Validation of TPEN as a Zinc Chelator in Fluorescence Probing of Calcium in Cells with the Indicator Fura-2

Fura-2 is widely used as a fluorescent probe to monitor dynamic changes in cytosolic free calcium in cells, where Ca²⁺ can enter through several types of voltage-operated or ligand-gated channels. However, Fura-2 is also sensitive to other metal ions, such as zinc, which may be involved in ionic channels and receptors. There is interest, in particular, in studying the synapses between mossy fibers and CA3 pyramidal cells which contain both calcium and high quantities of free or loosely bound zinc. We have found, through fluorescence probing, that endogenous zinc inhibits mossy fiber calcium transients. However, since these results might be explained by an effect of the zinc chelator N,N,N’,N’-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) on the spectral properties of Fura-2, we have carried out a validation of the method through fluorescence excitation spectra of the complex Fura-2/calcium, and show that TPEN does not affect these spectra. This supports the idea that the observed calcium enhancement is related to a zinc inhibition of presynaptic calcium mechanisms, and confirms the use of the chelator TPEN as a general procedure for the biophysical study of Ca(II) in the presence of Zn(II) using Fura-2.     

Specific and nonspecific collapse in protein folding funnels

Experiments with fast folding proteins are beginning to address the relationship between collapse and folding. We investigate how different scenarios for folding can arise depending on whether the folding and collapse transitions are concurrent or whether a nonspecific collapse precedes folding. Many earlier studies have focused on the limit in which collapse is fast compared to the folding time; in this work we focus on the opposite limit where, at the folding temperature, collapse and folding occur simultaneously. Real proteins exist in both of these limits. The folding mechanism varies substantially in these two regimes. In the regime of concurrent folding and collapse, nonspecific collapse now occurs at a temperature below the folding temperature (but slightly above the glass transition temperature).     

Liquid 2-oxazolidones. I. Dielectric constants,viscosities, and other physical properties of several liquid 2-oxazolidones

Eight derivatives of 2-oxazolidone,, have been synthesized by the Homeyer method and purified by fractional freezing or fractional distillation to obtain low-conducting liquids. Dielectric constants, viscosities, densities, and refractive indices of these 2-oxazolidones have been determined at several temperatures within the range 25 to 75°C. Values for activation energies of viscous flow also have been calculated. The isomeric 3-methyl and 5-methyl derivatives of 2-oxazolidone have high dielectric constants which differ only slightly from that of water. The 3-substituted (or N-substituted) 2-oxazolidones exhibit the most favorable combination of physical properties, stability, and ease of purification and appear to have excellent potential as new nonaqueous solvents.Based on a portion of the Ph. D. dissertation of H. L. Huffman, Jr., University of Kentucky, 1972. Presented in major part at the 21 st Southeastern Regional Meeting of the American Chemical Society, Richmond, Virginia, 1969.     

Characterization of an immobilized antibody-enzyme complex

Antiserum specific for propanediol dehydrogenase, an enzyme found inNeisseria gonorrhoeae cells, has been immobilized to glass. When mixed withN gonorrhoeae cell lysates, the immobilized antibody (IMA) binds the enzyme. Over 70% of the calculated adsorbed activity can be recovered from the immobilized antibody-enzyme (IMA-E) complex. When mixed with bacterial lysates prepared from different organisms having propanediol dehydrogenase-like activity, the IMA specifically adsorbed the enzyme from theN gonorrhoeae lysate. IMA-E complexes have been prepared and their kinetic, temperature and chemical stability, and antigenic properties investigated. These studies demonstrated the feasibility of using an immobilized antibody in the detection of the propanediol dehydrogenase enzyme.     

Pioneering O.R.

This paper describes the critical start-up period of a new Operational Research unit in industry. Four principles for success evolved and are discussed against a background of practical work.     

Uniqueness of the inversive plane of order 7

A search has shown that any inversive plane of order 7 must be isomorphic with the Miquelian plane. The method used was explicitly set out in a companion paper, which was concerned with a plane of order 5.     

Greedy sums of distinct squares

When a positive integer is expressed as a sum of squares, with each successive summand as large as possible, the summands decrease rapidly in size until the very end, where one may find two 's, or several 's. We find that the set of integers for which the summands are distinct does not have a natural density but that the counting function oscillates in a predictable way.

     

MODELS OF HOST-PARASITOID INTERACTIONS TO DETERMINE THE OPTIMAL INSTAR OF PARASITIZATION FOR PEST CONTROL

Four models are presented to investigate the effects of the host instar that is parasitized on host equilibrium numbers. The models are age structured and density dependent. The models indicate that the equilibrium density of adult hosts is a positive function of the host age at attack. This result is independent of the host survivorship curve. The effects of the other parameters are outlined, and compared for the various positions of density dependence. The equilibria of both parasitoids and hosts are generally larger when density dependence is in the parasitoids than when in the hosts. Numerical runs indicate that the birth rate and stage-specific survivorship of the hosts are the most important parameters of the system in determining both stability around equilibrium and the host growth rate below equilibrium.