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Changes in iron(II) and iron(III) content in a solution of humic acids during coagulation by means of monomeric iron(III) salts

100%

Libecki B. , Dziejowski J.

Polish Journal of Environmental Studies

2010

tom 19

nr 5

This study discusses the results of laboratory analyses investigating the chemical coagulation of a model of humic acid solution with the use of monomeric iron(III) salts – chloride and sulfate – in a standard coagulation test environment. The objective of the study was to determine changes in iron compound concentrations in the tested solution as a result of coagulation. The following parameters were analyzed in solution samples: changes in COD, colour, turbidity, suspended solids, pH, and streaming potential in relation to the applied coagulant dose. The content of total iron (Fetotal) and iron(II) was determined in solution samples after coagulation. The lowest Fetotal concentrations were observed following the use of optimal coagulant doses, and higher doses led to a repeated increase in total iron levels. In purified solution samples, iron(III) was partially reduced to iron(II) with an 8-42% share of Fetotal, depending on salt type and the applied dose.

Calcium-binding calmyrin forms stable covalent dimers in vitro, but in vivo is found in monomeric form

84%

Sobczak A. , Blazejczyk M. , Piszczek G. , Zhao G. , Kuznicki J. , Wojda U.

2005

tom 52

nr 2

The EF-hand Ca2+-binding protein calmyrin is expressed in many tissues and can interact with multiple effector proteins, probably as a sensor transferring Ca2+ signals. As oligomerization may represent one of Ca2+-signal transduction mechanisms, we characterised recombinant calmyrin forms using non-reducing SDS/PAGE, analytical ultracentrifugation and gel filtration. We also aimed at identification of biologically active calmyrin forms. Non-reducing SDS/PAGE showed that in vitro apo- and Ca2+-bound calmyrin oligomerizes forming stable intermolecular disulfide bridges. Ultracentrifugation indicated that at a 220 μM initial protein concentration apo-calmyrin existed in an equilibrium of a 21.9 kDa monomer and a 43.8 kDa dimer (trimeric or tetrameric species were not detected). The dimerization constant was calculated as Ka = 1.78 × 103 M–1 at 6oC. Gel filtration of apo- and Ca2+-bound calmyrin at a 100 μM protein concentration confirmed an equilibrium of a monomer and a covalent dimer state. Importantly, both monomer and dimer underwent significant conformational changes in response to binding of Ca2+. However, when calmyrin forms were analyzed under non-reducing conditions in cell extracts by Western blotting, only monomeric calmyrin was detected in human platelets and lymphocytes, and in rat brain. Moreover, in contrast to recombinant calmyrin, crosslinking did not preserve any dimeric species of calmyrin regardless of Ca2+ concentrations. In summary, our data indicate that although calmyrin forms stable covalent dimers in vitro, it most probably functions as a monomer in vivo.