Polymer conformation: 2. Rapid methods for locating contact-free molecular structures with particular reference to sidegroup interactions,linkage maps and crystal packing of rigid helical chains

Paper 1 in this series¹ outlined a method for identifying sets of backbone conformations of a polymer which are of a given helical type. This paper is concerned with fast methods for the calculation and mapping of contact-free structures in cases where the structure consists of two rigid molecular groups and where the position of each group varies by rotation about its own distinct axis. In particular, it is shown how such methods can be used to locate the neighbourhoods of crystal packing minima for a helical polymer chain, which could be generated by the method of Paper 1 and which is to be packed rigidly into a lattice. The method does not possess the flexibility of a full refinement procedure, but its advantages, apart from its conjectured speed, include an exactly known level of exhaustion of the examined variables and immunity to false packing minima and choice of initial starting position. Together, the methods may provide a means for checking the capability of refinement procedures to locate packing minima.     

Intracellular location of nitrate reductase and nitrite reductase in spinach and sunflower leaves

Summary Chloroplasts have been isolated from spinach and from sunflower which retain their outer membrane and their stroma protein as determined both by ability to fix CO₂ and evolve O₂ at high rates, and by appearance under the phase contrast microscope. Such chloroplasts contain both nitrate and nitrite reductase activity. However, calculations on the distribution of these enzymes, when compared with the distribution of pyruvate kinase and cytochrome c oxidase activity, demonstrate that the larger part of both nitrate and nitrite reductase is located outside of the chloroplast.Supported in part by the National Research Council of Canada.     

Stimulation of cell growth and proliferation in NIH-3T3 cells by onion and garlic oils

Onion and garlic oil were seen to shorten the cell-doubling time and stimulate the growth and proliferation of NIHY-3T3 cells. FNollowing treatment with either onion or garlic oil, an increase in the growth rate and almost a 2-fold increase in cell number over the control was observed within a 24-hour period. Phorbol myristate acetate when given simultaneously with either oil appeared to nullify both effects. FNollowing exposure to low doses (< 10 µm/ml) of either oil, an increase in cell survival, not seen with the oil control tricaprylin, was observed following a 5-day exposure period. At higher concentrations cell survival decreased proportionately in all cases. The appearance of multinucleated cells, which increased with dose and time, was also observed following treatment with both garlic and onion oil.Abbreviations EMEMM Eagles Minimal Essential Medium - MCN mean cell number - PMA phorbol myristateacetate - RCE relative cloning efficiency - SEM standard error of the mean