“Slim” Nucleosides and Nucleotides. I. Synthetic,Structural and Biophysical Investigations of Showdomycins

Abstract

A new, convenient, and short synthesis of 2′-deoxyshowdomycin, along with an improved procedure for the preparation of showdomycin, have been presented. A single-crystal X-ray structure of l-benzyl-2′-deoxyshowdomycin (9) has been reported. Conformational studies using C.D. indicated that showdomycin exists predominantly in an anti conformation in aqueous solution. Molecular mechanics calculations using AMBER point to comparable binding energy of showdomycin-adenosine pair with the natural uridine-adenosine pair, but with a significant base-ribose conformational deviation from the natural array in the former. Implications of such a conformational deviation on tumor and viral replications have been discussed. Base-pairing studies employing high resolution NMR spectroscopy indicate that both showdomycin and epishowdomycin base-pair with adenosine-5′-monophosphate (AMP); however, while showdomycin also shows evidence of stacking, that was absent in epishowdomycin. Molecular modeling studies using QUANTA/CHARMm show that showdomycin is capable of forming a homopolymer duplex by base-pairing with poly(A), but with a considerably broader and deeper major groove. A heteropolymer duplex with a single insert of showdomycin exhibits tighter coiling at the point of insertion. A ten-picosecond dynamics simulation of the above heteroduplex revealed relaxation of the helix with disruption of H- bonding for two base pairs on either side of the insertion point forming a large central cavity.     

Megaspore development in Selaginella. I. “Wicks”, their presence,ultrastructure, and presumed function

Summary Structures have been found in the locular space between the tapetal cells and megaspores in Selaginella argentea and S. kraussiana that enter the megaspore wall and extend to the plasma membrane of the megaspore cytoplasm. We have called these structures wicks. Unless special fixation procedures are used wicks are either very poorly preserved or not apparent. Wicks appear to be routes for the transport of materials from the tapetum to developing megaspores. The entry of the wicks into the megaspore wall and their passage throughout the wall implies that the megaspore wall of Selaginella is a three-dimensional mesh-work of inter-connecting spaces. Wicks have several macromolecular-sized subunits, and the results of our histochemical reactions indicated the presence of glycoprotein and/or mucopolysaccharide. X-ray microanalysis of the S. convoluta exospore showed that silicon is present in rod-shaped structures between units of the exospore in mature megaspores. Because of the size and form of the structures between the exospore units we consider that they are remnants of wicks stabilized by silicon.Present address:Cátedra de Palinologia, Museo de La Plata, Paseo del Bosque s/nro., 1900 La Plata, Argentina.     

The ultrastructure of holdfasts, “rhizoids”, and “slime tracks” in thraustochytriaceous fungi and Labyrinthula spp.

Summary The fine structure of the holdfasts or rhizoids is described for the thraustochytriaceous organisms, Thraustochytrium motivum, Schizochytrium aggregatum, and an unidentified organism, denoted T-20, which resembles S. aggregatum and Labyrinthula spp. Labyrinthula algeriensis and L. minuta slime track ultrastructure is also described. The holdfasts, rhizoids, and tracks have the same basic fine structure and are collectively termed ectoplasmic nets. They are delimited by a unit membrane which is in continuity with the plasmalemma, contain no cytoplasmic organelles only membrane-limited cisternae, and contain a fibrogranular ground substance. The nets appear to arise from one or as many as 20 organelle complexes consist of an approximately disk-shaped electron-dense granular aggregate in which are embedded portions of cisternae of the endoplasmic reticulum or perinuclear clear continuum. The cisternae appear to contribute small (ca. 17 nm diameter) vesicles to the granular aggregate which coalesce to form internal membranes of the net elements. The sagenogenetosome underlies the plasmalemma where it evaginates to form the delimiting membrane of the main trunk element of the net. No continuous membrane separates the net contents from the cytoplasm, only the granular aggregate.In L. algeriensis, L. minuta, and T-20 the net is necessary for motility of nonflagellated, nonamoeboid cells. Presence of the nets is not associated with motility in S. aggregatum and T. motivum. The possible taxonomic significance of the observations is discussed.Contribution No. 456, Virginia Institute of Marine Science, Gloucester Point, Virginia 23062.Supported in part by the Oceanography Section, National Science Foundation, NSF Grant GA-31014.     

A Review of: “Biological Recognition and Assembly,D. S. Eisenberg,J. A. Lake and C. F. Fox,Eds. Alan R. Liss,New York, 1980; hardbound, 355 pages, $52.00”

Two MMP-7-ase isoenzymes were purified 100-fold from rat muscle extract to apparent homogeneity, with an overall yield of 10%, using homogenization, ultracentrifugation, high-performance aqueous size-exclusion and high-performance anion exchange chromatography methods. When using a TSK G-2000SW column, the separation resulted in a 6-fold purification and 30% recovery of isoenzymes B and C. This concentrated enzyme extract was then passed through a TSK-DEAE-2SW column, using salt gradient at pH 7.5, with an additional 25-fold purification and 90% recovery of the isoenzymes. Two symmetrical enzyme peaks, representing isoenzymes B and C, were detected when performing purity tests of the active enzymes on the anion exchanger and reversed-phase HFLC columns. The procedures involved are extraction, ultracentri-fugation, chromatographies and enzyme assays and require less than five hours.