A light and electron microscopic study of the quadriflagellate green algaSpermatozopsis exsultans

The green flagellateSpermatozopsis exsultans Korshikov has been studied in culture by light and electron microscopy. The organism is naked, bears four flagella and is conspicuously spirally twisted. The ultrastructure and location of cell organelles (except the flagellar apparatus) has been investigated in detail using an absolute configuration analysis. With the exception of a doubling of the flagella and of the secondary cytoskeletal microtubule system,S. exsultans has the exact same complement of organelles occupying the same relative positions as has been described forS. similis. The two species are therefore correctly placed in the same genus. The usefulness of absolute orientations of cell organelles for green algal taxonomy and phylogeny is stressed.Dedicated to Prof.M. Mix on the occasion of her 60th birthday.     

GC-MS identification of GA20-13-O-glucoside formed from GA20 in normal plants and dwarf-1 mutants ofZea mays L.

After feeding GA₂₀ to excised seedlings ofZea mays L. normals (N) and dwarf-1 mutants (d1), GA₂₀-13-O-glucoside (9) was identified by HPLC and by GC-MS of its permethylated derivative. The glucosylation rate of GA₂₀ was found to be higher in the dwarf-1 mutant (26%) than in the normal plant (3.6%). This article includes a GC-MS study in which diagnostic fragments from the spectra of permethylated synthetic GA glucosides have been selected that proved to be useful for the identification of permethylated GA glucosides.     

Internal motions in yeast phenylalanine transfer RNA from 13C NMR relaxation rates of modified base methyl groups: a model-free approach

Internal motions at specific locations through yeast phenylalanine tRNA were measured by using nucleic acid biosynthetically enriched in 13C at modified base methyl groups. Carbon NMR spectra of isotopically enriched tRNA(Phe) reveal 12 individual peaks for 13 of the 14 methyl groups known to be present. The two methyls of N2,N2-dimethylguanosine (m22G-26) have indistinguishable resonances, whereas the fourteenth methyl bound to ring carbon-11 of the hypermodified nucleoside 3' adjacent to the anticodon, wyosine (Y-37), does not come from the [methyl-13C]methionine substrate. Assignments to individual nucleosides within the tRNA were made on the basis of chemical shifts of the mononucleosides [Agris, P. F., Kovacs, S. A. H., Smith, C., Kopper, R. A., & Schmidt, P. G. (1983) Biochemistry 22, 1402-1408; Smith, C., Schmidt, P. G., Petsch, J., & Agris, P. F. (1985) Biochemistry 24, 1434-1440] and correlation of 13C resonances with proton NMR chemical shifts via two-dimensional heteronuclear proton-carbon correlation spectroscopy [Agris, P. F., Sierzputowska-Gracz, H., & Smith, C. (1986) Biochemistry 25, 5126-5131]. Values of 13C longitudinal relaxation (T1) and the nuclear Overhauser enhancements (NOE) were determined at 22.5, 75.5, and 118 MHz for tRNA(Phe) in a physiological buffer solution with 10 mM MgCl2, at 22 degrees C. These data were used to extract two physical parameters that define the system with regard to fast internal motion: the generalized order parameters (S2) and effective correlation times (tau e) for internal motion of the C-H internuclear vectors.(ABSTRACT TRUNCATED AT 250 WORDS)     

The genotypic response of mouse embryos to multiple freezing variables

Four- and eight-cell embryos from 3 mouse genotypes were cryopreserved to study the relationship of genetics and freezing variables on post-thaw survival. Embryos from outbred N:NIH(S), N:NIH(S)-B and inbred (C57BL/6N) mice were exposed to 1 of 2 cryoprotectants (glycerol [GLYC] versus dimethyl sulfoxide [DMSO]) and stored in 1 of 2 containers (ampules [AMP] versus straws [STR]). Containerized embryos were cooled at a rate of 0.5 degrees C/min to a minimum of -35 degrees C, transferred into liquid nitrogen, and later thawed and cultured in vitro. Genotypic differences (p less than 0.05) were noted for 4 interrelated embryo characteristics including post-thaw survival (PTS), embryo degeneration rate (EDR), and quality grade (QG) and viability grade (VG) ratings. The PTS for outbred embryos was greater (p less than 0.05) in GLYC than DMSO, whereas inbred C57BL/6N embryos survived similarly (p greater than 0.05) in either cryoprotectant. Compared to DMSO counterparts, embryos from GLYC-treated outbred groups had improved QG and VG ratings and reduced EDR (p less than 0.05), but comparable results were observed between GLYC- AND DMSO-treated embryos in the C57BL/6N group. Between genotypes, type of container affected PTS and EDR (p less than 0.05) but not QG or VG ratings (p greater than 0.05). Within genotypes, PTS generally ranged 15 to 20% higher (p less than 0.01) in AMP than STR groups. Increased PTS was noted in outbred mouse x GLYC x AMP groups; however, based on the degrees of difference, the inbred C57BL/6N strain appeared less affected by this 3-way interaction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Continuous production of L-phenylalanine by transamination

L-Phenylalanine was produced continuously from L-as-partate and phenylpyruvate by transaminase from a newly screened Pseudomonas putida strain. The process was carried out with an isolated enzyme in homogeneous phase in an enzyme membrane reactor and with immobilized whole cells in a stirred tank reactor, respectively. Due to the difference in transport resistance, the productivity of the free enzyme in homogeneous phase (72 mmol/L h) was about 3 times higher than the productivity achieved using immobilized cells. However, a better stability of the biocatalyst was observed with immobilized cells.     

The maize autonomous element Activator (Ac) shows a minimal germinal excision frequency of 0.2%–0.5% in transgenic Arabidopsis thaliana plants

Summary The autonomous mobile element Activator from Zea mays was introduced into Arabidopsis thaliana via Agrobacterium-mediated gene transfer. The use of a chimaeric construct, where the Ac element is located in the leader of the neomycin phosphotransferase (NPT II) gene, enabled the excision of Ac to be monitored by assaying for the reconstitution of NPT II gene activity. Using this approach, the transpositional activity of AC was initially studied in primary transformants. About 50% of the regenerating Ac transformants showed evidence for excision of the element. Reintegration of Ac was confirmed by Southern blot analysis. Transposition events are transmitted to the F1 generation with a minimal frequency of 0.3%. In a few exceptional cases they are detected in a high proportion of the F1 generation. Seedlings from the F2 and F3 generations were assayed for the rate of germinal excisions by scoring for kanamycin resistance. The minimal frequency of germinal excision events amounts to 0.2%–0.5% and hence allows the use of the Ac element for gene tagging purposes in A. thaliana.     

Studies of the oxysterol inhibition of tumor cell growth

The oxysterols 3 beta-hydroxy-5 alpha-cholest-8-en-11-one, 3 beta-hydroxy-5 alpha-cholest-8-en-7-one, 3 beta-hydroxy-5 alpha-cholest-8(14)-en-7-one, 3 beta-hydroxy-4,4'-dimethylcholest-5-ene-7 one, 4,4'-dimethylcholest-5-ene-3 beta, 7 alpha-diol, 4,4'-dimethylcholest-5-ene-3 beta, 7 beta-diol, lanost-8-ene-3 beta, 25-diol, 25-hydroxylanost-8-en-3-one, 9 alpha, 11 alpha-epoxy-5 alpha-cholest-7-en-3 beta-ol, 3 beta-hydroxycholest-5 alpha-en-22-one, and 3 beta-hydroxycholest-5-en-22-one oxime were evaluated with respect to their ability to inhibit cell growth. All of the sterols were found to possess cytotoxicity when incubated with hepatoma (HTC) and lymphoma (RDM-4) cells in culture at 10-30 microM concentrations.     

Bioluminescence of the insect pathogen Xenorhabdus luminescens

Luminescence of batch cultures of Xenorhabdus luminescens was maximal when cultures approached stationary phase; the onset of in vivo luminescence coincided with a burst of synthesis of bacterial luciferase, the enzyme responsible for luminescence. Expression of luciferase was aldehyde limited at all stages of growth, although more so during the preinduction phase. Luciferase was purified from cultures of X. luminescens Hm to a specific activity of 4.6 x 10(13) guanta/s per mg of protein and found to be similar to other bacterial luciferases. The Xenorhabdus luciferase consisted of two subunits with approximate molecular masses of 39 and 42 kilodaltons. A third protein with a molecular mass of 24 kilodaltons copurified with luciferase, and in its presence, either NADH or NADPH was effective in stimulating luminescence, indicating that this protein is an NAD(P)H oxidoreductase. Luciferases from two other luminous bacteria, Vibrio harveyii (B392) and Vibrio cholerae (L85), were partially purified, and their subunits were separated in 5 M urea and tested for complementation with the subunits prepared from X. luminescens Hb. Positive complementation was seen with luciferase subunits among all three species. The slow decay kinetics of the Xenorhabdus luciferase were attributed to the alpha subunit.     

Influence of ethanol on the activities of 3-hydroxy-3-methylglutaryl-coenzyme A-reductase and squalene-hopene-cyclase in Zymomonas mobilis

Summary The influence of different primary aliphatic alcohols on the activities of two key enzymes in hopanoid biosynthesis of Zymomonas mobilis was investigated. By use of ¹⁴C- and ³H-labelled substrates the enzymes 3-hydroxy-3-methylglutaryl-CoA-reductase and squalene-hopenecyclase were detected with activities of 1.6 pmol x (min x mg protein)^-1 and 2.3 pmol x- (min x mg protein)^-1, respectively. Cells grown in the presence of 6% (v/v) ethanol did not show higher activities of these enzymes than cells grown in the presence of 1% (v/v) ethanol. Furthermore, 3-hydroxy-3-methylglutaryl-CoA-reductase was not activated by ethanol. However, ethanol activated the squalene-hopene-cyclase when added to the enzyme test system. Besides ethanol, propanol also had a positive effect on the squalene-hopene-cyclase: the enzyme's activity increased 1.7-fold in the presence of either alcohol at a concentration of 6% (v/v). This corresponded with a similar increase of hopanoid content of whole cells when grown in the presence of 6% (v/v) added ethanol or propanol. These results indicated that the squalene-hopene-cyclase has a regulatory function in the alcohol dependent hopanoid biosynthesis of Z. mobilis.Abbreviation HMG-CoA-reductase 3-hydroxy-3-methylglutaryl-coenzyme A-reductase