Coordinative Binding of Divalent Cations with Ligands Related to Bacterial Spores

Abstract

It has been repeatedly postulated that the high heat resistance of bacterial spores is due to stabilization of biopolymers in the spore interior by a solid deposit of protective cement consisting of coordination complexes of ligands with divalent metal ions. This report presents data on metal-binding characteristics of some of the ligands related to spores as determined by means of potentiometric equilibrium measurements under conditions of temperature and ionic strength (t = 25.0 degrees C; mu = 1.0 KNO(3)) identical with those reported earlier by the authors in order to facilitate correlation by using comparable data. The spore ligands investigated in this study included 2,6-pyridinedicarboxylic acid (DPA), alpha,epsilon-diaminopimelic acid, D-glutamic acid, and D-alanine in a ratio of 1:1 with metal ions which are known to play a role in heat resistance of spores. Stability constants of the chelates of these spore ligands with metal ions such as Ca(II), Mg(II), Cu(II), Ni(II), Zn(II), Co(II), and Mn(II) have been determined. In general the metal chelates of DPA exhibited the greatest stability. On the basis of a consideration of the stability data together with the known configurations of the ligand and the coordination requirements of the metal ions, possible structures indicating the coordinate binding of the spore ligands with the metal ions are presented. All the metal chelates except those of Ca(II) were found to undergo hydrolysis and separation of solid phase in the pH range 7-8.5. The relatively greater hydrolytic stability of Ca(II) chelates and the high affinity of DPA for metal ions appear to be of biological significance insofar as these two spore components are more widely associated with the heat resistance of bacterial spores.

Detection of Bacterial Spores with Lanthanide−Macrocycle Binary Complexes

“…This was expected, as CaDPA is a stable neutral salt (log K CaDPA = 4.0542), and the mode by which most bacterial spores store the high concentration of dipicolinic acid present in the spore cortex 14. The data were fit to a two-state chemical equilibrium model similar to that used in the BAC assay, and competition constants were calculated for Ca 2+ competing with the Tb(DO2A) + binary complex (log K cation = -4.36 ± 0.23) and the Tb 3+ ion alone (log K cation = -3.68 ± 0.17) for DPA 2- .…”

Effects of Mn and Fe Levels on Bacillus subtilis Spore Resistance and Effects of Mn 2+ , Other Divalent Cations, Orthophosphate, and Dipicolinic Acid on Protein Resistance to Ionizing Radiation

“…Such Mn complexes are extremely radioprotective of irradiated DNA-modifying enzymes and metabolic enzymes, preventing protein carbonylation and preserving their activity (18). DPA falls within this structural rubric and is a good Mn chelator (11), and it was therefore tested for its ability to protect an enzyme from ionizing radiation when combined with phosphate buffer, Mn 2ϩ , Ca 2ϩ , and Mg 2ϩ . Using the activity of the restriction endonuclease BamHI as a reporter of protein function, we tested the radioprotective properties of mixtures of DPA, cations, and P i at concentrations for most of these species that are well below those in spores-Mn 2ϩ at 0.01 to 1 mM, DPA at 5 to 10 mM, and P i at 20 mM-although these values for P i and divalent cations are in the ranges for many cell types, including eukaryotes (40).…”

Crystallochemical formula as a tool for describing metal–ligand complexes – a pyridine-2,6-dicarboxylate example

“…Pyridinedicarboxylates are of great interest owing to their practical importance, e.g. their biological activity (Chung et al, 1971;Lindsay & Murrell, 1986;Hwang et al, 2003), and diverse coordination abilities (Lindsay & Murrell, 1986;Koman et al, 2000;Yue et al, 2005). They can be used to obtain various metal-organic frameworks (Robin & Fromm, 2006), which in some cases exhibit such properties as interesting optical behavior (LeCours et al, 1996;Darling et al, 2000) and magnetism (Brandon, Rittenberg et al, 1998;Brandon, Rogers et al, 1998).…”