Re: cell transport protein, magnesium

Hi,

As you point out, magnesium ion (Mg²⁺) transport can occur via the ATPase pathway. Mg²⁺ could most likely be transported via pathways such as the amino acid transporter as well, provided the Mg²⁺ ion does not interfere with transport. But the more likely mechanism for Mg²⁺ transport is through Mg²⁺ transporters, many of which have only recently been characterized on a molecular level. (For reviews of Mg²⁺ transporters, see "Molecular identification of ancient and modern mammalian magnesium transporters" by G. Quamme, Am J Physiol Cell Physiol. 2010 Mar;298(3):C407-29 and "Insight into renal Mg2+ transporters" by S. Ferrè, et al., Curr Opin Nephrol Hypertens. 2011 Mar;20(2):169-76). In addition, claudins are cell membrane proteins that are key components of tight junctions, and some of these are involved in Mg2+ transport between cells (paracellular transport) in the intestinal epithelium (Kausalya P.J., et al., 2006).

There is 0.5 mM Mg²⁺ outside of the cell, and 2 mM free Mg²⁺ inside of the cell, though if you were to include the Mg²⁺ bound to proteins and nucleic acids, the intracellular Mg²⁺ concentration would be approximately 20 mM (Molecular Biology of the Cell, Alberts et al. 2002). Mg²⁺ is a smaller ion than Ca²⁺, but it is more electronegative and has a more substantial hydration sphere, which adds to its size. These chemical properties would explain why some Mg²⁺ transporters are structurally different from other ion transporters/channels.

As Mg²⁺ is so important for biological processes, more information about Mg²⁺ transport will undoubtedly be discovered in the future. I hope this helps to answer your question!

Sarah Earley, PhD
Massachusetts General Hospital

References:
Quamme G (2010) Molecular identification of ancient and modern mammalian magnesium transporters. Am J Physiol Cell Physiol. 298(3):C407-29 .

Ferrè S, Hoenderop JG, Bindels RJ (2011) Insight into renal Mg2+ transporters. Curr Opin Nephrol Hypertens. 20(2):169-76.

Kausalya PJ, Amasheh S, Günzel D, Wurps H, Müller D, Fromm M, Hunziker W (2006) Disease-associated mutations affect intracellular traffic and paracellular Mg2+ transport function of Claudin-16. J Clin Invest. 116(4):878-91.

Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002.