Mercury (Hg) is toxic to living organisms and can be transformed among several forms or species in the environment. The most toxic form of Hg is methylmercury: this form of Hg is generated by the activity of HgcAB (an enzyme) in the cytoplasmic space of certain anaerobic microorganisms. All forms of Hg have a high affinity for sulfides and organic thiolates, which are ubiquitous in the environment. The mechanism by which various mercury species enter and exit cells is not known. Here, we used biomimetic model membranes to determine the passive transport of Hg species across membrane bilayers. We focused on the most environmentally relevant Hg species to assess their potential to enter the cell. One method for studying such transport processes into cells uses large unilamellar vesicles (LUVs). These vesicles consist of a single phospholipid bilayer, and separates the enclosed fluid from the bulk solution, much like a cellular membrane. Phospholipid vesicles can be prepared from pure phospholipids, and we tested two of these. We evaluated three methods to separate the Hg-loaded vesicles from dissolved Hg, which is necessary for quantifying Hg species associated with LUVs. The methods were: (1) size exclusion chromatography, (2) high-speed centrifugation, and (3) ultrafiltration. Size exclusion chromatography and centrifugation resulted in incomplete separation and low phospholipid vesicle yields, but ultrafiltration resulted in a clean separation. Thus, ultrafiltration can be used to quantify the transport of Hg species across phospholipid bilayers. Now that we have an idea about the mechanism of mercury transport, we can continue to study how mercury enters the cell to be methylated. Future work looks to kinetic studies to understand and determine the rate of transport, to potentially discover methods to combat mercury methylation.<br/>

Methods to study the interactions of mercury species with biological membranes

2019 Spring National Meeting

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