The electrostatic potential and steric accessibility of reactive sites within Z-DNA.

A theoretical study of indices potentially useful for investigation of the reactivity of the recently discovered Z-DNA double helix is presented. The electrostatic potential minima and the steric accessibility of reactive sites are calculated. The effect of screening the phosphate groups by metal cations is investigated. The results are compared with those for the B-DNA double helix.     

The electrostatic molecular potential of yeast tRNAPhe. (I). The potential due to the phosphate backbone.

We present a preliminary theoretical study of the electrostatic potential surrounding yeast tRNAPhe by computing the component of this potential due to all the 76 phosphate groups of the molecule. The general features of the results obtained are discussed and deductions concerning the binding of Mg2+ ions to the molecule in relation to the potential are presented.     

Electron spin resonance studies on tooth phosphoproteins using manganese ions as probes.

The binding of manganese ion to tooth phosphoproteins and to model compounds containing carboxyl and phosphate groups was analyzed with the Langmuir equation applied to data obtained from esr spectra. The Langmuir isotherms suggested that both bovine molar and rat incisor phosphoprotein preparations bound manganese primarily to phosphate groups. A purified sample of the bovine dentin protein showed a greatly increased number of binding sites for manganese as well as an increased affinity.     

The effect of spermine binding on the reactivity of DNA towards carcinogenic alkylating agents

The effect of spermine binding on the electrostatic potential of DNA is evaluated. The calculations are performed for the essential reactive sites, atoms N7 and O6 of guanine, N3 and N7 of adenine, of the nucleic acid and for its surface envelope. An important weakening of the potential is found affecting all the important reactive sites in both grooves and spreading moreover along the polynucleotide chain far away from the site of binding of the ligand. These results are discussed in connection with the experimentally observed inhibitory effect of spermine binding on DNA methylation by carcinogenic agents.     

Seed cryopreservation and micropropagation of the federally threatened species,Price’s potato-bean (Apios priceana B.L. Robins.)

Apios priceana, commonly known as Price’s potato-bean, is a perennial species native to the Southeastern US. Habitat destruction has caused A. priceana to become rare, and it is federally listed as threatened. Protocols developed for in vitro germination, shoot micropropagation, in vitro rooting, shoot establishment in soil, and seed cryopreservation will assist in the safeguarding and conservation of dwindling natural populations. Seeds were germinated in vitro on plant growth regulator (PGR)-free Murashige and Skoog (MS) medium after seed sterilization in H₂O₂ and seed nicking. Greatest shoot multiplication occurred on MS medium with BAP/IBA/GA₃ at 2.22/0.49/1.44 μM with 2.0 g/l Phytagel and pH adjusted to 5.7. Shoots rooted in vitro in MS medium with 3.2 μM IBA. Shoots rooted in vitro rapidly established in greenhouse potting mix, usually showing new growth within 2 wk, with tuber formation by the end of the growing season. Plants transferred to a forest setting in late winter survived, grew throughout the summer, and became dormant in the fall. In small post cryopreservation tests with A. americana and A. priceana seeds, air or desiccant-dried to water contents below 10% but above 2.5%, germination reached 87–90%.