Interaction between calcium and ligand-binding sites of the purified acetylcholine receptor studied by use of a fluorescent lanthanide

The acetylcholine receptor isolated from $\text{Torpedo ocellata}$ binds about 10 moles of a fluorescent lanthanide, terbium, per mole α-bungarotoxin-binding site, a process which is accompanied by a fluorescence enhancement (λexcitation 295 nm, λemission 546 nm) which allows detection of receptor-Tb³⁺ complexes at μM concentrations. In presence of calcium two types of terbium-binding site are revealed, both with terbium dissociation constants of 18 ± 0.5 μM. About 60% of the sites bind calcium with an apparent dissociation constant of 1.1 ± 0.1 mM. Sites which interact with calcium also interact with activators of neural transmission, carbamylcholine and decamethonium, but not with the inhibitors, d-tubocurarine and α-bungarotoxin. Whether the displacement of calcium by chemical mediators is directly responsible for activator-induced changes in ion permeability of neural membranes is an important question raised by our experiments. The results show that fluorescent lanthanides can be an important tool in such studies.     

Localization of the central and peripheral SH-groups on the same polypeptide chain of yeast fatty acid synthetase

Purified fatty acid synthetase isolated from wild type yeast cells as well as from two different $\text{fas}$-mutant strains was reacted with (1-¹⁴C-)iodoacetamide. Tryptic digests of the ¹⁴C-carboxamidomethylated enzymes were fractionated on Sephadex G-50. Hereby, essentially only one radioactively labeled peptide was eluted from the column. From this it is concluded that under the experimental conditions employed only the “peripheral” SH-group of yeast fatty acid synthetase becomes alkylated. By sodium dodecylsulfate-polyacrylamide gel electrophoresis of the ¹⁴C-carboxamidomethylated fatty acid synthetase it was shown that in all three enzyme preparations studied the inhibitor is bound to the larger one of the two fatty acid synthetase subunits. These findings indicate that the larger fatty acid synthetase subunit accomodates not only the “central” but also the “peripheral” SH-group of the multienzyme complex.     

Book reviews

Ohne Zusammenfassung

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Book reviews

     

A common receptor protein for phage T5 and colicin M in the outer membrane of Escherichia coli B

The receptor protein for phage T5 was isolated from the outer membrane of Escherichia coli B and found to be also a receptor for colicin M. The receptor protein from a phage-resistant mutant inactivates neither the phage nor the colicin. Binding of colicin M to the receptor prevents binding of phage T5. It is concluded that phage T5 and colicin M bind to the same active area of this receptor protein. The receptor protein seems to consist of one polypeptide chain with a molecular weight of 85000.     

Die regulation der DNS-Synthese in Farngametophyten durch Licht

Zusammenfassung Bei Farnvorkeimen (Dryopteris filix-mas) steigert Blaulicht spezifisch DNS-Replikation und mitotische Aktivität, so daß sich die im Hellrot bzw. Blaulicht herangewachsenen Vorkeime, die gleichviel Trockensubstanz besitzen, bezüglich ihres DNS-Gehalts und ihrer Zellzahl wesentlich unterscheiden — Die Zelle scheint als Bezugssystem für RNS, Protein und entsprechende biochemische Größen ungeeignet zu sein. Der Gesamtkeimling ist das angemessene Bezugssystem.

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The regulation of DNA synthesis in fern gametophytes by light

Summary In young gametophytes (= sporelings) of the common male fern (Dryopteris filix-mas) short wavelength light (= blue light) specifically increases DNA replication and mitotic activity even if the sporelings have the same growth rate under blue and red light, as determined by dry matter increase. Cell number and DNA content of sporelings of the same age and the same dry matter content are much higher under blue than under red light (Figs. 1, 2). In the second part of the paper it is pointed out that the cell (or unit of DNA) may not be used as a system of reference for biochemical data such as protein or RNA content in the case of the fern sporelings (and possibly not in many other organisms either). The appropriate system of reference seems to be the entire multicellular system if precaution is taken that the systems grow with the same growth rate under the different experimental conditions (e.g. under blue and red light in the case of the fern sporelings).

     

Potential Role of Elicitins in the Interaction between Phytophthora Species and Tobacco

The potential role of extracellular elicitor proteins (elicitins) from Phytophthora species as avirulence factors in the interaction between Phytophthora and tobacco was examined. A survey of 85 Phytophthora isolates representing 14 species indicated that production of elicitin is almost ubiquitous except for isolates of Phytophthora parasitica from tobacco. The production of elicitins by isolates of P. parasitica correlated without exception with low or no virulence on tobacco. Genetic analysis was conducted by using a cross between two isolates of P. parasitica, segregating for production of elicitin and virulence on tobacco. Virulence assays of the progeny on tobacco confirmed the correlation between production of elicitin and low virulence.     

From the editors

[T]here had been theories that homosexuality might have a genetic basis. In June this year, these theories received a somewhat firmer basis. Researchers at the United States National Cancer Institute reported new evidence which suggests that some gay men may have a genetic predisposition to homosexuality. The research team led by molecular biologist Dean Hamer tested 40 pairs of homosexual brothers and found that 33 of the pairs shared genetic markers on a particular area of the X chromosome (called Xq28), indicating a link between homosexuality and a gene in that area. If followed-up research were to confirm the findings, then, it has been claimed, this would be the first example of a behavioral trait that has been found to have a genetic basis. The study does, however, leave some central questions unanswered. Some revolve around the link between genetics and the nature of sexuality itself. The others concern the ethical and social implications of the research....