Structure of the Glycyl-L-histidyl-L-lysine--copper(II) complex in solution

Optical, electron paramagnetic resonance, and electron spin-echo envelope spectroscopies were used to examine the structure of the Cu(II) complex of glycyl-L-histidyl-L-lysine (GHL) in solution. At neutral pH, GHL forms a mononuclear 1:1 Cu(II) compound having an EPR spectrum resembling that of Cu(II) equatorially coordinated by two or three nitrogen atoms. Electron spin-echo studies demonstrate that one of these is located in the histidyl imidazole ring. A pH titration of Cu(II)-GHL shows three optical transitions with apparent pKs of 3.6, 9.2 and 11.4 and molecularities, with respect to protons, of 2, 2, and 1, respectively. At the lowest pK, GHL binds Cu(II), forming the species present at physiological pH. At elevated pH, spectroscopic experiments suggest that an alteration of the Cu(II) structure occurs, yet the bound imidazole is retained. These solution studies are consistent with nitrogen coordination of Cu(II) in Cu(II)-GHL, but the solid-state polymeric structure, with oxygen-bridged Cu(II) pairs as previously determined by X-ray crystallographic analysis [Pickart, L., Freedman, J. H., Loker, W. J., Peisach, J., Perkins, C. M., Steinkamp, R. E., & Weinstein, B. (1980) Nature (London) 288, 715-717; C. M. Perkins, N. J. Rose, R. E. Steinkamp, L. H. Jensen, B. Weinstein, and L. Pickart, unpublished results], does not exist in solution.     

Studies of the coordination of rare earth and transition metal nucleotide complexes by an electron spin echo method

Titrations of the paramagnetic rate earth ions Ce(III), Nd(III), Er(III), and Yb(III) with ATP, ADP, adenosine, and the hexametaphosphate ligands have been performed in order to establish the conditions required to form saturated complexes. These titrations have been made by recording the decay envelope of electron spin echoes for a range of different concentrations of the species concerned and observing the ‘nuclear modulation effect’ in the echo envelope. This novel method can be used when optical titrations are not feasible. It also yields additional information concerning changes in the number and nature of the coordinating groups, in the distances of these groups from the paramagnetic ion, and in the degree of water coordination in the primary sphere. It was shown that: (a) ATP has a greater affinity than ADP for rate earth ions; (b) Ce(III) has a greater affinity than Nd(III) for ATP; (c) the interaction between rate earth ions and ³¹P nuclei in the added phosphates is greatest for cations with the smallest radii; (d) more phosphate groups are bound in hexametaphosphate complexes of rate earth ions than in the corresponding ATP complexes; (e) some of the coordination sites in rare earth ATP complexes are occupied by water. In othe studies performed with paramagnetic transition metal ions, it was shown that Co(II) can, under certain conditions, bind to the adenine moiety of ATP.     

Effect of particle size and temperature on the conformation and physiological behavior of apolipoprotein E bound to model lipoprotein particles

The effect of particle size and structural order/disorder of the lipid domain on the conformation and physiological behavior of lipid-associated apolipoprotein E (apoE) was evaluated. Circular dichroic (CD) spectra of apoE bound to large (LME) and small (SME) microemulsion particles, composed of dimyristoylphosphatidylcholine (DMPC) and cholesteryl oleate (CO), and to DMPC disks revealed that at 4 degrees C, where all of the lipid constituents were in an ordered state, apoE bound to LME displayed approximately 60% alpha-helicity, while apoE bound to SME and DMPC disks displayed 73% and 95% helicity, respectively. Over the temperature range 4-50 degrees C, encompassing the lipid thermal transitions, only apoE bound to LME demonstrated an abrupt change in its CD spectrum (decrease in alpha-helicity) in response to temperature. To determine the source of the abrupt CD change, the constants for dissociation (Kd) of apoE from the surface of the large and small microemulsion particles were determined at 4, 25, and 37 degrees C. These results demonstrated that at 4 degrees C, the KdS for binding of apoE to the LME and SME were approximately equal; however, between 4 and 25 degrees C, there was a 5-fold increase in the Kd for binding of apoE to the LME, whereas the Kd for binding to the SME remained constant. The physiological effects of these differences in apoE secondary structure and equilibrium binding were examined by measuring the capacity of each apoE-containing particle to complete with LDL for binding to human fibroblasts, and by measuring the capacity of the apoE-microemulsion particles to suppress HMG-CoA reductase activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Educating Hearts and Minds: Reflections on Japanese Preschool and Elementary Education

Educating Hearts and Minds: Reflections on Japanese Preschool and Elementary Education. Catherine C. Lewis. New York: Cambridge University Press, 1995. 249 pp.