Allison Cockrell - Low-Molecular-Mass Metal Complexes in the Mouse Brain

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      Sean P. McCormick, Mrinmoy   Chakrabarti, Allison L. Cockrell, Jinkyu Park,   Louise C. Abbott, Lora S. Lindahl, and Paul A. Lindahl (2013)   Metallomics 5 (3), 232 – 241


        The presence of labile low-molecular-mass (LMM, defined as <10   kDa) metal complexes in cells and super-cellular structures such   as the brain has been inferred from chelation studies, but direct   evidence is lacking. To evaluate the presence of LMM metal   complexes in the brain, supernatant fractions of fresh mouse   brain homogenates were passed through a 10 kDa cutoff membrane   and subjected to size-exclusion liquid chromatography under   anaerobic refrigerated conditions. Fractions were monitored for   Mn, Fe, Co, Cu, Zn, Mo, S and P using an on-line ICP-MS. At least   30 different LMM metal complexes were detected along with   numerous P- and S- containing species. Reproducibility was   assessed by performing the experiment 13 times, using different   buffers, and by examining whether complexes changed with time.   Eleven Co, 2 Cu, 5 Mn, 4 Mo, 3 Fe and 2 Zn complexes with   molecular masses <4 kDa were detected. One LMM Mo complex   comigrated with the molybdopterin cofactor. Most Cu and Zn   complexes appeared to be protein-bound with masses ranging from   4-20 kDa. Co was the only metal for which the "free" or aqueous   complex was reproducibly observed. Aqueous Co may be sufficiently   stable in this environment due to its relatively slow   water-exchange kinetics. Attempts were made to assign some of   these complexes, but further efforts will be required to identify   them unambiguously and to determine their functions. This is   among the first studies to detect low-molecular-mass transition   metal complexes in the mouse brain using LC-ICP-MS.

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