysis of initial influx revealed that transport proceeds via a single transport system, sensitive to changes in membrane potential. The pH dependence of the kinetic parameters showed that K app is almost pH insensitive, whereas V app decreases strongly at increasing extracellular pH. It is shown that transport proceeds, most likely, via a non-carrier system, with random binding of H + and sugar, in a system where binding of the first ligand does not influence binding of the second.