Science Buddies: "Ask an Expert"

In the California delta there is a lot of methylmercury, being so much of it in the water allows the fish of the region to ingest it. When a fish ingests methylmecury it binds to the muscle using amino acids, which enables the fish inedible. My experiment is to caught a delta bass and fillet it (I have my fishing license and it will be legal limit). The methylmercury attached to the muscle with not come off by simply cleaning the fish. So I researched enzymes that broke down amino acids and I found that protease does exactly that. So I will be making a protease solution and bathing the fillet in it. After bathing the fillet I will test the solution for mercury. And if my hypothesis is correct, the amino acid bonds will break and the methylmercury will just be left on top which will fall in the solution and test positive for mercury. If this is successful the seafood of the delta will become available for human consumption. If anyone has a better experimental procedure or any insight it would be much appreciated! Thank you for your time!

Hi There
My complements on coming up with interesting and creative questions and ideas. In addition to this question, your question about sharks and cancer was also quite interesting. I think you are right that risk management for seafood in the Delta and other areas is worth looking into. Proteases have been successfully employed to separate Hg from amino acids in the lab. Here are some things to think about:
1. This method has been done to measure mercury in fish tissue: http://pubs.rsc.org/en/content/articlep ... age=search (I found this by searching "protease methylmercury" in google)
2. Once the methylmercury -amino acid bonds are broken, there is still the need to separate out the methylmercury so that it is not consumed. In some circumstances, methylmercury is volatile, so maybe there is a way to get it to vaporize into the air?
3. The resulting product is likely to be a "fish goop" or "fish broth" or "fish paste" of some sort. So another question will be how to make it something that will be enjoyable to eat. Certainly, fish sauce and other liquid fish products have a role in many culinary dishes, and one of the questions might be recipes that would be tasty.
4. The protease used must be, itself, safe to eat. In an internet search I found that proteases are found in pineapple and unripe papayas and other fruit so maybe these could be kinds to try: http://www.livestrong.com/article/26284 ... e-enzymes/
5. Testing for mercury is a challenge. Maybe there is some local laboratory that would be willing to work with you on laboratory testing for mercury.

The current procedures for reducing methylmercury contamination in fish focus on people thinking about which fish species or types have more or less mercury in their tissue, how mercury varies spatially by region, and how much fish is relatively safe to eat. For California there is actually a database and a lot of literature on fish contamination that can be used to look at spatial patterns in this. Google search "swamp fish contamination" to see some of this.

Hope there are some useful ideas here for you, and do keep us posted as you further develop your project!

Hi Royce,

Mercury contamination of fish and shellfish is a big worry for people who like seafood, and having a way to remove it would be great. However, there are some problems with your proposed method. Firstly, proteases are enzymes that break proteins into smaller pieces called peptides by cleaving specific amino acid bonds. For example, a common protease is trypsin which is found in our digestive system [http://en.wikipedia.org/wiki/Trypsin]. It breaks down proteins by cleaving them at either lysine or arginine—but nowhere else. Pepsin is a protease in the stomach and it cleaves proteins specifically at aromatic amino acids such as phenylalanine, tryptophan and tyrosine [http://en.wikipedia.org/wiki/Pepsin].

Proteases break down proteins and if you do that to a fish filet it will likely turn into mush--like meat that has been exposed too long to too much meat tenderizer.

I did a search for methyl mercury (MeHg) binding to proteins and found several references. This one tested tuna and found Hg bound to a protein called skeletal muscle myosin--http://www.ncbi.nlm.nih.gov/pubmed/22699869
The MeHg was found attached to the amino acid cysteine by a stable bond with the sulfhydryl group. Proteases can be used to cleave the protein into smaller peptides but this would not remove the mercury from the fish filet.

You have a great goal but you need to discover something that would specifically cleave the bond holding the MeHg to the amino acid and then bind the MeHg to something that can be collected and disposed of safely. Even if the MeHg is separated from the amino acid it will still be in solution. There are chelators that might be used to bind the mercury but the fish would still have to be approved as edible.

I think the most interesting aspect of the mercury problem is how elemental Hg or Hg2+ ions (divalent mercury), which are toxic to humans but not readily absorbed, become the much more toxic MeHg. I found an interesting article about this [http://www.whoi.edu/oceanus/feature/how ... -into-fish] that says the process is probably biological but the organism that does the conversion is unknown. The author thinks it is probably a marine bacterium that lives in ocean sediments, but more research needs to be done.

Let us know if you have more questions. We’re here to help.

Sybee