No abstract

No abstract

BIOCHEMISTRY: COMMONER ET AL. organisms suggests that the system yielding acetate from pyruvate may be involved in the mechanism controlling the balance between prophage and host. We could find no effect by the addition of lipoic acid, or any other of the adjuvants, on systems of virulent phase infection-by T1-of either lysogenic or nonlysogenic organisms as measured by efficiency of infection, survivors, and burst size, in onestep growth experiments.6 This finding was not unexpected. In a system of an organism invaded by a virulent phage the host must cope not only with the invading DNA but with the toxic protein moiety as well. An induced lysogenic organism where there is no foreign protein involved could thus be expected to be more amenable to restoration during the early phase after induction. However, it may be relevant that Spizizen7 has shown that E. coli grown on lactate or L-serine accumulates pyruvate after infection by phage T2 or T7, indicating that some alteration of pyruvate metabolism may be a concomitance of infection by virulent phage as well.

No abstract

Paramagnetic resonance spectra of free radicals are discussed, with emphasis upon observed hyperfine patterns. A brief description of a paramagnetic resonance spectrometer is given, and examples of applications to problems of physical, chemical, and biological interest are presented.The polyatomic free radicals may be contrasted in their paramagnetic resonance properties to the ions of the iron and rare-earth groups of transition elements. The free radicals possess spectroscopic splitting factors which usually differ only in the third decimal place from the free electron value, 2.0023, whereas the much stronger spin-orbit coupling which characterizes the transition elements may lead to values from one to about six. Both paramagnetic types exhibit exchange coupling which may render magnetic dipolar interactions between neighbouring ions less effective,l but this phenomenon is generally more striking for the polyatomic radicals in that resonance widths of as little as a few oersteds (10 Mc/s) or less for crystalline samples are not uncommon. Even the narrower lines of undiluted samples of the transition elements often have widths measured in hundreds of oersteds.The likelihood of a relatively sharp line quite near g = 2.0023 for each polyatomic free radical does not promise to make its study either very interesting or very fruitful. However, the strong exchange interaction often existing between neighbouring free radicals in an undiluted crystal or in a concentrated liquid solution reflects the extension of the unpaired electron wave function widely enough over space to provide regions of appreciable overlap between neighbouring molecules. Although the exchange interaction obscures possible intcresting line structure in more condensed samples, the spatial extent of the wavc function assures at least some magnetic coupling between the electron spin and many of the nuclear spins which may bc present in the polyatomic structure. The result, for sufficiently dilute samples, is a richness of hyperfine structure which for many free radicals has thus far proved to be overwhelming. Not only is this hyperfinc structure of some intrinsic interest, but it also plays an important role in a number of applications of the technique.The free radicals studied by paramagnetic resonance techniques are often extremely stable, in that lifetimes of the unpaired electron spin state may be indefinitely long, or at least a few hours. Others may rcquire certain precautions, such as protection from contact with oxygen or maintenancc of a certain solution pH, to achieve adequately long life. There are, of coursc, short-lived free radicals, in which there is usually considcrable interest, but they are less accessible to study for two reasons growing out of their rapid decay : first, it evidently becomes more difficult to maintain in the apparatus a significant number of free radicals (the spectrometer at Washington University requires at least 10-11 mole of a material with line width 1 oersted in order for resonance to be barely detectable at ...