Ultraviolet flash photolysis of gramicidin-doped lipid bilayers

We have examined the rate of gramicidin channel conductance inactivation by ultraviolet photolysis using 0.1 millisecond light flashes. The lower limit on the channel photolysis reaction rate has been reduced by four orders of magnitude over previous observations. Monoolein/hexadecane bilayers formed in 1.0 M KCl were doped with (1-3) x 10(6) gramicidin A' channels and exposed to a broad-spectrum light flash. The flash reduced membrane conductance abruptly by approx. 16%. Following the flash, a further slow reduction of approx. 3% was observed followed by a slow recovery of approx. 4%. The post-flash decay and recovery may be due to slow chemical reactions, conformational relaxations, or changes in the equilibrium between aqueous, lipid-bound, and channel-forming dimerized gramicidin. Under our experimental conditions, gramicidin M was insensitive to light flashes compared to gramicidin A', demonstrating that for gramicidin A' the photolysis mechanism depends specifically on the tryptophan side-chain. Flash photolysis of a membrane containing a small population of channels (approx. 30) indicated that the decay is due to the sudden inactivation of several channels. The recovery appears to result from insertion of normal channels into the membrane. Flash photolysis of single-channel membranes showed that the flash causes abrupt, complete channel inactivation.     

Proton NMR study of the myoglobin reconstituted with meso-tetra(n-propyl)hemin

Spectrophotometric titration of meso-tetra(n-propyl)hemin with sperm-whale apomyoglobin revealed their 1:1 complex formation. The purified reconstituted metmyoglobin bound with an equal molar amount of CN- and the second CN- ligation was not evidenced, suggesting that the hemin is not loosely attached to the globin surface, but incorporated into the heme pocket. The hyperfine-shifted proton NMR spectrum of the deoxy myoglobin revealed the proximal imidazole NH resonance at 85.1 ppm to indicate the formation of the Fe-N(His-F8) bond. The eight pyrrole protons of the hemin of myoglobin in the absence of external ligand were observed as a single peak at -16 ppm. This indicates the electronic symmetry of the hemin and the low-spin configuration of the heme iron. The pyrrole-proton NMR patterns of the cyanide and deoxy myoglobins were found to be remarkably temperature-dependent, which was consistently explained in terms of the free rotation of the prosthetic group. The NMR results suggest that introduction of meso-tetra(n-propyl)hemin totally disrupts the highly stereospecific heme-globin contacts, making the prosthetic group mobile in the heme cavity.     

X-ray induced rearrangements between germ-line limited and soma chromosomes of Acricotopus lucidus (Diptera,Chironomidae)

The germ-line limited chromosomes (Ks) [K being derived from Keimbahn (Bauer, 1970)] of Acricotopus lucidus were studied in gonial and differential mitosis. After C-banding the soma chromosomes (Ss) are stained only at their centromeric regions whereas the Ks exhibit centromeric, intercalary and terminal heterochromatin. By X-raying sperms it was attempted to transfer K sections on or into Ss in order to bring finally S-linked K sections to polytenization in the salivary glands, and to obtain more knowledge about the structure of Ks. Seven F₁-larvae were detected with K-S-rearrangements: four with insertions of heterochromatic segments, two with insertions of sections with S-homologous banding pattern and one with a translocated K chromosome part, which consists of S-homologous euchromatic sections as well as of an intercalary and a terminal heterochromatic segment. The present results strongly suggest that the Ks of A. lucidus are derived from the Ss by rearrangements and by formation and accumulation of repetitive sequences.     

Genetical and biochemical comparisons of alcohol dehydrogenase isozymes from Anastrepha fraterculus and A. obliqua (Diptera: Tephritidae): Evidence for gene duplication

The electrophoretic patterns of the enzyme alcohol dehydrogenase (ADH) from Anastrepha fraterculus and A. obliqua were studied. Two loci were found to code for the enzyme in A. fraterculus, and three in A. obliqua. In both species, all isozymes were active in third-instar larvae. A cationic isozyme (Adh-1) was active mainly in the visceral fat body of both species. In A. fraterculus, the locus had an anionic polymorphic isozyme (Adh-3) that was detected in the parietal fat body. In addition to these two loci, a third locus for an anionic isozyme (Adh-2), which was active in the digestive tube of larvae, was present in A. obliqua and probably resulted from gene duplication. For both species, multiple forms of the isozymes are formed by binding of an NAD-carbonyl compound, as in Drosophila melanogaster. Both larvae and early pupae of A. obliqua had almost twice the specific ADH activity as A. fraterculus. The ethanol content of the host fruit infested with A. obliqua (red mombim) was also higher than that of the host fruit infested with A. fraterculus (guava).This research was supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnologico (CNPq-PIG 40.2486/82).     

Three distinct H-2Ks molecules differing at the carboxy terminus are expressed on a tumor from SJL/J mice

A dimethylbenzanthracene-induced leukemia of H-2s origin expressed at least two class I molecules on the cell surface that were precipitated by anti-H-2.19, an alloantiserum prepared against the private H-2Ks specificity. Mapping studies in recombinant inbred strains along with comparisons of tryptic peptide maps and N-terminal sequences indicated that the proteins were virtually identical and probably encoded by the same class I gene. When cells were labeled in the presence of tunicamycin, the proteins precipitated by anti-H-2.19 were further resolved into three distinct peptides. Experiments were performed to determine which of these various proteins were phosphorylated and which were recognized by an anti-synthetic peptide serum directed against the ultimate C-terminus of H-2K class I molecules. The results indicate that a single class I gene from the H-2Ks region may encode three class I molecules that differ only at the C-terminus due to alternative splicing of pre-mRNA.     

Plant contents and quality of makhana (Euryale ferox)

Summary As a part of integrated study of makhana, the mineral contents of the plant parts and the fruits of makhana (Euryale ferox) have been presented here. It has been observed that the fruits were not only rich in minerals but also in protein. The plant parts also contained high amounts of micronutrients. Its fruits are, therefore, a good supplement for minerals which are produced from otherwise agriculturally waste (water-logged) areas.     

Characterization of a parasporal inclusion body from sporulating, enterotoxin-positive Clostridium perfringens type A.

Inclusion bodies (IB) synthesized during sporulation and enterotoxin formation by Clostridium perfringens NCTC 8239 and 8798 were isolated and characterized. IB were isolated by disruption of sporangia by sonication in the presence of tetrasodium EDTA and phenylmethylsulfonyl fluoride. Fractionation was carried out in a linear gradient of sodium bromide, sucrose, or diatrizoate sodium. Denaturing and reducing agents were necessary to solubilize the IB. An alkylating agent was required to prevent reaggregation of the subunits. Molecular weight, compositional, and serological analyses and peptide mapping revealed strong similarities between the IB subunits and the enterotoxin synthesized during sporulation by C. perfringens. IB appear to represent the structural component where overproduced enterotoxin accumulates intracellularly. Enterotoxin-like subunits in the IB appeared to be held together by noncovalent and disulfide bonds, which were generally resistant to the action of intracellular proteases of C. perfringens, trypsin, or trypsin plus bile salts.     

Biosynthesis of methylphosphomannosyl residues in the oligosaccharides of Dictyostelium discoideum glycoproteins. Evidence that the methyl group is derived from methionine

The phosphorylated oligosaccharides of Dictyostelium discoideum contain methylphosphomannosyl residues which are stable to mild-acid and base hydrolysis (Gabel, C. A., Costello, C. E., Reinhold, V. N., Kurtz, L., and Kornfeld, S. (1984) J. Biol. Chem. 259, 13762-13769). Here we present evidence that these methyl groups are derived from [methyl-3H]methionine, in vivo and [methyl-3H]S-adenosylmethionine in vitro. About 18% of the macromolecules secreted from vegetative cells labeled with [methyl-3H]methionine are released by digestion with preparations of endoglycosidase/peptide N-glycosidase F. The majority of the released molecules are sulfated, anionic high mannose-type oligosaccharides. Strong acid hydrolysis of the [3H]methyl-labeled molecules yields [3H]methanol with kinetics of release similar to those found for the generation of Man-6-P from chemically synthesized methylphosphomannose methylglycoside. Treatment of the [3H]methyl-labeled molecules with a phosphodiesterase from Aspergillus niger which is known to cleave this phosphodiester also releases [3H]methanol from a portion of the oligosaccharides. In vitro incorporation of [methyl-3H]S-adenosylmethionine into endogenous acceptors found in membrane preparations shows that the [3H]methyl group of the methylphosphomannose residues can be derived from this molecule.     

A two-sample test sensitive to crossing hazards in uncensored and singly censored data

Savage score statistics are employed to develop a test for comparing survival distributions with right-hand singly censored data. The procedure is motivated by the interest in developing a powerful method for determining differences when true survival distributions cross. Examination of small-sample characteristics under the null hypothesis indicate that asymptotic critical values yield a slightly conservative test. Power of the test compares favorably with other criteria, including the modified Smirnov procedure, particularly if there is a single crossing of the survival curves.     

Status of the DNA-RNA-protein synthesizing system in neurons of the sensomotor cortex of the brain of the 30-day-old rat

By means of the electron cytochemical method ribonucleoprotein (RNP) particles, condensed chromatin (CCh) and ribosomes of cytoplasm are describe in normo- and hyperchromic neurons (HChN) of the V and VI layers of the sensomotor cortex. The normochromic neurons are characterized by nearly a complete absence of CCh, a great number of fibrillar RNP particles. The ribosomes of cytoplasma are organized as polysomes. This demonstrates a high metabolic activity of the DNA-RNA-protein system in these cells. In nuclei of one HChN group numerous small CCh clumps are revealed, amount of RNP particles does not change noticeably, comparing the nuclei of the normochromic cells. In cytoplasm a partial dissociation of polysomes takes place. All this demonstrates a decreased RNA synthesis in the nucleus and protein in cytoplasm of the given cells. In another HChN group the nucleus is filled with large CCh clumps. The number of fibrillar RNP particles decreases noticeably, and the number of granular ones increases. A complete dissociation of polysomes occurs. This demonstrates that in the cells mentioned not only RNA and protein synthesis is decreased, but the processing and nucleo-cytoplasmic transport of RNA is disturbed. The presence of transitional forms between the neuronal forms described makes it possible to suppose certain cyclicity in the work of their plastic apparatus, the normo- and hyperchromic neurons being morphologic equivalents of certain phases of the cycle.