Impact of Zn2+ introduced into the central cavity of meso-tetra(4-pyridyl)porphine on its spectroscopic features

2021 ◽  
Vol 113 ◽  
pp. 110893
Author(s):  
M.M. Makhlouf ◽  
M.M. Shehata
Keyword(s):  
Author(s):  
William H. Massover

Each molecule of ferritin (d = 130Å) contains a core of iron surrounded by a 24-subunit protein shell. The amount of iron stored is variable and is present within the central cavity (d = 80Å) as a hydrated ferric oxide equivalent to the mineral, ferrihydrite. Many early ultrastructural studies of ferritin detected regular patterns of a multiparticulate substructure in the iron-rich core [e.g., 3,4], Each small particle was termed a “micelle“; a theory became widely accepted that a core consisted of up to six micelles positioned at the vertices of an octahedron. Other workers recognized that the apparent micelles were smaller or even disappeared if images were recorded closer to exact focus [e.g., 5]. In 1969, Haydon clearly established that the observed substructure was really an imaging artifact; each apparent micelle was only a dot in the underfocused phase contrast image of the supporting film superimposed on the amplitude image of the strongly scattering metal.


Author(s):  
William H. Massover

Molecules of the metalloprotein, ferritin, have an outer shell comprised of a polymeric assembly of 24 polypeptide subunits (apoferritin). This protein shell encloses a hydrated space, the central cavity, within which up to several thousand iron atoms can be deposited as the biomineral, ferrihydrite. The actual pathway taken by iron moving across the protein shell is not known; an analogous question exists for the demonstrated entrance of negative stains into the central cavity. Intersubunit interstices at the 4-fold and 3-fold symmetry axes have been defined with x-ray diffraction, and were hypothesized to provide a pathway for penetration through the outer shell; however, since these channels are only 4Å in width, they are much too small to allow simple permeation of either hydrated iron or stain ions. A different hypothesis, based on studies of subunit dissociation from highly diluted ferritin, proposes that transient gaps in the protein shell are created by a rapid reversible subunit release and permit the direct passage of large ions into the central cavity.


Author(s):  
James F. Hainfeld ◽  
Frederic R. Furuya ◽  
Kyra Carbone ◽  
Martha Simon ◽  
Beth Lin ◽  
...  

A recently developed 1.4 nm gold cluster has been found to be useful in labeling macromolecular sites to 1-3 nm resolution. The gold compound is organically derivatized to contain a monofunctional arm for covalent linking to biomolecules. This may be used to mark a specific site on a structure, or to first label a component and then reassemble a multicomponent macromolecular complex. Two examples are given here: the chaperonin groEL and ribosomes.Chaperonins are essential oligomeric complexes that mediate nascent polypeptide chain folding to produce active proteins. The E. coli chaperonin, groEL, has two stacked rings with a central hole ∽6 nm in diameter. The protein dihydrofolate reductase (DHFR) is a small protein that has been used in chain folding experiments, and serves as a model substrate for groEL. By labeling the DHFR with gold, its position with respect to the groEL complex can be followed. In particular, it was sought to determine if DHFR refolds on the external surface of the groEL complex, or whether it interacts in the central cavity.


Author(s):  
S. Kanasiya ◽  
S. K. Karmore ◽  
S. K. Deshmukh ◽  
R. K. Barhaiya ◽  
S. K. Gupta

The present study was conducted on ten each uropygial glands of 6 to 8 months old healthy Kadaknath and White Leghorn breeds of poultry. The tissue samples were stained by H and E for normal histological structures, Verhoeff’s stain for collagen and elastic fibers, PAS (Periodic Acid Schiff’s) for glycogen and Alcian Blue PAS method for acid mucopolysaccharides. The uropygial gland in Kadaknath and White Leghorn was composed of two lobes. Each lobe had a single duct and these ducts were joined together by isthmus. The thickness of capsule was more in White Leghorn than Kadaknath breed. The lumen of tubules showed higher concentration of secretary product in Kadaknath breed. Numbers of tubules were higher in Kadaknath. No aggregation of lymphocytes was found in the preen gland of White Leghorn, whereas in Kadaknath, there was large number of lymphocytes aggregation alongwith lymphatic nodules. Melanin pigmentation was the characteristic feature of Kadaknath which was found towards the central cavity and in between ductules. The capsule of White Leghorn showed intense PAS activity, while moderate activity was found in Kadaknath breed of poultry. Intense ACPase reaction was noticed in capsule of uropygial gland of Kadaknath and White Leghorn breeds of poultry.


2021 ◽  
Vol 22 (7) ◽  
pp. 3572
Author(s):  
Jeff Abramson ◽  
Ernest M. Wright

Active transport of sugars into bacteria occurs through symporters driven by ion gradients. LacY is the most well-studied proton sugar symporter, whereas vSGLT is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. LacY has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. vSGLT has a core structure of 10 TM helices organized in two inverted repeats (TM 1–5 and TM 6–10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in LacY the proton (H3O+) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.


2012 ◽  
Vol 29 ◽  
pp. 123-136 ◽  
Author(s):  
Qiang Yu ◽  
Zhifeng Wang ◽  
Ershu Xu ◽  
Hongli Zhang ◽  
Zhenwu Lu ◽  
...  

2020 ◽  
Vol 76 (8) ◽  
pp. 1213-1221
Author(s):  
Elizabeth C. Manickas ◽  
Matthias Zeller ◽  
Curtis M. Zaleski

The syntheses and crystal structures for the compounds tetra-μ-aqua-tetrakis{2-[azanidylene(oxido)methyl]phenolato}tetrakis(μ2-3-hydroxybenzoato)dysprosium(III)tetramanganese(III)sodium(I) N,N-dimethylacetamide decasolvate, [DyMn4Na(C7H5O3)4(C7H4NO2)4(H2O)4]·10C4H9NO or [DyIIINa(4-OHben)4{12-MCMn(III)N(shi)-4}(H2O)4]·10DMA, 1, and tetra-μ-aqua-tetrakis{2-[azanidylene(oxido)methyl]phenolato}tetrakis(μ2-3-hydroxybenzoato)dysprosium(III)tetramanganese(III)sodium(I) N,N-dimethylformamide tetrasolvate, [DyMn4Na(C7H5O3)4(C7H4NO2)4(H2O)4]·4C3H7NO or [DyIIINa(3-OHben)4{12-MCMn(III)N(shi)-4}(H2O)4]·4DMF, 2, and where MC is metallacrown, shi3− is salicylhydroximate, 3-OHben is 3-hydroxybenzoate, DMA is N,N-dimethylacetamide, 4-OHben is 4-hydroxybenzoate, and DMF is N,N-dimethylformamide, are reported. For both 1 and 2, the macrocyclic metallacrown consists of an [MnIII—N—O] ring repeat unit, and the domed metallacrown captures two ions in the central cavity: a DyIII ion on the convex side of the metallacrown and an Na+ ion the concave side. The MnIII ions are six-coordinate with an elongated tetragonally distorted octahedral geometry. Both the DyIII and Na+ ions are eight-coordinate. The DyIII ions possess a square-antiprismatic geometry, while the Na+ ions have a distorted biaugmented trigonal–prismatic geometry. Four 3-hydroxybenzoate or 4-hydroxybenzoate ligands bridge each MnIII ion to the central DyIII ion. For 1, whole-molecule disorder is observed for the main molecule, excluding only the DyIII and Na+ ions, and the occupancy ratio refined to 0.8018 (14):0.1982 (14). Three DMA molecules were refined as disordered with two in general positions by an approximate 180° rotation and the third disordered twice by general disorder as well as by an exact 180° rotation about a twofold axis that bisects it. The occupancy ratios refined to 0.496 (8):0.504 (8), 0.608 (9):0.392 (9), and 2×0.275 (7):2×0.225 (7), respectively. For 2, segments of the metallacrown are disordered including the DyIII ion, one of the Mn ions, two of the Mn-bound 4-hydroxybenzoate ligands, the Mn-bridging salicylhydroximate ligand, and portions of the remaining three shi3− ligands. The occupancy ratio for the metallacrown disorder refined to 0.849 (9):0.151 (9). Two DMF solvent molecules are also disordered, each over two orientations. The disorder ratios refined to 0.64 (3):0.36 (3) and to 0.51 (2):0.49 (2), respectively. For 2, the crystal under investigation was refined as a non-merohedric twin by a 90° rotation around the real a axis [twin ratio 0.9182 (8):0.0818 (8)].


2017 ◽  
Vol 53 (2) ◽  
pp. 408-411 ◽  
Author(s):  
Jerico R. Piper ◽  
Lewis Cletheroe ◽  
Christopher G. P. Taylor ◽  
Alexander J. Metherell ◽  
Julia A. Weinstein ◽  
...  

The array of naphthyl chromophores in a self-assembled cage can effect photoinduced energy- or electron-transfer to guests in the central cavity.


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